essay on global warming advantages and disadvantages

Is There Any Upside to Global Warming?

Even Best-Case Scenario, the Cons Outweigh Any Possible Pros

Understanding Your Forecast
Storms & Other Phenomena
M.A., Geography, California State University - Northridge
B.A., Geography, University of California - Davis

The United Nations has been studying climate change and working to combat its effects since the first Earth Summit in 1992. The UN Intergovernmental panel's fifth report, published in late 2014, reiterates that global warming —more precisely called climate change—is happening and will likely not abate for centuries. The report also states with 95% certainty that the activity of humans has been the primary cause of increasing temperatures over the previous few decades, up from 90% in a previous report. We've heard the dire warnings—even if we have yet to heed them—but could there possibly be any advantages to climate change, and if so, could these upsides possibly outweigh the downsides? The short answer is no. Here's why.

Advantages of Global Warming? It's a Bit of a Stretch

The so-called advantages of climate are out there—if you're really looking but do they compensate for the disruption and destruction wrought by the disadvantages? Again, the answer is no but for die-hard fans of the global warming trend, advantages might include the following suspect scenarios:

The Arctic, Antarctic, Siberia, and other frozen regions of the earth might experience more plant growth and milder climates.
The next ice age could possibly be prevented.
The Northwest Passage through the formerly icy Canadian Arctic Archipelago could arguably open up to transportation.
Fewer deaths or injuries would occur due to arctic conditions.
Longer growing seasons could mean increased agricultural production in some areas.
Previously untapped oil and gas reserves might become available.

Disadvantages: Ocean Warming, Extreme Weather

For every minutely possible advantage to climate change, there is a much more profound and compelling disadvantage. Why? Since the oceans and weather are highly interconnected and the water cycle has an impact on weather patterns (think air saturation, precipitation levels, and the like), what affects the ocean affects weather. For instance:

Changes in ocean circulation and the resulting warmer temperatures disrupt the world's normal weather patterns, bringing about more extreme weather and an increased frequency of severe and catastrophic storms , such as hurricanes and typhoons. The increase in severe storms leads to a more frequent occurrence of such things as "hundred-year floods," decimation of habitats and property, not to mention, loss of life—human and otherwise.
Higher sea levels lead to flooding of lowlands. Islands and coastlines are engulfed by water leading to death and disease due to flooding.
The acidification of warming oceans leads to a loss of coral reefs. Coral reefs protect shorelines from heavy waves, storms, and floods and while they only cover about 0.1% of the ocean floor, reefs provide a habitat for 25% of the ocean's species. Demolished reefs lead to increased erosion and coastal property damage and the extinction of species.
Warming ocean waters means increased melting of glaciers and ice sheets. Smaller ice sheets form each subsequent winter, which has a devastating impact on the habitat of cold-climate animals and the Earth's reserves of freshwater. (According to the United States Geography Survey [USGS], 69% of the Earth's ice is locked in ice and glaciers.)
Less sea ice, warmer water, and increased acidity are catastrophic for krill which forms the base of the ocean's food web and feeds whales, seals, fish, and penguins. The plight of polar bears due to the loss of Arctic ice is well documented, but at the other end of the globe, in 2017 as a result of local climate change, in a colony of 40,000 Antarctic Adélie penguins, only two chicks survived. In 2013, in the wake of a similar event, none survived. Emperor penguin colonies are also expected to decline due to loss of sea ice and rising temperatures.

Disadvantages: Land Desertification

As weather patterns are disrupted and droughts intensify in duration and frequency, agricultural sectors are particularly hard hit. Crops and grasslands can't thrive due to lack of water. With crops unavailable, cattle, sheep, and other livestock don't get fed and die. Marginal lands are no longer useful. Farmers who find themselves unable to work the land lose their livelihoods. In addition:

Deserts become drier, leading to increased desertification , resulting in border conflicts in already water-scarce areas.
Decreased agricultural production leads to food shortages.
Starvation, malnutrition, and increased deaths result from food and crop shortages.

Disadvantages: Health, Social, and Economic Impact

In addition to climate change affecting weather patterns and food production, which in turn have a negative impact on the future of human race as well as the planet, climate change can also put the hurt on people's pocketbooks, the economy of an area on a larger scale, and health in general:

Insect-borne diseases increase. For example, if insects don't die off in an area because it no longer reaches the cold temperatures it once did, diseases those insects may carry—such Lyme disease—can proliferate more easily.
People from poorer, drier, hotter, or low-lying countries may attempt to emigrate to wealthier or higher-elevation locales seeking better (or at least nondeadly) conditions, causing tension among the existing population.
As climates warm overall, people use more energy resources for cooling needs, which will lead to a rise in air pollution and deaths from increasingly hot weather conditions that cannot be mitigated.
Allergy and asthma rates go up due to pollution exacerbated by the earlier and longer blooming of plants.
Cultural or heritage sites are destroyed due to increased extremes and acid rain.

Disadvantages: Nature Out of Balance

The environment around us is affected by climate change in a multitude of ways. The component parts of any ecosystem normally must maintain a delicate balance but climate change is throwing nature is out of whack—in some places more than others. Effects include:

Increase in the number of species of animals and plants heading toward extinction.
Loss of animal and plant habitats causes animals to move into other territories, disrupting ecosystems that are already established.
Because the behaviors of many plants, insects, and animals are dependent on temperature, a change in climate can cause an imbalance in the ecosystem itself. For example, say the availability of food for a particular insect no longer coincides with the time when the offspring of the natural predator for that insect is born. Uncontrolled by predation, the insect population booms, resulting in an overabundance of that pest. This, in turn, leads to increased stress on the foliage the insects eat, which ultimately results in a loss of food for larger animals in the food chain that also depend on those plants for sustenance.
Pests such as viruses, fungi, or parasites that usually perish at a certain low temperature no longer die off, which may lead to an increase in disease among plants, animals, and humans.
Melting of permafrost leads to flooding and greatly increases the release of carbon dioxide and methane into the atmosphere which only serves to exacerbate climate change. In addition, ancient viruses long held in stasis by the permafrost are allowed to escape into the environment.
Rainfall increases in acidity.
Earlier seasonal drying of forests leads to forest fires of increased frequency, size, and intensity. Loss of plants and trees on hillsides leaves them more vulnerable to erosion and landslides and may lead to an increased probability of property damage and loss of life.

Pachauri, R.K. and L A. Meyer (eds.) " Climate Change 2014: Synthesis Report ." Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, Geneva, Switzerland, 2014.

" Coral Reefs ." World Wildlife Fund

" Where is Earth's Water? " USGS Water Science School. United States Geological Survey.

Bittel, Jason. " The Complicated Story Behind 18,000 Dead Penguin Chicks ." onEarth Species Watch, 9 Nov 2017. Natural Resources Defense Council, Inc.

Ropert-Coudert, Yan et al. " Two Recent Massive Breeding Failures in an Adélie Penguin Colony Call for the Creation of a Marine Protected Area in D'urville Sea/Mertz. " Frontiers in Marine Science , vol. 5, no. 264, 2018, doi:10.3389/fmars.2018.00264

The Effects of Global Warming on Wildlife
A Geography and Overview of Earth's Arctic Region
What Is Sea Level and How Is It Measured?
Last Glacial Maximum - The Last Major Global Climate Change
Comparing Climate Change and Global Warming
The Next Ice Age
How Climatology Is Different From Meteorology
10 Threats to Ocean Life
What Is Physical Geography?
Megafauna Extinctions - What (or Who) Killed All the Big Mammals?
Paleoenvironmental Reconstruction
Antarctica: What's Beneath the Ice?
Global Climate Change and Evolution
Land Biomes: The World's Major Habitats
Top 6 Environmental Issues
9 Types of Marine Ecosystems

30,000+ students realised their study abroad dream with us. Take the first step today

Here’s your new year gift, one app for all your, study abroad needs, start your journey, track your progress, grow with the community and so much more.

Verification Code

An OTP has been sent to your registered mobile no. Please verify

Thanks for your comment !

Our team will review it before it's shown to our readers.

Essay on Global Warming

Updated on
Apr 27, 2024

Being able to write an essay is an integral part of mastering any language. Essays form an integral part of many academic and scholastic exams like the SAT , and UPSC amongst many others. It is a crucial evaluative part of English proficiency tests as well like IELTS , TOEFL , etc. Major essays are meant to emphasize public issues of concern that can have significant consequences on the world. To understand the concept of Global Warming and its causes and effects, we must first examine the many factors that influence the planet’s temperature and what this implies for the world’s future. Here’s an unbiased look at the essay on Global Warming and other essential related topics.

Short Essay on Global Warming and Climate Change?

Since the industrial and scientific revolutions, Earth’s resources have been gradually depleted. Furthermore, the start of the world’s population’s exponential expansion is particularly hard on the environment. Simply put, as the population’s need for consumption grows, so does the use of natural resources , as well as the waste generated by that consumption.

Climate change has been one of the most significant long-term consequences of this. Climate change is more than just the rise or fall of global temperatures; it also affects rain cycles, wind patterns, cyclone frequencies, sea levels, and other factors. It has an impact on all major life groupings on the planet.

What is Global Warming?

Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century, primarily due to the greenhouse gases released by people burning fossil fuels . The greenhouse gases consist of methane, nitrous oxide, ozone, carbon dioxide, water vapour, and chlorofluorocarbons. The weather prediction has been becoming more complex with every passing year, with seasons more indistinguishable, and the general temperatures hotter.

The number of hurricanes, cyclones, droughts, floods, etc., has risen steadily since the onset of the 21st century. The supervillain behind all these changes is Global Warming. The name is quite self-explanatory; it means the rise in the temperature of the Earth.

What are the Causes of Global Warming?

According to recent studies, many scientists believe the following are the primary four causes of global warming:

Deforestation
Greenhouse emissions
Carbon emissions per capita

Extreme global warming is causing natural disasters , which can be seen all around us. One of the causes of global warming is the extreme release of greenhouse gases that become trapped on the earth’s surface, causing the temperature to rise. Similarly, volcanoes contribute to global warming by spewing excessive CO2 into the atmosphere.

The increase in population is one of the major causes of Global Warming. This increase in population also leads to increased air pollution . Automobiles emit a lot of CO2, which remains in the atmosphere. This increase in population is also causing deforestation, which contributes to global warming.

The earth’s surface emits energy into the atmosphere in the form of heat, keeping the balance with the incoming energy. Global warming depletes the ozone layer, bringing about the end of the world. There is a clear indication that increased global warming will result in the extinction of all life on Earth’s surface.

Also Read: Land, Soil, Water, Natural Vegetation, and Wildlife Resources

Solutions for Global Warming

Of course, industries and multinational conglomerates emit more carbon than the average citizen. Nonetheless, activism and community effort are the only viable ways to slow the worsening effects of global warming. Furthermore, at the state or government level, world leaders must develop concrete plans and step-by-step programmes to ensure that no further harm is done to the environment in general.

Although we are almost too late to slow the rate of global warming, finding the right solution is critical. Everyone, from individuals to governments, must work together to find a solution to Global Warming. Some of the factors to consider are pollution control, population growth, and the use of natural resources.

One very important contribution you can make is to reduce your use of plastic. Plastic is the primary cause of global warming, and recycling it takes years. Another factor to consider is deforestation, which will aid in the control of global warming. More tree planting should be encouraged to green the environment. Certain rules should also govern industrialization. Building industries in green zones that affect plants and species should be prohibited.

Effects of Global Warming

Global warming is a real problem that many people want to disprove to gain political advantage. However, as global citizens, we must ensure that only the truth is presented in the media.

This decade has seen a significant impact from global warming. The two most common phenomena observed are glacier retreat and arctic shrinkage. Glaciers are rapidly melting. These are clear manifestations of climate change.

Another significant effect of global warming is the rise in sea level. Flooding is occurring in low-lying areas as a result of sea-level rise. Many countries have experienced extreme weather conditions. Every year, we have unusually heavy rain, extreme heat and cold, wildfires, and other natural disasters.

Similarly, as global warming continues, marine life is being severely impacted. This is causing the extinction of marine species as well as other problems. Furthermore, changes are expected in coral reefs, which will face extinction in the coming years. These effects will intensify in the coming years, effectively halting species expansion. Furthermore, humans will eventually feel the negative effects of Global Warming.

Also Read: Concept of Sustainable Development

Sample Essays on Global Warming

Here are some sample essays on Global Warming:

Essay on Global Warming Paragraph in 100 – 150 words

Global Warming is caused by the increase of carbon dioxide levels in the earth’s atmosphere and is a result of human activities that have been causing harm to our environment for the past few centuries now. Global Warming is something that can’t be ignored and steps have to be taken to tackle the situation globally. The average temperature is constantly rising by 1.5 degrees Celsius over the last few years.

The best method to prevent future damage to the earth, cutting down more forests should be banned and Afforestation should be encouraged. Start by planting trees near your homes and offices, participate in events, and teach the importance of planting trees. It is impossible to undo the damage but it is possible to stop further harm.

Essay on Global Warming in 250 Words

Over a long period, it is observed that the temperature of the earth is increasing. This affected wildlife, animals, humans, and every living organism on earth. Glaciers have been melting, and many countries have started water shortages, flooding, and erosion and all this is because of global warming.

No one can be blamed for global warming except for humans. Human activities such as gases released from power plants, transportation, and deforestation have increased gases such as carbon dioxide, CFCs, and other pollutants in the earth’s atmosphere. The main question is how can we control the current situation and build a better world for future generations. It starts with little steps by every individual.

Start using cloth bags made from sustainable materials for all shopping purposes, instead of using high-watt lights use energy-efficient bulbs, switch off the electricity, don’t waste water, abolish deforestation and encourage planting more trees. Shift the use of energy from petroleum or other fossil fuels to wind and solar energy. Instead of throwing out the old clothes donate them to someone so that it is recycled.

Donate old books, don’t waste paper. Above all, spread awareness about global warming. Every little thing a person does towards saving the earth will contribute in big or small amounts. We must learn that 1% effort is better than no effort. Pledge to take care of Mother Nature and speak up about global warming.

Essay on Global Warming in 500 Words

Global warming isn’t a prediction, it is happening! A person denying it or unaware of it is in the most simple terms complicit. Do we have another planet to live on? Unfortunately, we have been bestowed with this one planet only that can sustain life yet over the years we have turned a blind eye to the plight it is in. Global warming is not an abstract concept but a global phenomenon occurring ever so slowly even at this moment. Global Warming is a phenomenon that is occurring every minute resulting in a gradual increase in the Earth’s overall climate. Brought about by greenhouse gases that trap the solar radiation in the atmosphere, global warming can change the entire map of the earth, displacing areas, flooding many countries, and destroying multiple lifeforms. Extreme weather is a direct consequence of global warming but it is not an exhaustive consequence. There are virtually limitless effects of global warming which are all harmful to life on earth. The sea level is increasing by 0.12 inches per year worldwide. This is happening because of the melting of polar ice caps because of global warming. This has increased the frequency of floods in many lowland areas and has caused damage to coral reefs. The Arctic is one of the worst-hit areas affected by global warming. Air quality has been adversely affected and the acidity of the seawater has also increased causing severe damage to marine life forms. Severe natural disasters are brought about by global warming which has had dire effects on life and property. As long as mankind produces greenhouse gases, global warming will continue to accelerate. The consequences are felt at a much smaller scale which will increase to become drastic shortly. The power to save the day lies in the hands of humans, the need is to seize the day. Energy consumption should be reduced on an individual basis. Fuel-efficient cars and other electronics should be encouraged to reduce the wastage of energy sources. This will also improve air quality and reduce the concentration of greenhouse gases in the atmosphere. Global warming is an evil that can only be defeated when fought together. It is better late than never. If we all take steps today, we will have a much brighter future tomorrow. Global warming is the bane of our existence and various policies have come up worldwide to fight it but that is not enough. The actual difference is made when we work at an individual level to fight it. Understanding its import now is crucial before it becomes an irrevocable mistake. Exterminating global warming is of utmost importance and each one of us is as responsible for it as the next.

Also Read: Essay on Library: 100, 200 and 250 Words

Essay on Global Warming UPSC

Always hear about global warming everywhere, but do we know what it is? The evil of the worst form, global warming is a phenomenon that can affect life more fatally. Global warming refers to the increase in the earth’s temperature as a result of various human activities. The planet is gradually getting hotter and threatening the existence of lifeforms on it. Despite being relentlessly studied and researched, global warming for the majority of the population remains an abstract concept of science. It is this concept that over the years has culminated in making global warming a stark reality and not a concept covered in books. Global warming is not caused by one sole reason that can be curbed. Multifarious factors cause global warming most of which are a part of an individual’s daily existence. Burning of fuels for cooking, in vehicles, and for other conventional uses, a large amount of greenhouse gases like carbon dioxide, and methane amongst many others is produced which accelerates global warming. Rampant deforestation also results in global warming as lesser green cover results in an increased presence of carbon dioxide in the atmosphere which is a greenhouse gas. Finding a solution to global warming is of immediate importance. Global warming is a phenomenon that has to be fought unitedly. Planting more trees can be the first step that can be taken toward warding off the severe consequences of global warming. Increasing the green cover will result in regulating the carbon cycle. There should be a shift from using nonrenewable energy to renewable energy such as wind or solar energy which causes less pollution and thereby hinder the acceleration of global warming. Reducing energy needs at an individual level and not wasting energy in any form is the most important step to be taken against global warming. The warning bells are tolling to awaken us from the deep slumber of complacency we have slipped into. Humans can fight against nature and it is high time we acknowledged that. With all our scientific progress and technological inventions, fighting off the negative effects of global warming is implausible. We have to remember that we do not inherit the earth from our ancestors but borrow it from our future generations and the responsibility lies on our shoulders to bequeath them a healthy planet for life to exist.

Climate Change and Global Warming Essay

Global Warming and Climate Change are two sides of the same coin. Both are interrelated with each other and are two issues of major concern worldwide. Greenhouse gases released such as carbon dioxide, CFCs, and other pollutants in the earth’s atmosphere cause Global Warming which leads to climate change. Black holes have started to form in the ozone layer that protects the earth from harmful ultraviolet rays.

Human activities have created climate change and global warming. Industrial waste and fumes are the major contributors to global warming.

Another factor affecting is the burning of fossil fuels, deforestation and also one of the reasons for climate change. Global warming has resulted in shrinking mountain glaciers in Antarctica, Greenland, and the Arctic and causing climate change. Switching from the use of fossil fuels to energy sources like wind and solar.

When buying any electronic appliance buy the best quality with energy savings stars. Don’t waste water and encourage rainwater harvesting in your community.

Tips to Write an Essay

Writing an effective essay needs skills that few people possess and even fewer know how to implement. While writing an essay can be an assiduous task that can be unnerving at times, some key pointers can be inculcated to draft a successful essay. These involve focusing on the structure of the essay, planning it out well, and emphasizing crucial details.

Mentioned below are some pointers that can help you write better structure and more thoughtful essays that will get across to your readers:

Prepare an outline for the essay to ensure continuity and relevance and no break in the structure of the essay
Decide on a thesis statement that will form the basis of your essay. It will be the point of your essay and help readers understand your contention
Follow the structure of an introduction, a detailed body followed by a conclusion so that the readers can comprehend the essay in a particular manner without any dissonance.
Make your beginning catchy and include solutions in your conclusion to make the essay insightful and lucrative to read
Reread before putting it out and add your flair to the essay to make it more personal and thereby unique and intriguing for readers

Also Read: I Love My India Essay: 100 and 500+ Words in English for School Students

Ans. Both natural and man-made factors contribute to global warming. The natural one also contains methane gas, volcanic eruptions, and greenhouse gases. Deforestation, mining, livestock raising, burning fossil fuels, and other man-made causes are next.

Ans. The government and the general public can work together to stop global warming. Trees must be planted more often, and deforestation must be prohibited. Auto usage needs to be curbed, and recycling needs to be promoted.

Ans. Switching to renewable energy sources , adopting sustainable farming, transportation, and energy methods, and conserving water and other natural resources.

Relevant Blogs

For more information on such interesting topics, visit our essay writing page and follow Leverage Edu.

Digvijay Singh

Having 2+ years of experience in educational content writing, withholding a Bachelor's in Physical Education and Sports Science and a strong interest in writing educational content for students enrolled in domestic and foreign study abroad programmes. I believe in offering a distinct viewpoint to the table, to help students deal with the complexities of both domestic and foreign educational systems. Through engaging storytelling and insightful analysis, I aim to inspire my readers to embark on their educational journeys, whether abroad or at home, and to make the most of every learning opportunity that comes their way.

8 Universities with higher ROI than IITs and IIMs

Grab this one-time opportunity to download this ebook

Connect With Us

30,000+ students realised their study abroad dream with us. take the first step today..

Resend OTP in

Need help with?

Study abroad.

UK, Canada, US & More

IELTS, GRE, GMAT & More

Scholarship, Loans & Forex

Country Preference

New Zealand

Which English test are you planning to take?

Which academic test are you planning to take.

Not Sure yet

When are you planning to take the exam?

Already booked my exam slot

Within 2 Months

Want to learn about the test

Which Degree do you wish to pursue?

When do you want to start studying abroad.

September 2024

January 2025

What is your budget to study abroad?

How would you describe this article ?

Please rate this article

We would like to hear more.

ENCYCLOPEDIC ENTRY

Global warming.

The causes, effects, and complexities of global warming are important to understand so that we can fight for the health of our planet.

Earth Science, Climatology

Tennessee Power Plant

Ash spews from a coal-fueled power plant in New Johnsonville, Tennessee, United States.

Photograph by Emory Kristof/ National Geographic

Global warming is the long-term warming of the planet’s overall temperature. Though this warming trend has been going on for a long time, its pace has significantly increased in the last hundred years due to the burning of fossil fuels . As the human population has increased, so has the volume of fossil fuels burned. Fossil fuels include coal, oil, and natural gas, and burning them causes what is known as the “greenhouse effect” in Earth’s atmosphere.

The greenhouse effect is when the sun’s rays penetrate the atmosphere, but when that heat is reflected off the surface cannot escape back into space. Gases produced by the burning of fossil fuels prevent the heat from leaving the atmosphere. These greenhouse gasses are carbon dioxide , chlorofluorocarbons, water vapor , methane , and nitrous oxide . The excess heat in the atmosphere has caused the average global temperature to rise overtime, otherwise known as global warming.

Global warming has presented another issue called climate change. Sometimes these phrases are used interchangeably, however, they are different. Climate change refers to changes in weather patterns and growing seasons around the world. It also refers to sea level rise caused by the expansion of warmer seas and melting ice sheets and glaciers . Global warming causes climate change, which poses a serious threat to life on Earth in the forms of widespread flooding and extreme weather. Scientists continue to study global warming and its impact on Earth.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, last updated.

February 21, 2024

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

Share full article

The Science of Climate Change Explained: Facts, Evidence and Proof

Definitive answers to the big questions.

Credit... Photo Illustration by Andrea D'Aquino

Supported by

By Julia Rosen

Ms. Rosen is a journalist with a Ph.D. in geology. Her research involved studying ice cores from Greenland and Antarctica to understand past climate changes.

Published April 19, 2021 Updated Nov. 6, 2021

The science of climate change is more solid and widely agreed upon than you might think. But the scope of the topic, as well as rampant disinformation, can make it hard to separate fact from fiction. Here, we’ve done our best to present you with not only the most accurate scientific information, but also an explanation of how we know it.

How do we know climate change is really happening?

How much agreement is there among scientists about climate change, do we really only have 150 years of climate data how is that enough to tell us about centuries of change, how do we know climate change is caused by humans, since greenhouse gases occur naturally, how do we know they’re causing earth’s temperature to rise, why should we be worried that the planet has warmed 2°f since the 1800s, is climate change a part of the planet’s natural warming and cooling cycles, how do we know global warming is not because of the sun or volcanoes, how can winters and certain places be getting colder if the planet is warming, wildfires and bad weather have always happened. how do we know there’s a connection to climate change, how bad are the effects of climate change going to be, what will it cost to do something about climate change, versus doing nothing.

Climate change is often cast as a prediction made by complicated computer models. But the scientific basis for climate change is much broader, and models are actually only one part of it (and, for what it’s worth, they’re surprisingly accurate ).

For more than a century , scientists have understood the basic physics behind why greenhouse gases like carbon dioxide cause warming. These gases make up just a small fraction of the atmosphere but exert outsized control on Earth’s climate by trapping some of the planet’s heat before it escapes into space. This greenhouse effect is important: It’s why a planet so far from the sun has liquid water and life!

However, during the Industrial Revolution, people started burning coal and other fossil fuels to power factories, smelters and steam engines, which added more greenhouse gases to the atmosphere. Ever since, human activities have been heating the planet.

We know this is true thanks to an overwhelming body of evidence that begins with temperature measurements taken at weather stations and on ships starting in the mid-1800s. Later, scientists began tracking surface temperatures with satellites and looking for clues about climate change in geologic records. Together, these data all tell the same story: Earth is getting hotter.

Average global temperatures have increased by 2.2 degrees Fahrenheit, or 1.2 degrees Celsius, since 1880, with the greatest changes happening in the late 20th century. Land areas have warmed more than the sea surface and the Arctic has warmed the most — by more than 4 degrees Fahrenheit just since the 1960s. Temperature extremes have also shifted. In the United States, daily record highs now outnumber record lows two-to-one.

Where it was cooler or warmer in 2020 compared with the middle of the 20th century

This warming is unprecedented in recent geologic history. A famous illustration, first published in 1998 and often called the hockey-stick graph, shows how temperatures remained fairly flat for centuries (the shaft of the stick) before turning sharply upward (the blade). It’s based on data from tree rings, ice cores and other natural indicators. And the basic picture , which has withstood decades of scrutiny from climate scientists and contrarians alike, shows that Earth is hotter today than it’s been in at least 1,000 years, and probably much longer.

In fact, surface temperatures actually mask the true scale of climate change, because the ocean has absorbed 90 percent of the heat trapped by greenhouse gases . Measurements collected over the last six decades by oceanographic expeditions and networks of floating instruments show that every layer of the ocean is warming up. According to one study , the ocean has absorbed as much heat between 1997 and 2015 as it did in the previous 130 years.

We also know that climate change is happening because we see the effects everywhere. Ice sheets and glaciers are shrinking while sea levels are rising. Arctic sea ice is disappearing. In the spring, snow melts sooner and plants flower earlier. Animals are moving to higher elevations and latitudes to find cooler conditions. And droughts, floods and wildfires have all gotten more extreme. Models predicted many of these changes, but observations show they are now coming to pass.

There’s no denying that scientists love a good, old-fashioned argument. But when it comes to climate change, there is virtually no debate: Numerous studies have found that more than 90 percent of scientists who study Earth’s climate agree that the planet is warming and that humans are the primary cause. Most major scientific bodies, from NASA to the World Meteorological Organization , endorse this view. That’s an astounding level of consensus given the contrarian, competitive nature of the scientific enterprise, where questions like what killed the dinosaurs remain bitterly contested .

Scientific agreement about climate change started to emerge in the late 1980s, when the influence of human-caused warming began to rise above natural climate variability. By 1991, two-thirds of earth and atmospheric scientists surveyed for an early consensus study said that they accepted the idea of anthropogenic global warming. And by 1995, the Intergovernmental Panel on Climate Change, a famously conservative body that periodically takes stock of the state of scientific knowledge, concluded that “the balance of evidence suggests that there is a discernible human influence on global climate.” Currently, more than 97 percent of publishing climate scientists agree on the existence and cause of climate change (as does nearly 60 percent of the general population of the United States).

So where did we get the idea that there’s still debate about climate change? A lot of it came from coordinated messaging campaigns by companies and politicians that opposed climate action. Many pushed the narrative that scientists still hadn’t made up their minds about climate change, even though that was misleading. Frank Luntz, a Republican consultant, explained the rationale in an infamous 2002 memo to conservative lawmakers: “Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly,” he wrote. Questioning consensus remains a common talking point today, and the 97 percent figure has become something of a lightning rod .

To bolster the falsehood of lingering scientific doubt, some people have pointed to things like the Global Warming Petition Project, which urged the United States government to reject the Kyoto Protocol of 1997, an early international climate agreement. The petition proclaimed that climate change wasn’t happening, and even if it were, it wouldn’t be bad for humanity. Since 1998, more than 30,000 people with science degrees have signed it. However, nearly 90 percent of them studied something other than Earth, atmospheric or environmental science, and the signatories included just 39 climatologists. Most were engineers, doctors, and others whose training had little to do with the physics of the climate system.

A few well-known researchers remain opposed to the scientific consensus. Some, like Willie Soon, a researcher affiliated with the Harvard-Smithsonian Center for Astrophysics, have ties to the fossil fuel industry . Others do not, but their assertions have not held up under the weight of evidence. At least one prominent skeptic, the physicist Richard Muller, changed his mind after reassessing historical temperature data as part of the Berkeley Earth project. His team’s findings essentially confirmed the results he had set out to investigate, and he came away firmly convinced that human activities were warming the planet. “Call me a converted skeptic,” he wrote in an Op-Ed for the Times in 2012.

Mr. Luntz, the Republican pollster, has also reversed his position on climate change and now advises politicians on how to motivate climate action.

A final note on uncertainty: Denialists often use it as evidence that climate science isn’t settled. However, in science, uncertainty doesn’t imply a lack of knowledge. Rather, it’s a measure of how well something is known. In the case of climate change, scientists have found a range of possible future changes in temperature, precipitation and other important variables — which will depend largely on how quickly we reduce emissions. But uncertainty does not undermine their confidence that climate change is real and that people are causing it.

Earth’s climate is inherently variable. Some years are hot and others are cold, some decades bring more hurricanes than others, some ancient droughts spanned the better part of centuries. Glacial cycles operate over many millenniums. So how can scientists look at data collected over a relatively short period of time and conclude that humans are warming the planet? The answer is that the instrumental temperature data that we have tells us a lot, but it’s not all we have to go on.

Historical records stretch back to the 1880s (and often before), when people began to regularly measure temperatures at weather stations and on ships as they traversed the world’s oceans. These data show a clear warming trend during the 20th century.

Global average temperature compared with the middle of the 20th century

+0.75°C

–0.25°

Some have questioned whether these records could be skewed, for instance, by the fact that a disproportionate number of weather stations are near cities, which tend to be hotter than surrounding areas as a result of the so-called urban heat island effect. However, researchers regularly correct for these potential biases when reconstructing global temperatures. In addition, warming is corroborated by independent data like satellite observations, which cover the whole planet, and other ways of measuring temperature changes.

Much has also been made of the small dips and pauses that punctuate the rising temperature trend of the last 150 years. But these are just the result of natural climate variability or other human activities that temporarily counteract greenhouse warming. For instance, in the mid-1900s, internal climate dynamics and light-blocking pollution from coal-fired power plants halted global warming for a few decades. (Eventually, rising greenhouse gases and pollution-control laws caused the planet to start heating up again.) Likewise, the so-called warming hiatus of the 2000s was partly a result of natural climate variability that allowed more heat to enter the ocean rather than warm the atmosphere. The years since have been the hottest on record .

Still, could the entire 20th century just be one big natural climate wiggle? To address that question, we can look at other kinds of data that give a longer perspective. Researchers have used geologic records like tree rings, ice cores, corals and sediments that preserve information about prehistoric climates to extend the climate record. The resulting picture of global temperature change is basically flat for centuries, then turns sharply upward over the last 150 years. It has been a target of climate denialists for decades. However, study after study has confirmed the results , which show that the planet hasn’t been this hot in at least 1,000 years, and probably longer.

Scientists have studied past climate changes to understand the factors that can cause the planet to warm or cool. The big ones are changes in solar energy, ocean circulation, volcanic activity and the amount of greenhouse gases in the atmosphere. And they have each played a role at times.

For example, 300 years ago, a combination of reduced solar output and increased volcanic activity cooled parts of the planet enough that Londoners regularly ice skated on the Thames . About 12,000 years ago, major changes in Atlantic circulation plunged the Northern Hemisphere into a frigid state. And 56 million years ago, a giant burst of greenhouse gases, from volcanic activity or vast deposits of methane (or both), abruptly warmed the planet by at least 9 degrees Fahrenheit, scrambling the climate, choking the oceans and triggering mass extinctions.

In trying to determine the cause of current climate changes, scientists have looked at all of these factors . The first three have varied a bit over the last few centuries and they have quite likely had modest effects on climate , particularly before 1950. But they cannot account for the planet’s rapidly rising temperature, especially in the second half of the 20th century, when solar output actually declined and volcanic eruptions exerted a cooling effect.

That warming is best explained by rising greenhouse gas concentrations . Greenhouse gases have a powerful effect on climate (see the next question for why). And since the Industrial Revolution, humans have been adding more of them to the atmosphere, primarily by extracting and burning fossil fuels like coal, oil and gas, which releases carbon dioxide.

Bubbles of ancient air trapped in ice show that, before about 1750, the concentration of carbon dioxide in the atmosphere was roughly 280 parts per million. It began to rise slowly and crossed the 300 p.p.m. threshold around 1900. CO2 levels then accelerated as cars and electricity became big parts of modern life, recently topping 420 p.p.m . The concentration of methane, the second most important greenhouse gas, has more than doubled. We’re now emitting carbon much faster than it was released 56 million years ago .

30 billion metric tons

Carbon dioxide emitted worldwide 1850-2017

Rest of world

Other developed

European Union

Developed economies

Other countries

United States

E.U. and U.K.

These rapid increases in greenhouse gases have caused the climate to warm abruptly. In fact, climate models suggest that greenhouse warming can explain virtually all of the temperature change since 1950. According to the most recent report by the Intergovernmental Panel on Climate Change, which assesses published scientific literature, natural drivers and internal climate variability can only explain a small fraction of late-20th century warming.

Another study put it this way: The odds of current warming occurring without anthropogenic greenhouse gas emissions are less than 1 in 100,000 .

But greenhouse gases aren’t the only climate-altering compounds people put into the air. Burning fossil fuels also produces particulate pollution that reflects sunlight and cools the planet. Scientists estimate that this pollution has masked up to half of the greenhouse warming we would have otherwise experienced.

Greenhouse gases like water vapor and carbon dioxide serve an important role in the climate. Without them, Earth would be far too cold to maintain liquid water and humans would not exist!

Here’s how it works: the planet’s temperature is basically a function of the energy the Earth absorbs from the sun (which heats it up) and the energy Earth emits to space as infrared radiation (which cools it down). Because of their molecular structure, greenhouse gases temporarily absorb some of that outgoing infrared radiation and then re-emit it in all directions, sending some of that energy back toward the surface and heating the planet . Scientists have understood this process since the 1850s .

Greenhouse gas concentrations have varied naturally in the past. Over millions of years, atmospheric CO2 levels have changed depending on how much of the gas volcanoes belched into the air and how much got removed through geologic processes. On time scales of hundreds to thousands of years, concentrations have changed as carbon has cycled between the ocean, soil and air.

Today, however, we are the ones causing CO2 levels to increase at an unprecedented pace by taking ancient carbon from geologic deposits of fossil fuels and putting it into the atmosphere when we burn them. Since 1750, carbon dioxide concentrations have increased by almost 50 percent. Methane and nitrous oxide, other important anthropogenic greenhouse gases that are released mainly by agricultural activities, have also spiked over the last 250 years.

We know based on the physics described above that this should cause the climate to warm. We also see certain telltale “fingerprints” of greenhouse warming. For example, nights are warming even faster than days because greenhouse gases don’t go away when the sun sets. And upper layers of the atmosphere have actually cooled, because more energy is being trapped by greenhouse gases in the lower atmosphere.

We also know that we are the cause of rising greenhouse gas concentrations — and not just because we can measure the CO2 coming out of tailpipes and smokestacks. We can see it in the chemical signature of the carbon in CO2.

Carbon comes in three different masses: 12, 13 and 14. Things made of organic matter (including fossil fuels) tend to have relatively less carbon-13. Volcanoes tend to produce CO2 with relatively more carbon-13. And over the last century, the carbon in atmospheric CO2 has gotten lighter, pointing to an organic source.

We can tell it’s old organic matter by looking for carbon-14, which is radioactive and decays over time. Fossil fuels are too ancient to have any carbon-14 left in them, so if they were behind rising CO2 levels, you would expect the amount of carbon-14 in the atmosphere to drop, which is exactly what the data show .

It’s important to note that water vapor is the most abundant greenhouse gas in the atmosphere. However, it does not cause warming; instead it responds to it . That’s because warmer air holds more moisture, which creates a snowball effect in which human-caused warming allows the atmosphere to hold more water vapor and further amplifies climate change. This so-called feedback cycle has doubled the warming caused by anthropogenic greenhouse gas emissions.

A common source of confusion when it comes to climate change is the difference between weather and climate. Weather is the constantly changing set of meteorological conditions that we experience when we step outside, whereas climate is the long-term average of those conditions, usually calculated over a 30-year period. Or, as some say: Weather is your mood and climate is your personality.

So while 2 degrees Fahrenheit doesn’t represent a big change in the weather, it’s a huge change in climate. As we’ve already seen, it’s enough to melt ice and raise sea levels, to shift rainfall patterns around the world and to reorganize ecosystems, sending animals scurrying toward cooler habitats and killing trees by the millions.

It’s also important to remember that two degrees represents the global average, and many parts of the world have already warmed by more than that. For example, land areas have warmed about twice as much as the sea surface. And the Arctic has warmed by about 5 degrees. That’s because the loss of snow and ice at high latitudes allows the ground to absorb more energy, causing additional heating on top of greenhouse warming.

Relatively small long-term changes in climate averages also shift extremes in significant ways. For instance, heat waves have always happened, but they have shattered records in recent years. In June of 2020, a town in Siberia registered temperatures of 100 degrees . And in Australia, meteorologists have added a new color to their weather maps to show areas where temperatures exceed 125 degrees. Rising sea levels have also increased the risk of flooding because of storm surges and high tides. These are the foreshocks of climate change.

And we are in for more changes in the future — up to 9 degrees Fahrenheit of average global warming by the end of the century, in the worst-case scenario . For reference, the difference in global average temperatures between now and the peak of the last ice age, when ice sheets covered large parts of North America and Europe, is about 11 degrees Fahrenheit.

Under the Paris Climate Agreement, which President Biden recently rejoined, countries have agreed to try to limit total warming to between 1.5 and 2 degrees Celsius, or 2.7 and 3.6 degrees Fahrenheit, since preindustrial times. And even this narrow range has huge implications . According to scientific studies, the difference between 2.7 and 3.6 degrees Fahrenheit will very likely mean the difference between coral reefs hanging on or going extinct, and between summer sea ice persisting in the Arctic or disappearing completely. It will also determine how many millions of people suffer from water scarcity and crop failures, and how many are driven from their homes by rising seas. In other words, one degree Fahrenheit makes a world of difference.

Earth’s climate has always changed. Hundreds of millions of years ago, the entire planet froze . Fifty million years ago, alligators lived in what we now call the Arctic . And for the last 2.6 million years, the planet has cycled between ice ages when the planet was up to 11 degrees cooler and ice sheets covered much of North America and Europe, and milder interglacial periods like the one we’re in now.

Climate denialists often point to these natural climate changes as a way to cast doubt on the idea that humans are causing climate to change today. However, that argument rests on a logical fallacy. It’s like “seeing a murdered body and concluding that people have died of natural causes in the past, so the murder victim must also have died of natural causes,” a team of social scientists wrote in The Debunking Handbook , which explains the misinformation strategies behind many climate myths.

Indeed, we know that different mechanisms caused the climate to change in the past. Glacial cycles, for example, were triggered by periodic variations in Earth’s orbit , which take place over tens of thousands of years and change how solar energy gets distributed around the globe and across the seasons.

These orbital variations don’t affect the planet’s temperature much on their own. But they set off a cascade of other changes in the climate system; for instance, growing or melting vast Northern Hemisphere ice sheets and altering ocean circulation. These changes, in turn, affect climate by altering the amount of snow and ice, which reflect sunlight, and by changing greenhouse gas concentrations. This is actually part of how we know that greenhouse gases have the ability to significantly affect Earth’s temperature.

For at least the last 800,000 years , atmospheric CO2 concentrations oscillated between about 180 parts per million during ice ages and about 280 p.p.m. during warmer periods, as carbon moved between oceans, forests, soils and the atmosphere. These changes occurred in lock step with global temperatures, and are a major reason the entire planet warmed and cooled during glacial cycles, not just the frozen poles.

Today, however, CO2 levels have soared to 420 p.p.m. — the highest they’ve been in at least three million years . The concentration of CO2 is also increasing about 100 times faster than it did at the end of the last ice age. This suggests something else is going on, and we know what it is: Since the Industrial Revolution, humans have been burning fossil fuels and releasing greenhouse gases that are heating the planet now (see Question 5 for more details on how we know this, and Questions 4 and 8 for how we know that other natural forces aren’t to blame).

Over the next century or two, societies and ecosystems will experience the consequences of this climate change. But our emissions will have even more lasting geologic impacts: According to some studies, greenhouse gas levels may have already warmed the planet enough to delay the onset of the next glacial cycle for at least an additional 50,000 years.

The sun is the ultimate source of energy in Earth’s climate system, so it’s a natural candidate for causing climate change. And solar activity has certainly changed over time. We know from satellite measurements and other astronomical observations that the sun’s output changes on 11-year cycles. Geologic records and sunspot numbers, which astronomers have tracked for centuries, also show long-term variations in the sun’s activity, including some exceptionally quiet periods in the late 1600s and early 1800s.

We know that, from 1900 until the 1950s, solar irradiance increased. And studies suggest that this had a modest effect on early 20th century climate, explaining up to 10 percent of the warming that’s occurred since the late 1800s. However, in the second half of the century, when the most warming occurred, solar activity actually declined . This disparity is one of the main reasons we know that the sun is not the driving force behind climate change.

Another reason we know that solar activity hasn’t caused recent warming is that, if it had, all the layers of the atmosphere should be heating up. Instead, data show that the upper atmosphere has actually cooled in recent decades — a hallmark of greenhouse warming .

So how about volcanoes? Eruptions cool the planet by injecting ash and aerosol particles into the atmosphere that reflect sunlight. We’ve observed this effect in the years following large eruptions. There are also some notable historical examples, like when Iceland’s Laki volcano erupted in 1783, causing widespread crop failures in Europe and beyond, and the “ year without a summer ,” which followed the 1815 eruption of Mount Tambora in Indonesia.

Since volcanoes mainly act as climate coolers, they can’t really explain recent warming. However, scientists say that they may also have contributed slightly to rising temperatures in the early 20th century. That’s because there were several large eruptions in the late 1800s that cooled the planet, followed by a few decades with no major volcanic events when warming caught up. During the second half of the 20th century, though, several big eruptions occurred as the planet was heating up fast. If anything, they temporarily masked some amount of human-caused warming.

The second way volcanoes can impact climate is by emitting carbon dioxide. This is important on time scales of millions of years — it’s what keeps the planet habitable (see Question 5 for more on the greenhouse effect). But by comparison to modern anthropogenic emissions, even big eruptions like Krakatoa and Mount St. Helens are just a drop in the bucket. After all, they last only a few hours or days, while we burn fossil fuels 24-7. Studies suggest that, today, volcanoes account for 1 to 2 percent of total CO2 emissions.

When a big snowstorm hits the United States, climate denialists can try to cite it as proof that climate change isn’t happening. In 2015, Senator James Inhofe, an Oklahoma Republican, famously lobbed a snowball in the Senate as he denounced climate science. But these events don’t actually disprove climate change.

While there have been some memorable storms in recent years, winters are actually warming across the world. In the United States, average temperatures in December, January and February have increased by about 2.5 degrees this century.

On the flip side, record cold days are becoming less common than record warm days. In the United States, record highs now outnumber record lows two-to-one . And ever-smaller areas of the country experience extremely cold winter temperatures . (The same trends are happening globally.)

So what’s with the blizzards? Weather always varies, so it’s no surprise that we still have severe winter storms even as average temperatures rise. However, some studies suggest that climate change may be to blame. One possibility is that rapid Arctic warming has affected atmospheric circulation, including the fast-flowing, high-altitude air that usually swirls over the North Pole (a.k.a. the Polar Vortex ). Some studies suggest that these changes are bringing more frigid temperatures to lower latitudes and causing weather systems to stall , allowing storms to produce more snowfall. This may explain what we’ve experienced in the U.S. over the past few decades, as well as a wintertime cooling trend in Siberia , although exactly how the Arctic affects global weather remains a topic of ongoing scientific debate .

Climate change may also explain the apparent paradox behind some of the other places on Earth that haven’t warmed much. For instance, a splotch of water in the North Atlantic has cooled in recent years, and scientists say they suspect that may be because ocean circulation is slowing as a result of freshwater streaming off a melting Greenland . If this circulation grinds almost to a halt, as it’s done in the geologic past, it would alter weather patterns around the world.

Not all cold weather stems from some counterintuitive consequence of climate change. But it’s a good reminder that Earth’s climate system is complex and chaotic, so the effects of human-caused changes will play out differently in different places. That’s why “global warming” is a bit of an oversimplification. Instead, some scientists have suggested that the phenomenon of human-caused climate change would more aptly be called “ global weirding .”

Extreme weather and natural disasters are part of life on Earth — just ask the dinosaurs. But there is good evidence that climate change has increased the frequency and severity of certain phenomena like heat waves, droughts and floods. Recent research has also allowed scientists to identify the influence of climate change on specific events.

Let’s start with heat waves . Studies show that stretches of abnormally high temperatures now happen about five times more often than they would without climate change, and they last longer, too. Climate models project that, by the 2040s, heat waves will be about 12 times more frequent. And that’s concerning since extreme heat often causes increased hospitalizations and deaths, particularly among older people and those with underlying health conditions. In the summer of 2003, for example, a heat wave caused an estimated 70,000 excess deaths across Europe. (Human-caused warming amplified the death toll .)

Climate change has also exacerbated droughts , primarily by increasing evaporation. Droughts occur naturally because of random climate variability and factors like whether El Niño or La Niña conditions prevail in the tropical Pacific. But some researchers have found evidence that greenhouse warming has been affecting droughts since even before the Dust Bowl . And it continues to do so today. According to one analysis , the drought that afflicted the American Southwest from 2000 to 2018 was almost 50 percent more severe because of climate change. It was the worst drought the region had experienced in more than 1,000 years.

Rising temperatures have also increased the intensity of heavy precipitation events and the flooding that often follows. For example, studies have found that, because warmer air holds more moisture, Hurricane Harvey, which struck Houston in 2017, dropped between 15 and 40 percent more rainfall than it would have without climate change.

It’s still unclear whether climate change is changing the overall frequency of hurricanes, but it is making them stronger . And warming appears to favor certain kinds of weather patterns, like the “ Midwest Water Hose ” events that caused devastating flooding across the Midwest in 2019 .

It’s important to remember that in most natural disasters, there are multiple factors at play. For instance, the 2019 Midwest floods occurred after a recent cold snap had frozen the ground solid, preventing the soil from absorbing rainwater and increasing runoff into the Missouri and Mississippi Rivers. These waterways have also been reshaped by levees and other forms of river engineering, some of which failed in the floods.

Wildfires are another phenomenon with multiple causes. In many places, fire risk has increased because humans have aggressively fought natural fires and prevented Indigenous peoples from carrying out traditional burning practices. This has allowed fuel to accumulate that makes current fires worse .

However, climate change still plays a major role by heating and drying forests, turning them into tinderboxes. Studies show that warming is the driving factor behind the recent increases in wildfires; one analysis found that climate change is responsible for doubling the area burned across the American West between 1984 and 2015. And researchers say that warming will only make fires bigger and more dangerous in the future.

It depends on how aggressively we act to address climate change. If we continue with business as usual, by the end of the century, it will be too hot to go outside during heat waves in the Middle East and South Asia . Droughts will grip Central America, the Mediterranean and southern Africa. And many island nations and low-lying areas, from Texas to Bangladesh, will be overtaken by rising seas. Conversely, climate change could bring welcome warming and extended growing seasons to the upper Midwest , Canada, the Nordic countries and Russia . Farther north, however, the loss of snow, ice and permafrost will upend the traditions of Indigenous peoples and threaten infrastructure.

It’s complicated, but the underlying message is simple: unchecked climate change will likely exacerbate existing inequalities . At a national level, poorer countries will be hit hardest, even though they have historically emitted only a fraction of the greenhouse gases that cause warming. That’s because many less developed countries tend to be in tropical regions where additional warming will make the climate increasingly intolerable for humans and crops. These nations also often have greater vulnerabilities, like large coastal populations and people living in improvised housing that is easily damaged in storms. And they have fewer resources to adapt, which will require expensive measures like redesigning cities, engineering coastlines and changing how people grow food.

Already, between 1961 and 2000, climate change appears to have harmed the economies of the poorest countries while boosting the fortunes of the wealthiest nations that have done the most to cause the problem, making the global wealth gap 25 percent bigger than it would otherwise have been. Similarly, the Global Climate Risk Index found that lower income countries — like Myanmar, Haiti and Nepal — rank high on the list of nations most affected by extreme weather between 1999 and 2018. Climate change has also contributed to increased human migration, which is expected to increase significantly .

Even within wealthy countries, the poor and marginalized will suffer the most. People with more resources have greater buffers, like air-conditioners to keep their houses cool during dangerous heat waves, and the means to pay the resulting energy bills. They also have an easier time evacuating their homes before disasters, and recovering afterward. Lower income people have fewer of these advantages, and they are also more likely to live in hotter neighborhoods and work outdoors, where they face the brunt of climate change.

These inequalities will play out on an individual, community, and regional level. A 2017 analysis of the U.S. found that, under business as usual, the poorest one-third of counties, which are concentrated in the South, will experience damages totaling as much as 20 percent of gross domestic product, while others, mostly in the northern part of the country, will see modest economic gains. Solomon Hsiang, an economist at University of California, Berkeley, and the lead author of the study, has said that climate change “may result in the largest transfer of wealth from the poor to the rich in the country’s history.”

Even the climate “winners” will not be immune from all climate impacts, though. Desirable locations will face an influx of migrants. And as the coronavirus pandemic has demonstrated, disasters in one place quickly ripple across our globalized economy. For instance, scientists expect climate change to increase the odds of multiple crop failures occurring at the same time in different places, throwing the world into a food crisis .

On top of that, warmer weather is aiding the spread of infectious diseases and the vectors that transmit them, like ticks and mosquitoes . Research has also identified troubling correlations between rising temperatures and increased interpersonal violence , and climate change is widely recognized as a “threat multiplier” that increases the odds of larger conflicts within and between countries. In other words, climate change will bring many changes that no amount of money can stop. What could help is taking action to limit warming.

One of the most common arguments against taking aggressive action to combat climate change is that doing so will kill jobs and cripple the economy. But this implies that there’s an alternative in which we pay nothing for climate change. And unfortunately, there isn’t. In reality, not tackling climate change will cost a lot , and cause enormous human suffering and ecological damage, while transitioning to a greener economy would benefit many people and ecosystems around the world.

Let’s start with how much it will cost to address climate change. To keep warming well below 2 degrees Celsius, the goal of the Paris Climate Agreement, society will have to reach net zero greenhouse gas emissions by the middle of this century. That will require significant investments in things like renewable energy, electric cars and charging infrastructure, not to mention efforts to adapt to hotter temperatures, rising sea-levels and other unavoidable effects of current climate changes. And we’ll have to make changes fast.

Estimates of the cost vary widely. One recent study found that keeping warming to 2 degrees Celsius would require a total investment of between $4 trillion and $60 trillion, with a median estimate of $16 trillion, while keeping warming to 1.5 degrees Celsius could cost between $10 trillion and $100 trillion, with a median estimate of $30 trillion. (For reference, the entire world economy was about $88 trillion in 2019.) Other studies have found that reaching net zero will require annual investments ranging from less than 1.5 percent of global gross domestic product to as much as 4 percent . That’s a lot, but within the range of historical energy investments in countries like the U.S.

Now, let’s consider the costs of unchecked climate change, which will fall hardest on the most vulnerable. These include damage to property and infrastructure from sea-level rise and extreme weather, death and sickness linked to natural disasters, pollution and infectious disease, reduced agricultural yields and lost labor productivity because of rising temperatures, decreased water availability and increased energy costs, and species extinction and habitat destruction. Dr. Hsiang, the U.C. Berkeley economist, describes it as “death by a thousand cuts.”

As a result, climate damages are hard to quantify. Moody’s Analytics estimates that even 2 degrees Celsius of warming will cost the world $69 trillion by 2100, and economists expect the toll to keep rising with the temperature. In a recent survey , economists estimated the cost would equal 5 percent of global G.D.P. at 3 degrees Celsius of warming (our trajectory under current policies) and 10 percent for 5 degrees Celsius. Other research indicates that, if current warming trends continue, global G.D.P. per capita will decrease between 7 percent and 23 percent by the end of the century — an economic blow equivalent to multiple coronavirus pandemics every year. And some fear these are vast underestimates .

Already, studies suggest that climate change has slashed incomes in the poorest countries by as much as 30 percent and reduced global agricultural productivity by 21 percent since 1961. Extreme weather events have also racked up a large bill. In 2020, in the United States alone, climate-related disasters like hurricanes, droughts, and wildfires caused nearly $100 billion in damages to businesses, property and infrastructure, compared to an average of $18 billion per year in the 1980s.

Given the steep price of inaction, many economists say that addressing climate change is a better deal . It’s like that old saying: an ounce of prevention is worth a pound of cure. In this case, limiting warming will greatly reduce future damage and inequality caused by climate change. It will also produce so-called co-benefits, like saving one million lives every year by reducing air pollution, and millions more from eating healthier, climate-friendly diets. Some studies even find that meeting the Paris Agreement goals could create jobs and increase global G.D.P . And, of course, reining in climate change will spare many species and ecosystems upon which humans depend — and which many people believe to have their own innate value.

The challenge is that we need to reduce emissions now to avoid damages later, which requires big investments over the next few decades. And the longer we delay, the more we will pay to meet the Paris goals. One recent analysis found that reaching net-zero by 2050 would cost the U.S. almost twice as much if we waited until 2030 instead of acting now. But even if we miss the Paris target, the economics still make a strong case for climate action, because every additional degree of warming will cost us more — in dollars, and in lives.

Veronica Penney contributed reporting.

Illustration photographs by Esther Horvath, Max Whittaker, David Maurice Smith and Talia Herman for The New York Times; Esther Horvath/Alfred-Wegener-Institut

An earlier version of this article misidentified the authors of The Debunking Handbook. It was written by social scientists who study climate communication, not a team of climate scientists.

How we handle corrections

What’s Up in Space and Astronomy

Keep track of things going on in our solar system and all around the universe..

Never miss an eclipse, a meteor shower, a rocket launch or any other 2024 event that’s out of this world with our space and astronomy calendar .

A dramatic blast from the sun set off the highest-level geomagnetic storm in Earth’s atmosphere, making the northern lights visible around the world .

With the help of Google Cloud, scientists who hunt killer asteroids churned through hundreds of thousands of images of the night sky to reveal 27,500 overlooked space rocks in the solar system .

A celestial image, an Impressionistic swirl of color in the center of the Milky Way, represents a first step toward understanding the role of magnetic fields in the cycle of stellar death and rebirth.

Scientists may have discovered a major flaw in their understanding of dark energy, a mysterious cosmic force . That could be good news for the fate of the universe.

Is Pluto a planet? And what is a planet, anyway? Test your knowledge here .

Are there positive benefits from global warming?

Yes, there will probably be some short-term and long-term benefits from global warming. For example, the flip side of increased mortality from heat waves may be decreased mortality from cold waves.

In the short term, farmers in some regions may benefit from the earlier onset of spring and from a longer warm season that is suitable for growing crops. Also, studies show that, up to a certain point, crops and other plants grow better in the presence of higher carbon dioxide levels and seem to be more drought-tolerant. [ 1 ] But this benefit is a two-edged sword: weeds, many invasive plant species, and insect pests will also thrive in a warmer world. Water availability will be impacted in drier agricultural areas that need irrigation. At some point, the benefits to crops of increased carbon dioxide will likely be overwhelmed by the negative impacts of heat stress and drought.

In July 2017, Finnish icebreaker, MSV Nordica , photographed here in 2011, set a new record for the earliest transit through the Northwest Passage. Photo CC license by JV Virta .

In the long term, shipping commerce will benefit from the opening of the Northwest Passage for longer periods of the year due to the loss of Arctic sea ice. However, in the long run, if a "business as usual" approach to emitting heat-trapping gases is maintained at the present rate, or faster, then the negative costs and impacts of global warming are very likely to far outweigh the benefits over the course of this century, with increased potential for catastrophic impacts from more extreme events. [ 17 ] In part, this is because any substantial change, whether warmer or colder, would challenge the societal infrastructure that has developed under the current climate.

IPCC (2012): Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation . A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, UK, and New York, NY, USA, 582 pp.

USGCRP (2017). Climate Science Special Report: Fourth National Climate Assessment, Volume 1 [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp, doi: 10.7930/J0J964J6 .

Hoegh-Guldberg, O., D. Jacob, M. Taylor, M. Bindi, S. Brown, I. Camilloni, A. Diedhiou, R. Djalante, K.L. Ebi, F. Engelbrecht, J.Guiot, Y. Hijioka, S. Mehrotra, A. Payne, S.I. Seneviratne, A. Thomas, R. Warren, and G. Zhou. (2018). Impacts of 1.5°C Global Warming on Natural and Human Systems. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W.

We value your feedback

Help us improve our content

Renewable energy, explained

Solar, wind, hydroelectric, biomass, and geothermal power can provide energy without the planet-warming effects of fossil fuels.

In any discussion about climate change , renewable energy usually tops the list of changes the world can implement to stave off the worst effects of rising temperatures. That's because renewable energy sources such as solar and wind don't emit carbon dioxide and other greenhouse gases that contribute to global warming .

Clean energy has far more to recommend it than just being "green." The growing sector creates jobs , makes electric grids more resilient, expands energy access in developing countries, and helps lower energy bills. All of those factors have contributed to a renewable energy renaissance in recent years, with wind and solar setting new records for electricity generation .

For the past 150 years or so, humans have relied heavily on coal, oil, and other fossil fuels to power everything from light bulbs to cars to factories. Fossil fuels are embedded in nearly everything we do, and as a result, the greenhouse gases released from the burning of those fuels have reached historically high levels .

As greenhouse gases trap heat in the atmosphere that would otherwise escape into space, average temperatures on the surface are rising . Global warming is one symptom of climate change, the term scientists now prefer to describe the complex shifts affecting our planet’s weather and climate systems. Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and habitats, rising seas , and a range of other impacts .

Of course, renewables—like any source of energy—have their own trade-offs and associated debates. One of them centers on the definition of renewable energy. Strictly speaking, renewable energy is just what you might think: perpetually available, or as the U.S. Energy Information Administration puts it, " virtually inexhaustible ." But "renewable" doesn't necessarily mean sustainable, as opponents of corn-based ethanol or large hydropower dams often argue. It also doesn't encompass other low- or zero-emissions resources that have their own advocates, including energy efficiency and nuclear power.

Types of renewable energy sources

Hydropower: For centuries, people have harnessed the energy of river currents, using dams to control water flow. Hydropower is the world's biggest source of renewable energy by far, with China, Brazil, Canada, the U.S., and Russia the leading hydropower producers . While hydropower is theoretically a clean energy source replenished by rain and snow, it also has several drawbacks.

For Hungry Minds

Large dams can disrupt river ecosystems and surrounding communities , harming wildlife and displacing residents. Hydropower generation is vulnerable to silt buildup, which can compromise capacity and harm equipment. Drought can also cause problems. In the western U.S., carbon dioxide emissions over a 15-year period were 100 megatons higher than they normally would have been, according to a 2018 study , as utilities turned to coal and gas to replace hydropower lost to drought. Even hydropower at full capacity bears its own emissions problems, as decaying organic material in reservoirs releases methane.

Dams aren't the only way to use water for power: Tidal and wave energy projects around the world aim to capture the ocean's natural rhythms. Marine energy projects currently generate an estimated 500 megawatts of power —less than one percent of all renewables—but the potential is far greater. Programs like Scotland’s Saltire Prize have encouraged innovation in this area.

Wind: Harnessing the wind as a source of energy started more than 7,000 years ago . Now, electricity-generating wind turbines are proliferating around the globe, and China, the U.S., and Germany are the leading wind energy producers. From 2001 to 2017 , cumulative wind capacity around the world increased to more than 539,000 megawatts from 23,900 mw—more than 22 fold.

Some people may object to how wind turbines look on the horizon and to how they sound, but wind energy, whose prices are declining , is proving too valuable a resource to deny. While most wind power comes from onshore turbines, offshore projects are appearing too, with the most in the U.K. and Germany. The first U.S. offshore wind farm opened in 2016 in Rhode Island, and other offshore projects are gaining momentum . Another problem with wind turbines is that they’re a danger for birds and bats, killing hundreds of thousands annually , not as many as from glass collisions and other threats like habitat loss and invasive species, but enough that engineers are working on solutions to make them safer for flying wildlife.

Can energy harnessed from Earth’s interior help power the world?

How the historic climate bill will dramatically reduce U.S. emissions

5 environmental victories from 2021 that offer hope

Solar: From home rooftops to utility-scale farms, solar power is reshaping energy markets around the world. In the decade from 2007 and 2017 the world's total installed energy capacity from photovoltaic panels increased a whopping 4,300 percent .

In addition to solar panels, which convert the sun's light to electricity, concentrating solar power (CSP) plants use mirrors to concentrate the sun's heat, deriving thermal energy instead. China, Japan, and the U.S. are leading the solar transformation, but solar still has a long way to go, accounting for around two percent of the total electricity generated in the U.S. in 2017. Solar thermal energy is also being used worldwide for hot water, heating, and cooling.

Biomass: Biomass energy includes biofuels such as ethanol and biodiesel , wood and wood waste, biogas from landfills, and municipal solid waste. Like solar power, biomass is a flexible energy source, able to fuel vehicles, heat buildings, and produce electricity. But biomass can raise thorny issues.

Critics of corn-based ethanol , for example, say it competes with the food market for corn and supports the same harmful agricultural practices that have led to toxic algae blooms and other environmental hazards. Similarly, debates have erupted over whether it's a good idea to ship wood pellets from U.S. forests over to Europe so that it can be burned for electricity. Meanwhile, scientists and companies are working on ways to more efficiently convert corn stover , wastewater sludge , and other biomass sources into energy, aiming to extract value from material that would otherwise go to waste.

Geothermal: Used for thousands of years in some countries for cooking and heating, geothermal energy is derived from the Earth’s internal heat . On a large scale, underground reservoirs of steam and hot water can be tapped through wells that can go a mile deep or more to generate electricity. On a smaller scale, some buildings have geothermal heat pumps that use temperature differences several feet below ground for heating and cooling. Unlike solar and wind energy, geothermal energy is always available, but it has side effects that need to be managed, such as the rotten egg smell that can accompany released hydrogen sulfide.

Ways to boost renewable energy

Cities, states, and federal governments around the world are instituting policies aimed at increasing renewable energy. At least 29 U.S. states have set renewable portfolio standards —policies that mandate a certain percentage of energy from renewable sources, More than 100 cities worldwide now boast at least 70 percent renewable energy, and still others are making commitments to reach 100 percent . Other policies that could encourage renewable energy growth include carbon pricing, fuel economy standards, and building efficiency standards. Corporations are making a difference too, purchasing record amounts of renewable power in 2018.

Wonder whether your state could ever be powered by 100 percent renewables? No matter where you live, scientist Mark Jacobson believes it's possible. That vision is laid out here , and while his analysis is not without critics , it punctuates a reality with which the world must now reckon. Even without climate change, fossil fuels are a finite resource, and if we want our lease on the planet to be renewed, our energy will have to be renewable.

Activists fear a new threat to biodiversity—renewable energy

How the Ukraine war is accelerating Germany's renewable energy transition

We took the Great American Road Trip—in electric cars

What’s at stake at COP26—the crucial global climate summit

3 ways COVID-19 is making us rethink energy and emissions

Environment
Perpetual Planet

History & Culture

History & Culture
History Magazine
Mind, Body, Wonder
Paid Content
Terms of Use
Privacy Policy
Your US State Privacy Rights
Children's Online Privacy Policy
Interest-Based Ads
About Nielsen Measurement
Do Not Sell or Share My Personal Information
Nat Geo Home
Attend a Live Event
Book a Trip
Inspire Your Kids
Shop Nat Geo
Visit the D.C. Museum
Learn About Our Impact
Support Our Mission
Advertise With Us
Customer Service
Renew Subscription
Manage Your Subscription
Work at Nat Geo
Sign Up for Our Newsletters
Contribute to Protect the Planet

Knowledge is power

Stay in the know about climate impacts and solutions. Subscribe to our weekly newsletter.

By clicking submit, you agree to share your email address with the site owner and Mailchimp to receive emails from the site owner. Use the unsubscribe link in those emails to opt out at any time.

Yale Climate Connections

The pros and cons of planting trees to address global warming

Cautions against just randomly digging and planting

Over the past few weeks, chatter has picked up that planting trees is only one piece of the puzzle when it comes to combating climate change. Trees are a good thing, but:

We also need to protect existing forests – the Amazon, for example.
We need to ramp up wind, solar, and geothermal energy.
We need to burn less fossil fuel.
We need to eat more of the right foods and less of the wrong ones and, above all else, eat sustainably.
We need higher vehicle-mileage standards and more electric cars.
We need to get our act together so we can better adapt to rising seas, more droughts and wildfires, and unpredictable swings in weather.

Like other initiatives to tackle climate change, planting trees requires some forethought. Recent news coverage of the trillion tree campaign points to several things people should be thinking about before digging and planting.

Authors of a 2019 study from the Swiss research university, ETH Zurich, estimated that the planet can support about 2.5 billion more acres of newly planted trees – without tearing down cities and doing away with farms. And they say those trees could store about 200 gigatons of carbon (GtC) once they mature. That’s equal to one-third of all the carbon that humans have emitted into the atmosphere as carbon dioxide pollution, the authors claimed. The New York Times summarized the study last year.

Researcher: ‘Nations absolutely should plant and protect as many [trees] as possible. … But it’s also a limited and unreliable way of addressing climate change.’

Scientist Zeke Hausfather, long a regular contributor to Yale Climate Connections, suggested in a series of tweets at the time that the study was misleading on a few counts. For one thing, cumulative emissions from land use and burning fossil fuels were closer to 640 GtC, “so removing 200 GtC would represent one-third of historic emissions.” Hausfather also pointed to the practical and economic challenges of planting trees on every acre of available land.

India is intimately familiar with this challenge. Last summer the country planted hundreds of millions of trees as part of an initiative to keep one-third of its land area covered in trees. But the nation’s high population and rapid industrialization pose challenges to sustained reforestation. Only about 60% of the saplings are expected to survive – the rest succumbing to disease and a lack of water.

A Skeptical Science article by Dana Nuccitelli, a regular contributor to Yale Climate Connections and an environmental scientist, cites additional studies that have raised several other key points. Among them:

Tundra and boreal regions unpopulated by trees play an important global role in reflecting energy from the sun back into space. Planting trees in these regions would darken landscapes at these high latitudes, causing them to absorb energy from the sun rather than reflect it – ultimately contributing to higher global temperatures and offsetting cooling created by planting trees.
The ETH Zurich researchers mistakenly considered natural savannas, grasslands, and shrublands as places where forests could be restored.
And in their ETH Zurich study, they estimated a carbon sequestration rate of 0.22 GtC per million hectares (i.e., for every 2.47 million acres). But 0.22 GtC is twice the amount cited by previously published estimates.

Trees deserve a ‘moment’ of fame, but keep reality in mind

So while the right kinds and numbers of tree species in the right places have lots of appeal, big questions remain over exactly what can be accomplished by planting one trillion trees – and whether it may cause more harm than good.

James Temple, senior editor for energy at MIT Technology Review, summed up the view of many experts in a January 28 piece when he wrote:

“It’s great that trees are having a moment. Nations absolutely should plant and protect as many as possible. … But it’s also a limited and unreliable way of addressing climate change.”

Temple raised a few more important points, some of which have been echoed elsewhere. Among them: trees take time to grow and reach maturity – decades and even centuries for redwoods and other behemoths that can store massive amounts of carbon. If you think you’re going to immediately offset your carbon footprint from flying across the country by planting a tree … think again.

Another point Temple made: You really have to work the numbers to get a true sense of the challenge. For example, he wrote, the U.S. produced 5.8 billion gigatons of carbon dioxide emissions in 2019. To offset that much CO2 pollution, you’d have to plant a forest – and wait for it to fully mature – that is more than twice the size of Texas.

The one-trillion tree campaign raises still more questions for forest ecologists – one of them having to do with biodiversity. If the campaign results in what are essentially tree plantations lacking biodiversity and genetic variation, often referred to as monoculture, those artificial forests won’t get very far.

“People are getting caught up in the wrong solution,” Forrest Fleischman of the University of Minnesota told The Verge in late January . “Instead of that guy from Salesforce saying, ‘I’m going to put money into planting a trillion trees,’ I’d like him to go and say, ‘I’m going to put my money into helping indigenous people in the Amazon defend their lands.’ That’s going to have a bigger impact.”

A campaign to plant “one trillion trees” sounds ambitious, it sounds daring, and it sounds exciting. And in many ways it could be all of those. But keep in mind that since 2015 and just in the Sierra Nevada – that sliver of mountain habitat that runs along the spine of California – nearly 150 million trees have died , victims of drought, disease, and invasion by beetles. Warmer winters have contributed to a population explosion of these destructive insects, and it’s a story being played out across the American West where forest fires are growing in frequency and intensity.

So maybe we can plant a trillion trees around the globe. But if we don’t do much else about climate change, will we just be fueling the fire?

So maybe we can and should plant a trillion trees around the globe. Go for it. But a wide array of experts insist that if we don’t also take numerous other actions to address climate change – specifically including major cuts in fossil fuel emissions and in particular carbon dioxide – we may just be fueling the fire.

In the end, it comes down to more trees and lots of other actions, not to more trees or .

Bruce Lieberman

Bruce Lieberman, a long-time journalist, has covered climate change science, policy, and politics for nearly two decades. A newspaper reporter for 20 years, Bruce worked for The San Diego Union-Tribune... More by Bruce Lieberman

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Publications
Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

Advanced Search
Journal List
Front Plant Sci

Climate Change and the Impact of Greenhouse Gasses: CO 2 and NO, Friends and Foes of Plant Oxidative Stress

Here, we review information on how plants face redox imbalance caused by climate change, and focus on the role of nitric oxide (NO) in this response. Life on Earth is possible thanks to greenhouse effect. Without it, temperature on Earth’s surface would be around -19°C, instead of the current average of 14°C. Greenhouse effect is produced by greenhouse gasses (GHG) like water vapor, carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxides (N x O) and ozone (O 3 ). GHG have natural and anthropogenic origin. However, increasing GHG provokes extreme climate changes such as floods, droughts and heat, which induce reactive oxygen species (ROS) and oxidative stress in plants. The main sources of ROS in stress conditions are: augmented photorespiration, NADPH oxidase (NOX) activity, β-oxidation of fatty acids and disorders in the electron transport chains of mitochondria and chloroplasts. Plants have developed an antioxidant machinery that includes the activity of ROS detoxifying enzymes [e.g., superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX), and peroxiredoxin (PRX)], as well as antioxidant molecules such as ascorbic acid (ASC) and glutathione (GSH) that are present in almost all subcellular compartments. CO 2 and NO help to maintain the redox equilibrium. Higher CO 2 concentrations increase the photosynthesis through the CO 2 -unsaturated Rubisco activity. But Rubisco photorespiration and NOX activities could also augment ROS production. NO regulate the ROS concentration preserving balance among ROS, GSH, GSNO, and ASC. When ROS are in huge concentration, NO induces transcription and activity of SOD, APX, and CAT. However, when ROS are necessary (e.g., for pathogen resistance), NO may inhibit APX, CAT, and NOX activity by the S-nitrosylation of cysteine residues, favoring cell death. NO also regulates GSH concentration in several ways. NO may react with GSH to form GSNO, the NO cell reservoir and main source of S-nitrosylation. GSNO could be decomposed by the GSNO reductase (GSNOR) to GSSG which, in turn, is reduced to GSH by glutathione reductase (GR). GSNOR may be also inhibited by S-nitrosylation and GR activated by NO. In conclusion, NO plays a central role in the tolerance of plants to climate change.

Introduction

Life on Earth, as it is, relies on the natural atmospheric greenhouse effect. This is the result of a process in which a planet’s atmosphere traps the sun radiation and warms the planet’s surface.

Greenhouse effect occurs in the troposphere (the lower atmosphere layer), where life and weather occur. In the absence of greenhouse effect, the average temperature on Earth’s surface is estimated around -19°C, instead of the current average of 14°C ( Le Treut et al., 2007 ). Greenhouse effect is produced by greenhouse gasses (GHG). GHG are those gaseous constituents of the atmosphere that absorb and emit radiation in the thermal infrared range ( IPCC, 2014 ). Traces of GHG, both natural and anthropogenic, are present in the troposphere. The most abundant GHG in increasing order of importance are: water vapor, carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxides (N x O) and ozone (O 3 ) ( Kiehl and Trenberth, 1997 ). GHG percentages vary daily, seasonally, and annually.

GHG Contribute Differentially to Greenhouse Effect

Water vapor.

Water is present in the troposphere both as vapor and clouds. Water vapor was reported by Tyndal in 1861 as the most important gaseous absorber of variations in infrared radiation (cited in Held and Souden, 2000 ). Further accurate calculation estimate that water vapor and clouds are responsible for 49 and 25%, respectively, of the long wave (thermal) absorption ( Schmidt et al., 2010 ). However, atmospheric lifetime of water vapor is short (days) compared to other GHG as CO 2 (years) ( IPCC, 2014 ).

Water vapor concentrations are not directly influenced by anthropogenic activity and vary regionally. However, human activity increases global temperatures and water vapor formation indirectly, amplifying the warming in a process known as water vapor feedback ( Soden et al., 2005 ).

Carbon Dioxide (CO 2 )

Carbon dioxide is responsible for 20% of the thermal absorption ( Schmidt et al., 2010 ).

Natural sources of CO 2 include organic decomposition, ocean release and respiration. Anthropogenic CO 2 sources are derived from activities such as cement manufacturing, deforestation, fossil fuels combustion such as coal, oil and natural gas, etc. Surprisingly, 24% of direct CO 2 emission comes from agriculture, forestry and other land use, and 21% comes from industry ( IPCC, 2014 ).

Atmospheric CO 2 concentrations climbed up dramatically in the past two centuries, rising from around 270 μmol.mol -1 in 1750 to present concentrations higher than 385 μmol.mol -1 ( Mittler and Blumwald, 2010 ; IPCC, 2014 ). Around 50% of cumulative anthropogenic CO 2 emissions between 1750 and 2010 have taken place since the 1970s ( IPCC, 2014 ). It is calculated that the temperature rise produced by high CO 2 concentrations, plus the water positive feedback, would increase by 3–5°C the global mean surface temperature in 2100 ( IPCC, 2014 ).

Methane (CH 4 )

Methane (CH 4 ) is the main atmospheric organic trace gas. CH 4 is the primary component of natural gas, a worldwide fuel source. Significant emissions of CH 4 result from cattle farming and agriculture, but mainly as a consequence of fossil fuel use. Concentrations of CH 4 were multiplied by two since the pre-industrial era. The present worldwide-averaged concentration is of 1.8 μmol.mol -1 ( IPCC, 2014 ).

Although its concentration represents only 0.5% that of CO 2 , concerns arise regarding a jump in CH 4 atmospheric release. Indeed, it is 30 times more powerful than CO 2 as GHG ( IPCC, 2014 ). CH 4 generates O 3 (see below), and along with carbon monoxide (CO), contributes to control the amount of OH in the troposphere ( Wuebbles and Hayhoe, 2002 ).

Nitrous Oxides (NxO)

Nitrous oxide (N 2 O) and nitric oxide (NO) are GHG. During the last century, their global emissions have rised, due mainly to human intervention ( IPCC, 2014 ). The soil emits both N 2 O and NO. N 2 O is a strong GHG, whereas NO contributes indirectly to O 3 synthesis. As GHG, N 2 O is potentially 300 times stronger than CO 2 . Once in the stratosphere, the former catalyzes the elimination of O 3 ( IPCC, 2014 ). In the atmosphere, N 2 O concentrations are climbing up due mainly to microbial activity in nitrogen (N)-rich soils related with agricultural and fertilization practices ( Hall et al., 2008 ).

Anthropogenic emissions (from combustion of fossil fuels) and biogenic emissions from soils are the main sources of NO in the atmosphere ( Medinets et al., 2015 ). In the troposphere, NO quickly oxidizes to nitrogen dioxide (NO 2 ). NO and NO 2 (termed as NO x ) may react with volatile organic compounds (VOCs) and hydroxyl, resulting in organic nitrates and nitric acid, respectively. They access ecosystems through atmospheric deposition that has an impact on the N cycle as a result of acidification or N enrichment ( Pilegaard, 2013 ).

NO Sources and Chemical Reactions in Plants

Two major pathways for NO production have been described in plants: the reductive and the oxidative pathways. The reductive pathway involves the reduction of nitrite to NO by NR under conditions such as acidic pH, anoxia, or an increase in nitrite levels ( Rockel et al., 2002 ; Meyer et al., 2005 ). NR-dependent NO formation has been involved in processes such as stomatal closure, root development, germination and immune responses. In plants, nitrite may also be reduced enzymatically by other molybdenum enzymes such as, xanthine oxidase, aldehyde oxidase, and sulfite oxidase, in animals ( Chamizo-Ampudia et al., 2016 ) or via the electron transport system in mitochondria ( Gupta and Igamberdiev, 2016 ).

The oxidative pathway produces NO through the oxidation of organic compounds such as polyamines, hydroxylamine and arginine. In animals, NOS catalyzes arginine oxidation to citrulline and NO. Many efforts were made to find the arginine-dependent NO formation in plants, as well as of plant NOS ( Frohlich and Durner, 2011 ). The identification of NOS in the green alga Ostreococcus tauri ( Foresi et al., 2010 ) led to high-throughput bioinformatic analysis in plant genomes. This study shows that NOS homologs were not present in over 1,000 genomes of higher plants analyzed, but only in few photosynthetic microorganisms, such as algae and diatoms ( Di Dato et al., 2015 ; Kumar et al., 2015 ; Jeandroz et al., 2016 ). In summary, although an arginine-dependent NO production is found in higher plants, the specific enzyme/s involved in the oxidative pathways remain elusive.

Ozone (O 3 )

Ozone (O 3 ) is mainly found in the stratosphere, but a little amount is generated in the troposphere. Stratospheric ozone (namely the ozone layer) is formed naturally by chemical reactions involving solar ultraviolet (UV) radiation and O 2 . Solar UV radiation breaks one O 2 molecule, producing two oxygen atoms (2 O). Then, each of these highly reactive atoms combines with O 2 to produce an (O 3 ) molecule. Almost 99% of the Sun’s medium-frequency UV light (from about 200 to 315 nm wavelength) is absorbed by the (O 3 ) layer. Otherwise, they could damage exposed life forms near the Earth surface 1 .

The majority of tropospheric O 3 appears when NOx, CO and VOCs, react in the presence of sunlight. However, it was reported that NOx may scavenge O 3 in urban areas ( Gregg et al., 2003 ). This dual interaction between NOx and O 3 is influenced by light, season, temperature and VOC concentration ( Jhun et al., 2015 ).

Besides, the oxidation of CH 4 by OH in the troposphere gives way to formaldehyde (CH 2 O), CO, and O 3 , in the presence of high amounts of NOx 1 .

Tropospheric O 3 is harmful to both plants and animals (including humans). O 3 affects plants in several ways. Stomata are the cells, mostly on the underside of the plant leaves, that allow CO 2 and water to diffuse into the tissue. High concentrations of O 3 cause plants to close their stomata ( McAdam et al., 2017 ), slowing down photosynthesis and plant growth. O 3 may also provoke strong oxidative stress, damaging plant cells ( Vainonen and Kangasjärvi, 2015 ).

Global Climate Change: an Integrative Balance of the Impact on Plants

Anthropogenic activity alters global climate by interfering with the flows of energy through changes in atmospheric gasses composition, more than the actual generation of heat due to energy usage ( Karl and Trenberth, 2003 ). Short-term consequences of GHG increase in plants are mainly associated with the rise in atmospheric CO 2 . Plants respond directly to elevated CO 2 increasing net photosynthesis, and decreasing stomatal opening ( Long et al., 2004 ). To a lesser extent, O 3 uptake by plants may reduce photosynthesis and induce oxidative stress. In the middle and long term, prognostic consensus about climate change signal a rise in CO 2 concentration and temperature on the Earth’s surface, unexpected variations in rainfall, and more recurrent and intense weather conditions, e.g., heat waves, drought and flooding events ( Mittler and Blumwald, 2010 ; IPCC, 2014 ). These brief episodes bring plants beyond their capacity of adaptation; decreasing crop and tree yield ( Ciais et al., 2005 ; Zinta et al., 2014 ).

Here we will not discuss plants capacity of adaptation to novel environmental conditions when considering large scales and long-term periods. Ecosystems are being affected by climate change at all levels (terrestrial, freshwater, and marine), and it was already reported that species are under evolutionary adaptation to human-caused climate change (for a review see Scheffers et al., 2016 ). Migration and plasticity are two biological mechanisms to cope with these changes. Data indicate that each population of a species has limited tolerance to sharp climate variations, and they could migrate to find more favorable environments. Habitat fragmentation limits plant movement, being other big threat for adaptation ( Stockwell et al., 2003 ; Leimu et al., 2010 ). Despite the fact that individual plants are immobile, plant populations move when seeds are dispersed, resulting in differences in the general distribution of the species ( Corlett and Westcott, 2013 ). In this sense, anthropogenic activities also contribute to seed dispersal.

Plasticity is a characteristic related to phenology and phenotype. Phenology is the timing of phases occurrence in the life cycle, and phenotypic plasticity is the range of phenotypes that a single genotype may express depending on its environment ( Nicotra et al., 2010 ). Plasticity is adaptive when the phenotype changes occur in a direction favored by selection in the new environment.

Climate Change and ROS

Reactive Oxygen Species (ROS) are continuously generated by plants under normal conditions. However, they are increased in response to different abiotic stresses. One of the most important effects of climate change-related stresses at the molecular level is the increase of ROS inside the cells ( Farnese et al., 2016 ). Among ROS, the most studied are superoxide anion ( O 2 •– ), H 2 O 2 and the hydroxyl radical (⋅OH - ).

Reactive Oxygen Species cause damage to proteins, lipids and DNA, affecting cell integrity, morphology, physiology, and, consequently, the growth of plants ( Frohnmeyer and Staiger, 2003 ). The main sources of ROS in stress conditions are: augmented photorespiration, NADPH oxidase (NOX) activity, β-oxidation of fatty acids and disorders in the electron transport chains of mitochondrias and chloroplasts ( Apel and Hirt, 2004 ; AbdElgawad et al., 2015 ). Hence, higher plants have evolved in the presence of ROS and have acquired pathways to protect themselves from its toxicity. Plant antioxidant system (AS) includes the activity of ROS detoxifying enzymes [e.g., superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione peroxidase (GPX), and peroxiredoxin (PRX)], as well as antioxidant molecules such as ascorbic acid (ASC) and glutathione (GSH) that are present in almost all subcellular compartments (reviewed by Choudhury et al., 2017 ).

In this context, plants have also developed a tight interaction between ROS and NO as a mechanism to reduce the deleterious consequences of these ROS-induced oxidative injuries. NO orchestrates a wide range of mechanisms leading to the preservation of redox homeostasis in plants. Consequently, NO at low concentration is considered a broad-spectrum anti-stress molecule ( Lamattina et al., 2003 ; Tossi et al., 2009 ; Correa-Aragunde et al., 2015 ). Figure Figure1 1 shows the relationship among the different GHG and their impact on plants.

An external file that holds a picture, illustration, etc.
Object name is fpls-09-00273-g001.jpg

Simplified scheme showing greenhouse gasses (GHG) and their effects on plants. GHG (H 2 O vapor, clouds, CO 2 , CH 4 , N 2 O, and NO) have both natural and anthropogenic origin, contributing to greenhouse effect. Short-term effects of GHG increase is mainly CO 2 rise, that activates photosynthesis (PS) and inhibits stomatal opening (SO). Long-term effects of GHG increase are extreme climate changes such as floods, droughts, heat. All of them induce the generation of reactive oxygen species (ROS) and oxidative stress in plants. Nitric oxide (NO) could alleviate oxidative stress by scavenging ROS and/or regulating the antioxidant system (AS). GHG and volatile organic compounds (VOC) react in presence of sunlight (E#) to give tropospheric O 3 . Although tropospheric O 3 is prejudicial for life, stratospheric O 3 is beneficial, because filters harmful UV-B radiation. The size of arrows are representative of the GHG concentration.

CO 2 and NO Contribute to Regulate Redox Homeostasis in Plants

Co 2 increasing: advantages and disadvantages.

Increased CO 2 was suggested to have a “fertilization” effect, because crops would increase their photosynthesis and stomatal conductance in response to elevated CO 2 . This belief was supported by studies performed in greenhouses, laboratory controlled-environment chambers, and transparent field chambers, where emitted CO 2 may be held back and readily controlled ( Drake et al., 1997 ; Markelz et al., 2014 ). However, more realistic results, obtained by Free-Air Concentration Enrichment (FACE) technology, suggest that the fertilization response due to CO 2 increase is probably dependent on genetic and environmental factors, and the duration of the study ( Smith and Dukes, 2013 ). An extensive review of the literature in this field made by Xu et al. (2015) concluded that augmented CO 2 normally increases photosynthesis in C3 species such as rice, soybean and wheat. On the other hand, they pointed out that a negative feedback of photosynthesis could take place in augmented CO 2 , as a result of overload of chemical and reactive generated substrates, leading to an imbalance in the sink:source carbon ratio. Moreover, the energetic cost of carbohydrate exportation increases in elevated CO 2 level.

The most important photosynthetic enzyme is the ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO). Rubisco is located in mesophyll cells of C3 plants, in direct contact with the intercellular air space linked to the atmosphere by epidermal stomatal pores. Photosynthesis increases at high CO 2 , because Rubisco is not CO 2 saturated and CO 2 inhibits the oxygenation reactions and photorespiration ( Long et al., 2006 ). However, long-term high concentration of CO 2 may down regulate Rubisco activity because ribulose-1,5-bisphosphate is not regenerated. Hexokinase (HXK), a sensor of extreme photosynthate, may participate in the down regulation of Rubisco concentration ( Xu et al., 2015 ). Moreover, severe abiotic stresses, such as temperature and drought, may restrain Rubisco carboxylation and foster oxygenation ( Xu et al., 2015 ).

In C4 crops, such as maize and sorghum, the elevated concentration of CO 2 inside the bundle sheath cells could prevent a large increase of Rubisco activity at higher atmospheric CO 2 and, thereby, photosynthetic activity is not augmented. However, at high CO 2 levels, the water status of C4 plants under drought conditions is improved, increasing photosynthesis and biomass accumulation ( Long et al., 2006 ; Mittler and Blumwald, 2010 ). That envisages potential advantages for the C4 species in future climatic change scenarios, particularly in arid and semiarid areas.

In addition, high CO 2 has the benefit of reducing stomatal conductance, decreasing 10% evapotranspiration in both C3 and C4 plants. Simultaneously, the cooling decreased resulting from reduced transpiration causes elevated canopy temperatures of around 0.7°C for most crops. Biomass and yield rise due to high CO 2 in all C3 plants, but not in C4 plants exception made when water is a restraint. Yields of C3 grain crops jump around 19% on average at high CO 2 ( Kimball, 2016 ).

Some reports analyze the contribution of CO 2 in the responses of plants to the combination of multiple stresses. For Arabidopsis thaliana , the combination of heat and drought induces photosynthesis inhibition of 62% under ambient CO 2 , but the drop in photosynthesis is just 40% at high CO 2 . Moreover, the protein oxidation increases significantly during a heat wave and drought, and this effect is repressed by increased CO 2 . Photorespiration is also reduced by high CO 2 ( Zinta et al., 2014 ).

Studying grasses ( Lolium perenne, Poa pratensis ) and legumes ( Medicago lupulina, Lotus corniculatus ) exposed to drought, high temperature and augmented CO 2 , AbdElgawad et al. (2015) demonstrated that drought suppresses plant growth, photosynthesis and stomatal conductance, and promotes in all species the synthesis of osmolytes and antioxidants. Instead, oxidative damage is more markedly observed in legumes than in grasses. In general, warming amplifies drought consequences. In contrast, augmented CO 2 diminishes stress impact. Reduction in photosynthesis and chlorophyll, as a result of drought and elevated temperature, were avoided by high CO 2 in the grasses. Noxious effects of oxidative stress, i.e., lipid peroxidation, are phased down in all species by augmented CO 2 . Normally, a reduced impact of oxidative stress is due to decreased photorespiration and diminished NOX activity. In legumes, a rise in levels of antioxidant molecules (flavonoids and tocopherols) contribute as well to the stress mitigation caused by augmented CO 2 . The authors draw the conclusion that these different responses point at an unequal future impact of climate change on the production of agricultural-scale legumes and grass crops.

Kumari et al. (2015) assessed the impact of various levels of CO 2 , ambient (382 ppm) and augmented (570 ppm), and O 3 , ambient (50 ppb) and augmented (70 ppb) on the potato physiological and biochemical responses ( Solanum tuberosum ). They observed that augmented CO 2 cut down O 3 uptake, enhanced carbon assimilation, and curbed oxidative stress. Elevated CO 2 also mitigated the noxious effect of high O 3 on photosynthesis.

Although some molecular mechanisms underpinning CO 2 actions are unknown, the results presented highlight the importance of CO 2 as a regulator that mitigates the potential climate change-induced deleterious consequences in plants. Recent reports suggest that some CO 2 -associated responses may be mediated by NO.

Du et al. (2016) determined that 800 μmol.mol -1 of CO 2 increased the NO concentration in Arabidopsis leaves, through a mechanism related to nitrate availability. Moreover, NO increase, as a consequence of high CO 2 levels, was reported as a general procedure to improve iron (Fe) nutrition in response to Fe deficiency in tomato roots ( Jin et al., 2009 ).

The gas exchange between the atmosphere and plants is mainly regulated by stomata. But structure and physiology of stomata are also influenced by gasses ( García-Mata and Lamattina, 2013 ). Elevated CO 2 regulate stomatal density and conductance. Moreover, there is increasing evidence that this response is modified by interaction of CO 2 with other environmental factors ( Xu et al., 2016 ; Yan et al., 2017 ). Wang et al. (2015) reported that 800 μmol.mol -1 of CO 2 increases the NO concentration in A. thaliana guard cells, inducing stomatal closure. Both NR and NO synthase (NOS)-like activities are necessary for CO 2 -induced NO accumulation. Comprehensive pharmacological and genetic results obtained in Arabidopsis by Chater et al. (2015) , show that when CO 2 concentration is around 700–1000 ppm, stomatal density and closure are reduced. They also illustrate that those elements necessary for this process are: activation of both ABA biosynthesis genes and the PYR/RCAR ABA receptor, and ROS increase. However, Shi et al. (2015) provide genetic and pharmacological evidence that high CO 2 concentration induces stomatal closure by an ABA-independent mechanism in tomato. They show that 800 μmol.mol -1 of CO 2 increase the expression of the protein kinase OPEN STOMATA 1 (OST1), NOX, and nitrate reductase (NR) genes. They also show that the sequential production of NOX-dependent H 2 O 2 and NR-produced NO are mainly dependent of OST1, and are involved in the CO 2 -induced stomatal closure.

In ABA-dependent mechanisms, ABA is increased by CO 2. The binding of ABA to its receptor (PYR/RCAR) inactivates PP2C, activating OST1. In ABA-independent mechanism, OST1 will be transcriptionally induced by CO 2 . Once activated, OST1 along with Ca 2 + , activates NOX, increasing ROS ( Kim et al., 2010 ). The rise of guard cells ROS enhances NO, cytosolic free Ca 2 + , and pH ( Song et al., 2014 ; Xie et al., 2014 ). ROS and NO release Ca 2 + from internal reservoirs, or influx external Ca 2 + through plasma membrane Ca 2 + in channels. Cytosolic free Ca 2 + inactivate inward K + channels (K + in ) to prevent K + uptake and activate outward K + channels (K + out ) and Cl - (anion) channels (Cl - ) at the plasma membrane ( Blatt, 2000 ; García-Mata et al., 2003 ). Ca 2 + also activates slow anion channel homolog 3 (SLAH3), slow anion channel-associated 1 (SLAC1) and aluminum activated malate transporters (ALMT) ( Roelfsema et al., 2012 ). The consequence of the regulation of cation/anion channels is the net efflux of K + /Cl - /malate and influx of Ca 2 + , making guard cells lose turgor by water outlet, causing stomatal closure.

All together, the results discussed here suggest that CO 2 -induced NO increase is a common plant physiological response to oxidative stresses. Figure Figure2 2 shows the importance of CO 2 and NO in these processes.

An external file that holds a picture, illustration, etc.
Object name is fpls-09-00273-g002.jpg

Interplay between CO 2 and NO in plant redox physiology: CO 2 enters to the leaves by stomata. Once in mesophyll cells, CO 2 increase photosynthesis (PS) through the CO 2 -unsaturated Rubisco activity. When plants are in stress environments, ROS could be augmented by Rubisco-induced photorespiration and NADPH oxidase (NOX) activities. NOX- induced O 2 •– , in the apoplast is immediately transformed to H 2 O 2 by the superoxide dismutase (SOD). Plasma membrane is permeable to H 2 O 2 . CO 2 moderates oxidative stress in mesophyll cells by inhibiting both Rubisco photorespiration (PR) and NOX activities. Besides, NO is induced by CO 2 and ROS, alleviating the consequences of oxidative stress by scavenging ROS and activating or inhibiting the antioxidant system (AS). In guard cells, CO 2 increases the expression and activity of OPEN STOMATA 1 (OST1), in both ABA-dependent and independent mechanisms. OST1 activates NOX, producing ROS and consequently NO increase by nitrate reductase (NR), and NOS-like activities. NO prevents ROS increase by direct scavenging, and inhibiting NOX. NO-dependent Ca 2 + regulated ion channels induces stomatal closure, modulating O 3 and CO 2 uptake, decreasing evapotranspiration, and rising leaf temperature.

Abiotic Stress, ROS Generation, and Redox Balance: The Key Role of NO

Reactive oxygen species are generated in apoplast, plasma membrane, chloroplasts, mitochondria, and peroxisomes ( Farnese et al., 2016 ). It was proposed that each stress produces its own “ROS signature” ( Choudhury et al., 2017 ). For instance, drought may reduce the activity of Rubisco, decreasing CO 2 fixation and NADP+ regeneration by the Calvin cycle. As a consequence, chloroplast electron transport is altered, generating ROS by electron leakage to O 2 ( Carvalho, 2008 ). In drought stress, ROS increase is produced by NOX activity ( Farnese et al., 2016 ). In flooding, ROS generation is an ethylene-promoted process that involves calcium (Ca 2+ ) flux, and NOX activity ( Voesenek and Bailey-Serres, 2015 ).

In heat stress, a NOX-dependent transient ROS rise is an early event ( Königshofer et al., 2008 ). Then, endogenous ROS are sensed through histidine kinases, and an Arabidopsis heat stress factor (HsfA4a) appears to sense exogenous ROS. As a result, the MAPK signal pathway is activated ( Qu et al., 2013 ). Moreover, functional decrease in photosynthetic light reaction induces ROS concentration by high electron leakage from the thylakoid membrane ( Hasanuzzaman et al., 2013 ). In this process, O 2 is the acceptor, generating O 2 •– .

Thus, individual stresses or their different combinations may produce particular “ROS signatures.” Besides their deleterious effects, ROS are recognized as a signal in the plant reaction to biotic and abiotic stressors. ROS may induce programed cell death (PCD) to avoid pathogen spread ( Mur et al., 2008 ), trigger a systemic defense response signal ( Dubiella et al., 2013 ), or avoid the chloroplast antenna overloading by electrons divert ( Choudhury et al., 2017 ).

Whatever the origin and function, ROS concentration must be adequately regulated to avoid excessive concentration and consequent cellular damages. Depending on NO and ROS concentrations, NO has the dual capacity to activate or inhibit the ROS production, and is a key molecule for keeping cellular redox homeostasis under control ( Beligni and Lamattina, 1999a ; Correa-Aragunde et al., 2015 ). NO has a direct ROS-scavenging activity because it holds an unpaired electron, reaching elevated reactivity with O 2 , O 2 •– , and redox active metals. NO can mitigate OH formation by scavenging either Fe or O 2 •– ( Lamattina et al., 2003 ). However, NO reacting with ROS (mainly O 2 •– ) may generate reactive nitrogen species (RNS). An excess of RNS originates a nitrosative stress ( Corpas et al., 2011 ). To avoid the toxicity of nitrosative stress, NO is stored as GSNO in the cell.

GSH as a Redox Buffer. GSNO as NO Reservoir. SNO and S-Nitrosylation

Glutathione (GSH) is a small peptide with the sequence γ-l-glutamyl-l-cysteinyl-glycine that has a cell redox homeostatic impact in most plant tissues. It is a soluble small thiol considered a non-enzymatic antioxidant. It exists in the reduced (GSH) or oxidized state (GSSG), in which two GSH molecules are joined by a disulfide bond ( Rouhier et al., 2008 ). GSH alleviates oxidative damages in plants generated by abiotic stresses, including salinity, drought, higher, low temperature, and heavy metals. GSH is precursor of phytochelatins, polymers that chelate toxic metals and transport them to the vacuole ( Grill et al., 1989 ). Studies shown that GSH contributes to tolerate nickel, cadmium, zinc, mercury, aluminum and arsenate heavy metals in plants ( Asgher et al., 2017 ). Moreover, GSH has a role in the detoxification of ROS both directly, interacting with them, or indirectly, participating of enzymatic pathways. GSH is involved in glutathionylation, a posttranslational modification that causes a mixed disulfide bond between a Cys residue and GSH.

GSH can be oxidized to GSSG by H 2 O 2 and can react with NO to form the nitrosoglutathione (GSNO) derivative. GSNO is an intracellular NO reservoir. It is also a vehicle of NO throughout the cell and organs, spreading NO biological function. GSNO is the largest low-molecular-mass S-nitrosothiol (SNO) in plant cells ( Corpas et al., 2013 ). GSNO metabolism and its reaction with other molecules involve S-nitrosylation and S-transnitrosation which consist of the binding of a NO molecule to a cysteine residue in proteins. Thioredoxin produces protein denitrosylation ( Correa-Aragunde et al., 2013 ). GSNO could be decomposed by the GSNO reductase (GSNOR) to GSSG which, in turn, is reduced to GSH by glutathione reductase (GR).

Glutathione also participates in the GSH/ASC cycle, a series of enzymatic reactions that degrade H 2 O 2 . APX degrades H 2 O 2 using ASC, the other major antioxidant in plants, as cofactor. The oxidized ASC is reduced by monodehydroascorbate reductase (MDHAR) in an NAD(P)H-dependent manner and by dehydroascorbate reductase (DHAR) employing GSH as electron donor. The resulting GSSG is reduced in turn to GSH by GR ( Foyer and Noctor, 2011 ).

Different Effects of NO in the Regulation of Antioxidant Enzymes

The application of NO donors alleviates oxidative stress in plants challenged to abiotic and/or biotic stresses ( Laxalt et al., 1997 ; Beligni and Lamattina, 1999b , 2002 ; Shi et al., 2007 ; Xue et al., 2007 ; Leitner et al., 2009 ).

Besides the direct ROS-scavenging activity of NO, its beneficial effect is exerted by the regulation of the antioxidant enzymes activity that controls toxic levels of ROS and RNS ( Uchida et al., 2002 ; Shi et al., 2005 ; Song et al., 2006 ; Romero-Puertas et al., 2007 ; Bai et al., 2011 ). NO can modulate cell redox balance in plants through the regulation of gene expression, posttranslational modification or by its binding to the heme prosthetic group of some antioxidant enzymes.

SOD catalyzes the dismutation of stress-generated O 2 •– in one of two less harmful species: either molecular oxygen (O 2 ) or hydrogen peroxide (H 2 O 2 ). APX and CAT are the most important enzymes degrading H 2 O 2 in plants. They transform H 2 O 2 to H 2 O and O 2 . APX isoforms are primarily found in the cytosol and chloroplasts, while the CAT isoforms are found in peroxisomes. APX has strong affinity for H 2 O 2 and uses ASC as an electron donor. In contrast, CAT removes H 2 O 2 generated in the peroxisomal respiratory pathway without the need to reduce power. Even though CAT affinity for H 2 O 2 is low, its elevated rate of reaction offers an effective way to detoxify H 2 O 2 inside the cell. PRX may reduce both hydroperoxide and peroxynitrite.

Many reports on different plant species demonstrate that NO induces the transcription and activity of antioxidative enzymes in response to oxidative stress. The tolerance to drought and salt-induced oxidative stress in tobacco is related to the ABA-triggered production of H 2 O 2 and NO. In turn, they induce transcripts and activities of SOD, CAT, APX, and GR ( Zhang et al., 2009 ). UV-B-produced oxidative stress in Glycine max was alleviated by NO donors, which induced transcription and activities of SOD, CAT, and APX ( Santa-Cruz et al., 2014 ). Furthermore, in bean leaves, SOD, CAT, and APX activities are increased by NO donors, and protected from the oxidative stress generated by UV-B irradiation ( Shi et al., 2005 ). Drought tolerance in bermudagrass is improved by ABA-dependent SOD and CAT activities. This effect is regulated by H 2 O 2 and NO, NO acting downstream H 2 O 2 ( Lu et al., 2009 ).

Several antioxidant enzymes have been identified as target of S-nitrosylation, resulting in a change of their biological activity ( Romero-Puertas et al., 2008 ; Bai et al., 2011 ; Fares et al., 2011 ). For instance, NO reinforces recalcitrant seed desiccation tolerance in Antiaris toxicaria by activating the ascorbate-glutathione cycle through S-nitrosylation to control H 2 O 2 accumulation. Desiccation treatment reduced the level of S-nitrosylated APX, GR, and DHAR proteins. Instead, NO gas exposure activated them by S-nitrosylation ( Bai et al., 2011 ). Furthermore, APX was S-nitrosylated at Cys32 during saline stress and biotic stress, enhancing its enzymatic activity ( Begara-Morales et al., 2014 ; Yang et al., 2015 ). In addition, auxin-induced denitrosylation of cytosolic APX provoked inhibition of its activity, followed by an increase of H 2 O 2 concentration and the consequent lateral root formation in Arabidopsis ( Correa-Aragunde et al., 2013 ). Moreover, an inhibitory impact of S-nitrosylation on APX activity was also reported during programmed cell death in Arabidopsis ( de Pinto et al., 2013 ). CAT was identified to be S-nitrosylated in a proteomic study of isolated peroxisomes ( Ortega-Galisteo et al., 2012 ). A decrease of S-nitrosylated CAT under Cd treatment was reported. In addition, in vitro experiments demonstrated a reversible inhibitory effect of APX and CAT activities by NO binding to the Fe of the heme cofactor ( Brown, 1995 ; Clark et al., 2000 ). In addition, NOXs have been involved in plant defense, development, hormone biosynthesis and signaling ( Marino et al., 2012 ). Whereas S-nitrosylation did not affect SOD activities, nitration inhibited Mn-SOD1, Fe-SOD3, and CuZn-SOD3 activity to different degrees ( Holzmeister et al., 2015 ). SOD isoforms could also regulate endogenous NO availability by competing for the common substrate, O 2 •– , and it was demonstrated that bovine SOD may release NO from GSNO ( Singh et al., 1999 ). When GSNO is decomposed by GSNOR, it produces GSSG. GSNOR is also regulated by NO. Frungillo et al. (2014) demonstrated that NO-derived from nitrate assimilation in Arabidopsis inhibited GSNOR1 by S-nitrosylation, preventing GSNO degradation. They proposed that (S)NO controls its own generation and scavenging by modulating nitrate assimilation and GSNOR1 activity. It was also shown that chilling treatment in poplar increased S-nitrosylation of NR, along with a significant decrease of its activity ( Cheng et al., 2015 ).

The dual activity of Prx, suggests a role for this enzyme both in ROS and RNS regulation. S-nitrosylation of Arabidopsis PrxIIE inhibits its peroxynitrite activity, increasing peroxynitrite-mediated tyrosine nitration ( Romero-Puertas et al., 2007 ). Pea mitochondrial PrxIIF was S-nitrosylated under salt stress, and its peroxidase activity was reduced by 5 mM GSNO ( Camejo et al., 2013 ).

An interesting study demonstrated that NO controls hypersensitive response (HR) through S-nitrosylation of NOX, inhibiting ROS synthesis. This triggers a feedback loop limiting HR ( Yun et al., 2011 ).

Other proteins related to abiotic stress response are regulated by S-nitrosylation (For a review see Fancy et al., 2017 ).

Figure Figure3 3 is a simplified diagram that illustrates the main oxidative and nitrosative effects that modulate the activities of key cell components, thus maintaining cell redox balance. Note the feedback and positive-negative regulatory processes occurring in the main pathways. They involve posttranslational modifications that activate and inhibit the components involved in cell antioxidant system.

An external file that holds a picture, illustration, etc.
Object name is fpls-09-00273-g003.jpg

Molecules and mechanisms involved in NO-mediated redox balance. H 2 O 2 is generated mainly by NOX and SOD as a response to (a)biotic stress. APX and CAT are the main H 2 O 2 -degrading enzymes. NO is increased by H 2 O 2 through the induction of NR/NOS-like activities, and may scavenge ROS or induce both the transcription and activity of SOD, CAT, and APX. In parallel, NO is combined with GSH to form nitrosoglutathione GSNO. GSNO regulates many enzymatic activities by the posttranslational modification of cysteine residues through S-Nitrosylation. NOX and CAT activities are inhibited by S-nitrosylation, whereas APX is either activated or inhibited by S-nitrosylation. NO also inhibits APX by binding to heme group. GSNO is degraded by GSNOR, which could be inhibited by H 2 O 2 and S-nitrosylation.NR could be inhibited by S-nitrosylation. GR reduces GSSG to GSH, and it is activated by S-nitrosylation. Ascorbate (ASC) is a cofactor of APX. Reduced ASC is generated by MDHAR and DHAR, using GSH as electron donor. Both enzymes are inhibited by S-nitrosylation. Reactive Nitrogen Species (RNS) may be originated by NO and O 2 •– reaction. SOD regulate RNS dismutating O 2 •– . Peroxiredoxins (Prx) reduce both ROS AND RNS. RNS are degraded by PrxIIe, and H 2 O 2 by PrxIIF. Both enzymes are inhibited by S-nitrosylation. Red lines: H 2 O 2 -regulated reactions. Purple lines: NO-regulated reactions. Green lines: GSNO-regulated reactions.

Conclusions and Perspectives

The accelerating rate of climate change, together with habitat fragmentation caused by human activity, are part of the selective pressures building a new Earth’s landscape.

Climate change is a multidimensional and simultaneous variation in duration, frequency and intensity of parameters like temperature and precipitation, altering the seasons and life on the Earth. In this scenario, plant species with increased adaptive plasticity will be better equipped to tolerate changes in the frequency of extreme weather events. GHG are one of the forces driving climate change. However, CO 2 and NO may contribute to maintaining the cell redox homeostasis, regulating the amount of ROS, GSH, GSNO, and SNO.

In this manuscript, we summarize the available evidence supporting the presence of broad spectrum anti-stress molecules, as NO in plants, for coping with unprecedented changes in environmental conditions. Future research should focus in better understanding the influence of GHG on plant physiology.

Author Contributions

RC conceived the project and wrote the manuscript. MN drew figures and collaborated in writing the manuscript. NC-A and LL supervised and complemented the drafting. All the persons entitled to authorship have been named and have approved the final version of the submitted manuscript.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer MCR-P and handling Editor declared their shared affiliation.

Acknowledgments

We thank ANPCYT for MN fellowship. We also thank Marta Terrazo for helping with the language revision of the manuscript.

Funding. This work was supported by grants from the Consejo Nacional de Investigaciones Cientificas y Tecnicas, the Agencia Nacional de Promoción Científica y Tecnológica, and the Universidad Nacional de Mar del Plata, Argentina. NC-A, LL, and RC are permanent members of the Scientific Research career of CONICET. MN is doctoral fellow of the ANPCYT.

1 https://ozonewatch.gsfc.nasa.gov/facts/ozone.html

AbdElgawad H., Farfan-Vignolo E. R., de Vos D., Asard H. (2015). Elevated CO2 mitigates drought and temperature-induced oxidative stress differently in grasses and legumes. Plant Sci. 231 1–10. 10.1016/j.plantsci.2014.11.001 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Apel K., Hirt H. (2004). Reactive oxygen species: metabolism, oxidative stress, and signal transduction. Annu. Rev. Plant Biol. 55 373–399. 10.1146/annurev.arplant.55.031903.141701 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Asgher M., Per T. S., Anjum S., Khan M., Masood A., Verna S., et al. (2017). “Contribution of glutathione in heavy metal stress tolerance in plants,” in Reactive Oxygen Species and Antioxidant Systems in Plants: Role and Regulation under Abiotic Stress eds Khan M., Khan N. (Singapore: Springer; ) 10.1007/978-981-10-5254-5_12 [ CrossRef ] [ Google Scholar ]
Bai X., Yang L., Tian M., Chen J., Shi J., Yang Y., et al. (2011). Nitric oxide enhances desiccation tolerance of recalcitrant Antiaris toxicaria seeds via protein S-nitrosylation and carbonylation. PLoS One 6 : e20714 . 10.1371/journal.pone.0020714 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Begara-Morales J. C., Sánchez-Calvo B., Chaki M., Valderrama R., Mata-Pérez C., López-Jaramillo J., et al. (2014). Dual regulation of cytosolic ascorbate peroxidase (APX) by tyrosine nitration and S -nitrosylation. J. Exp. Bot. 65 527–538. 10.1093/jxb/ert396 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Beligni M. V., Lamattina L. (1999a). Is nitric oxide toxic or protective? Trends Plant Sci. 4 299–300. 10.1016/S1360-1385(99)01451-X [ PubMed ] [ CrossRef ] [ Google Scholar ]
Beligni M. V., Lamattina L. (1999b). Nitric oxide protects against cellular damage produced by methylviologen herbicides in potato plants. Nitric Oxide 3 199–208. 10.1006/niox.1999.0222 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Beligni M. V., Lamattina L. (2002). Nitric oxide interferes with plant photo-oxidative stress by detoxifying reactive oxygen species. Plant Cell Environ. 25 737–748. 10.1046/j.1365-3040.2002.00857.x [ CrossRef ] [ Google Scholar ]
Blatt M. R. (2000). Cellular signaling and volume control in stomatal movements in plants. Annu. Rev. Cell Dev. Biol. 16 221–241. 10.1146/annurev.cellbio.16.1.221 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Brown G. C. (1995). Reversible binding and inhibition of catalase by nitric oxide. Eur. J. Biochem. 232 188–191. 10.1111/j.1432-1033.1995.tb20798.x [ PubMed ] [ CrossRef ] [ Google Scholar ]
Camejo D., Romero-Puertas M. D. C., Rodríguez-Serrano M., Sandalio L. M., Lázaro J. J., Jiménez A., et al. (2013). Salinity-induced changes in S-nitrosylation of pea mitochondrial proteins. J. Proteomics 79 87–99. 10.1016/j.jprot.2012.12.003 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Carvalho M. H. C. (2008). Drought stress and reactive oxygen species. Plant Signal. Behav. 3 156–165. 10.4161/psb.3.3.5536 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Chamizo-Ampudia A., Sanz-Luque E., Llamas A., Ocana-Calahorro F., Mariscal V., Carreras A., et al. (2016). A dual system formed by the ARC and NR molybdoenzymes mediates nitrite-dependent NO production in Chlamydomonas . Plant Cell Environ. 39 2097–2107. 10.1111/pce.12739 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Cheng T., Chen J., Ef A. A., Wang P., Wang G., Hu X., et al. (2015). Quantitative proteomics analysis reveals that S-nitrosoglutathione reductase (GSNOR) and nitric oxide signaling enhance poplar defense against chilling stress. Planta 242 1361–1390. 10.1007/s00425-015-2374-5 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Choudhury F. K., Rivero R. M., Blumwald E., Mittler R. (2017). Reactive oxygen species, abiotic stress and stress combination. Plant J. 90 856–867. 10.1111/tpj.13299 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Ciais P., Reichstein M., Viovy N., Granier A., Ogée J., Allard V., et al. (2005). Europe-wide reduction in primary productivity caused by the heat and drought in 2003. Nature 437 529–533. 10.1038/nature03972 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Clark D., Durner J., Navarre D. A., Klessig D. F. (2000). Nitric oxide inhibition of tobacco catalase and ascorbate peroxidase. Mol. Plant. Microbe. Interact. 13 1380–1384. 10.1006/niox.1999.0222 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Corlett R. T., Westcott D. A. (2013). Will plant movements keep up with climate change? Trends Ecol. Evol. 28 482–488. 10.1016/j.tree.2013.04.003 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Corpas F. J., Alché J. D., Barroso J. B. (2013). Current overview of S-nitrosoglutathione (GSNO) in higher plants. Front. Plant Sci. 4 : 126 . 10.3389/fpls.2013.00126 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Corpas F. J., Leterrier M., Valderrama R., Airaki M., Chaki M., Palma J. M., et al. (2011). Nitric oxide imbalance provokes a nitrosative response in plants under abiotic stress. Plant Sci. 181 604–611. 10.1016/j.plantsci.2011.04.005 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Correa-Aragunde N., Foresi N., Delledonne M., Lamattina L. (2013). Auxin induces redox regulation of ascorbate peroxidase 1 activity by S-nitrosylation/denitrosylation balance resulting in changes of root growth pattern in Arabidopsis . J. Exp. Bot. 64 3339–3349. 10.1093/jxb/ert172 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Correa-Aragunde N., Foresi N., Lamattina L. (2015). Nitric oxide is a ubiquitous signal for maintaining redox balance in plant cells: regulation of ascorbate peroxidase as a case study. J. Exp. Bot. 66 2913–2921. 10.1093/jxb/erv073 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Chater C., Peng K., Movahedi M., Dunn J. A., Walker H. J., Liang Y. K., et al. (2015). Elevated CO 2 -induced responses in stomata require ABA and ABA signaling. Curr. Biol. 25 2709–2716. 10.1016/j.cub.2015.09.013 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
de Pinto M. C., Locato V., Sgobba A., Romero-Puertas M. D. C., Gadaleta C., Delledonne M., et al. (2013). S-Nitrosylation of ascorbate peroxidase is part of programmed cell death signaling in tobacco bright yellow-2 cells. Plant Physiol. 163 1766–1775. 10.1093/jxb/ert172 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Di Dato V., Musacchia F., Petrosino G., Patil S., Montresor M., Sanges R., et al. (2015). Transcriptome sequencing of three Pseudo-nitzschia species reveals comparable gene sets and the presence of nitric oxide synthase genes in diatoms. Sci. Rep. 5 : 12329 . 10.1038/srep12329 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Drake B. G., Gonzalez-Meler M. A., Long S. P. (1997). More efficient plants: a consequence of rising atmospheric CO 2 ? Annu. Rev. Plant Physiol. Plant Mol. Biol. 48 609–639. 10.1146/annurev.arplant.48.1.609 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Du S., Zhang R., Zhang P., Liu H., Yan M., Chen N., et al. (2016). Elevated CO 2 -induced production of nitric oxide (NO) by NO synthase differentially affects nitrate reductase activity in Arabidopsis plants under different nitrate supplies. J. Exp. Bot. 67 893–904. 10.1093/jxb/erv506 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Dubiella U., Seybold H., Durian G., Komander E., Lassig R., Witte C. P., et al. (2013). Calcium-dependent protein kinase/NADPH oxidase activation circuit is required for rapid defense signal propagation. Proc. Natl. Acad. Sci. U.S.A. 110 8744–8749. 10.1073/pnas.1221294110 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Fancy N. N., Bahlmann A. K., Loake G. J. (2017). Nitric oxide function in plant abiotic stress. Plant Cell Environ. 40 462–472. 10.1111/pce.12707 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Fares A., Rossignol M., Peltier J. (2011). Proteomics investigation of endogenous S-nitrosylation in Arabidopsis . Biochem. Biophys. Res. Commun. 416 331–336. 10.1038/srep12329 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Farnese F. S., Menezes-Silva P. E., Gusman G. S., Oliveira J. A. (2016). When bad guys become good ones: the key role of reactive oxygen species and Nitric Oxide in the plant responses to abiotic stress. Front. Plant Sci. 7 : 471 . 10.3389/fpls.2016.00471 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Foresi N., Correa-Aragunde N., Parisi G., Calo G., Salerno G., Lamattina L. (2010). Characterization of a nitric oxide synthase from the plant kingdom: NO generation from the green alga Ostreococcus tauri is light irradiance and growth phase dependent. Plant Cell 22 3816–3830. 10.1105/tpc.109.073510 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Foyer C. H., Noctor G. (2011). Ascorbate and glutathione: the heart of the redox hub. Plant Physiol. 155 2–18. 10.1038/srep12329 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Frohlich A., Durner J. (2011). The hunt for plant nitric oxide synthase (NOS): Is one really needed? Plant Sci. 181 401–404. 10.1016/j.plantsci.2011.07.014 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Frohnmeyer H., Staiger D. (2003). Ultraviolet-B-radiation-mediated responses in plants. Balancing damage and protection. Plant Physiol. 133 1420–1428. 10.1104/pp.103.030049 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Frungillo L., Skelly M. J., Loake G. J., Spoel S. H., Salgado I. (2014). S-nitrosothiols regulate nitric oxide production and storage in plants through the nitrogen assimilation pathway. Nat. Commun. 5 : 5401 . 10.1038/ncomms6401 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
García-Mata C., Gay R., Sokolovski S., Hills A., Lamattina L., Blatt M. R. (2003). Nitric oxide regulates K + and Cl-channels in guard cells through a subset of abscisic acid-evoked signaling pathways. Proc. Natl. Acad. Sci. U.S.A. 100 11116–11121. 10.1073/pnas.1434381100 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
García-Mata C., Lamattina L. (2013). Gasotransmitters are emerging as new guard cell signaling molecules and regulators of leaf gas exchange. Plant Sci. 201-202 66–73. 10.3389/fpls.2016.00277 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Gregg J., Jones C., Dawson T. (2003). Urbanization effects on tree growth in the vicinity of New York City. Nature 424 183–187. 10.1038/nature01728 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Grill E., Löffler S., Winnacker E. L., Zenk M. H. (1989). Phytochelatins, the heavy-metal-binding peptides of plants, are synthesized from glutathione by a specific gamma-glutamylcysteine dipeptidyl transpeptidase (phytochelatin synthase). Proc. Natl. Acad. Sci. U.S.A. 86 6838–6842. 10.1038/srep12329 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Gupta K. J., Igamberdiev A. U. (2016). Reactive nitrogen species in mitochondria and their implications in plant energy status and hypoxic stress tolerance. Front. Plant Sci. 7 : 369 . 10.3389/fpls.2016.00369 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Hall S., Huber D., Grimm N. (2008). Soil N 2 O and NO emissions from an arid, urban ecosystem. J. Geophys. Res. 113 : G01016 10.1029/2007JG000523 [ CrossRef ] [ Google Scholar ]
Hasanuzzaman M., Nahar K., Alam M. M., Roychowdhury R., Fujita M. (2013). Physiological, biochemical, and molecular mechanisms of heat stress tolerance in plants. Int. J. Mol. Sci. 14 9643–9684. 10.3390/ijms14059643 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Held I., Souden B. (2000). Water vapor feedback and global warming. Annu. Rev. Energy Environ. 25 441–475. 10.1146/annurev.energy.25.1.441 [ CrossRef ] [ Google Scholar ]
Holzmeister C., Gaupels F., Geerlof A., Sarioglu H., Sattler M., Durner J., et al. (2015). Differential inhibition of Arabidopsis superoxide dismutases by peroxynitrite-mediated tyrosine nitration. J. Exp. Bot. 66 989–999. 10.1093/jxb/eru458 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
IPCC (2014). Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change eds Edenhofer O. R., Pichs-Madruga Y., Sokona E., Farahani S., Kadner K., Seyboth A., et al. Cambridge: Cambridge University Press. [ Google Scholar ]
Jeandroz S., Wipf D., Stuehr D. J., Lamattina L., Melkonian M., Tian Z., et al. (2016). Occurrence, structure, and evolution of nitric oxide synthase-like proteins in the plant kingdom. Sci. Signal. 9 : re2 . 10.1126/scisignal.aad4403 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Jhun I., Coull B. A., Zanobetti A., Koutrakis P. (2015). The impact of nitrogen oxides concentration decreases on ozone trends in the USA. Air Qual. Atmos. Health 8 283–292. 10.1088/1748-9326/10/8/084009 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Jin C. W., Du S. T., Chen W. W., Li G. X., Zhang Y. S., Zheng S. J. (2009). Elevated carbon dioxide improves plants iron nutrition through enhancing the iron-deficiency-induced responses under iron-limited conditions in tomato. Plant Physiol. 150 272–280. 10.1104/pp.109.136721 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Karl T. R., Trenberth K. E. (2003). Modern global climate change. Science 302 1719–1723. 10.1126/science.1090228 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Kiehl J., Trenberth K. (1997). Earth’s annual global mean energy budget. Bull. Amer. Meteor. Soc. 78 197–208. [ Google Scholar ]
Kim T., Böhmer M., Hu H., Nishimura N., Schroeder J. I. (2010). Guard cell signal transduction network: advances in understanding abscisic acid, CO 2 , and Ca 2+ signaling. Annu. Rev. Plant Biol. 61 561–591. 10.1146/annurev-arplant-042809-112226 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Kimball B. (2016). Crop responses to elevated CO 2 and interactions with H 2 O, N, and temperature. Curr. Opin. Plant Biol. 31 36–43. 10.1016/j.pbi.2016.03.006 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Königshofer H., Tromballa H. W., Löppert H. G. (2008). Early events in signaling high-temperature stress in tobacco BY2 cells involve alterations in membrane fluidity and enhanced hydrogen peroxide production. Plant Cell Environ. 31 1771–1780. 10.1111/j.1365-3040.2008.01880.x [ PubMed ] [ CrossRef ] [ Google Scholar ]
Kumar A., Castellano I., Patti F. P., Palumbo A., Buia M. C. (2015). Nitric oxide in marine photosynthetic organisms. Nitric Oxide 47 34–39. 10.1038/srep12329 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Kumari S., Agrawal M., Singh A. (2015). Effects of ambient and elevated CO 2 and ozone on physiological characteristics, antioxidative defense system and metabolites of potato in relation to ozone flux. Environ. Exp. Bot. 109 276–287. 10.1016/j.envexpbot.2014.06.015 [ CrossRef ] [ Google Scholar ]
Lamattina L., García-Mata C., Graziano M., Pagnussat G. (2003). Nitric oxide: the versatility of an extensive signal molecule. Annu. Rev. Plant Biol. 54 109–136. 10.1146/annurev.arplant.54.031902.134752 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Laxalt A. M., Beligni M. V., Lamattina L. (1997). Nitric oxide preserves the level of chlorophyll in potato leaves infected by Phytophthora infestans. Eur. J. Plant Pathol. 103 643–651. 10.1023/A:1008604410875 [ CrossRef ] [ Google Scholar ]
Le Treut H., Somerville R., Cubasch U., Ding Y., Mauritzen C., Mokssit A., et al. (2007). “Historical overview of climate change science,” in Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change eds Solomon S., Qin D., Manning M., Chen Z., Marquis M., Averyt K. B., et al. (Cambridge: Cambridge University Press; ). [ Google Scholar ]
Leimu R., Vergeer P., Angeloni F., Ouborg N. (2010). Habitat fragmentation, climate change, and inbreeding in plants. Ann. N. Y. Acad. Sci. 1195 84–98. 10.1111/j.1749-6632.2010.05450.x [ PubMed ] [ CrossRef ] [ Google Scholar ]
Leitner M., Vandelle E., Gaupels F., Bellin D., Delledonne M. (2009). NO signals in the haze: nitric oxide signalling in plant defence. Curr. Opin. Plant Biol. 12 451–458. 10.1016/j.pbi.2009.05.012 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Long S., Ainsworth E., Leakey A., Nösberger J., Ort D. (2006). Food for thought: lower-than-expected crop yield stimulation with rising CO 2 concentrations. Science 312 1918–1921. 10.1126/science.1114722 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Long S., Ainsworth E., Rogers A., Ort D. (2004). Rising atmospheric carbon dioxide: plants FACE the future. Annu. Rev. Plant Biol. 55 591–628. 10.1146/annurev.arplant.55.031903.141610 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Lu S., Su W., Li H., Guo Z. (2009). Abscisic acid improves drought tolerance of triploid bermudagrass and involves H 2 O 2 - and NO-induced antioxidant enzyme activities. Plant Physiol. Biochem. 7 132–138. 10.1016/j.plaphy.2008.10.006 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Marino D., Dunand C., Puppo A., Pauly N. (2012). A burst of plant NADPH oxidases. Trends Plant Sci. 17 9–15. 10.1016/j.tplants.2011.10.001 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Markelz R. J., Lai L. X., Vosseler L. N., Leakey A. D. (2014). Transcriptional reprogramming and stimulation of leaf respiration by elevated CO 2 concentration is diminished, but not eliminated, under limiting nitrogen supply. Plant Cell Environ. 37 886–988. 10.1111/pce.12205 [ PubMed ] [ CrossRef ] [ Google Scholar ]
McAdam E. L., Brodribb T. J., McAdam S. A. (2017). Does ozone increase ABA levels by non-enzymatic synthesis causing stomata to close? Plant Cell Environ. 40 741–747. 10.1111/pce.12893 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Medinets S., Skiba U., Rennenberg H., Butterbach-Bahl K. (2015). A review of soil NO transformation: associated processes and possible physiological significance on organisms. Soil Biol. Biochem. 80 92–117. 10.1016/j.soilbio.2014.09.025 [ CrossRef ] [ Google Scholar ]
Meyer C., Lea U. S., Provan F., Kaiser W. M., Lillo C. (2005). Is nitrate reductase a major player in the plant NO (nitric oxide) game? Photosynth. Res. 83 181–189. 10.1016/j.tplants.2011.10.001 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Mittler R., Blumwald E. (2010). Genetic engineering for modern agriculture: challenges and perspectives. Annu. Rev. Plant Biol. 61 443–462. 10.1146/annurev-arplant-042809-112116 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Mur L. A., Kenton P., Lloyd A. J., Ougham H., Prats E. (2008). The hypersensitive response; the centenary is upon us but how much do we know? J. Exp. Bot. 59 501–520. 10.1093/jxb/erm239 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Nicotra A., Atkin O., Bonser S., Davidson A., Finnegan E., Mathesius U., et al. (2010). Plant phenotypic plasticity in a changing climate. Trends Plant Sci. 15 684–692. 10.1016/j.tplants.2010.09.008 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Ortega-Galisteo A. P., Rodríguez-Serrano M., Pazmiño D. M., Gupta D. K., Sandalio L. M., Romero-Puertas M. C. (2012). S-Nitrosylated proteins in pea ( Pisum sativum L.) leaf peroxisomes: changes under abiotic stress. J. Exp. Bot. 63 2089–2103. 10.1016/j.tplants.2011.10.001 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Pilegaard K. (2013). Processes regulating nitric oxide emissions from soils. Philos. Trans. R. Soc. Lond. B Biol. Sci. 368 : 20130126 . 10.1098/rstb.2013.0126 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Qu A. L., Ding Y. F., Jiang Q., Zhu C. (2013). Molecular mechanisms of the plant heat stress response. Biochem. Biophys. Res. Commun. 432 203–207. 10.1016/j.bbrc.2013.01.104 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Rockel P., Strube F., Rockel A., Wildt J., Kaiser W. M. (2002). Regulation of nitric oxide (NO) production by plant nitrate reductase in vivo and in vitro. J. Exp. Bot. 53 103–110. 10.1093/jexbot/53.366.103 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Roelfsema M. R., Hedrich R., Geiger D. (2012). Anion channels: master switches of stress responses. Trends Plant Sci. 17 221–229. 10.1016/j.tplants.2012.01.009 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Romero-Puertas M. C., Campostrini N., Mattè A., Righetti P. G., Perazzolli M., Zolla L., et al. (2008). Proteomic analysis of S-nitrosylated proteins in Arabidopsis thaliana undergoing hypersensitive response. Proteomics 8 1459–1469. 10.1002/pmic.200700536 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Romero-Puertas M. C., Laxa M., Mattè A., Zaninotto F., Finkemeier I., Jones A. M. E., et al. (2007). S-nitrosylation of peroxiredoxin II E promotes peroxynitrite-mediated tyrosine nitration. Plant Cell 19 4120–4130. 10.1105/tpc.107.055061 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Rouhier N., Lemaire S. D., Jacquot J.-P. (2008). The role of glutathione in photosynthetic organisms: emerging functions for glutaredoxins and glutathionylation. Annu. Rev. Plant Biol. 59 143–166. 10.1146/annurev.arplant.59.032607.092811 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Santa-Cruz D., Pacienza N., Zilli C., Tomaro M., Balestrasse K., Yannarelli G. (2014). Nitric oxide induces specific isoforms of antioxidant enzymes in soybean leaves subjected to enhanced ultraviolet-B radiation. J. Photochem. Photobiol. B 141 202–209. 10.1016/j.jphotobiol.2014.09.019 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Scheffers B. R., De Meester L., Bridge T. C., Hoffmann A. A., Pandolfi J. M., Corlett R. T., et al. (2016). The broad footprint of climate change from genes to biomes to people. Science 354 : aaf7671 . 10.1126/science.aaf7671 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Schmidt G. A., Ruedy R. A., Miller R. L., Lacis A. A. (2010). Attribution of the present-day total greenhouse effect. J. Geophys. Res. 115 : D20106 10.1029/2010JD014287 [ CrossRef ] [ Google Scholar ]
Shi K., Li X., Zhang H., Zhang G., Liu Y., Zhou Y., et al. (2015). Guard cell hydrogen peroxide and nitric oxide mediate elevated CO 2 -induced stomatali movement in tomato. New Phytol. 208 342–353. 10.1111/nph.13621 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Shi Q., Ding F., Wang X., Wei M. (2007). Exogenous nitric oxide protect cucumber roots against oxidative stress induced by salt stress. Plant Physiol. Biochem. 45 542–550. 10.1016/j.plaphy.2007.05.005 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Shi S., Wang G., Wang Y., Zhang L., Zhang L. (2005). Protective effect of nitric oxide against oxidative stress under ultraviolet-B radiation. Nitric Oxide 13 1–9. 10.1016/j.niox.2005.04.006 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Singh R., Hogg N., Goss S., Antholine W., Kalyanaraman B. (1999). Mechanism of superoxide dismutase/H 2 O 2 -mediated nitric oxide release from S -nitrosoglutathione–role of glutamate. Arch. Biochem. Biophys. 372 8–15. 10.1006/abbi.1999.1447 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Smith N. G., Dukes J. S. (2013). Plant respiration and photosynthesis in global-scale models: incorporating acclimation to temperature and CO 2 . Glob. Change Biol. 19 45–63. 10.1111/j.1365-2486.2012.02797.x [ PubMed ] [ CrossRef ] [ Google Scholar ]
Soden B. J., Jackson D. L., Ramaswamy V., Schwarzkopf M. D., Huang X. (2005). The radiative signature of upper tropospheric moistening. Science 310 841–844. 10.1126/science.1115602 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Song L., Ding W., Zhao M., Sun B., Zhang L. (2006). Nitric oxide protects against oxidative stress under heat stress in the calluses from two ecotypes of reed. Plant Sci. 171 449–458. 10.1016/j.plantsci.2006.05.002 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Song Y., Miao Y., Song C. P. (2014). Behind the scenes: the roles of reactive oxygen species in guard cells. New Phytol. 201 1121–1140. 10.1111/nph.12565 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Stockwell C., Hendry A., Kinnison M. (2003). Contemporary evolution meets conservation. Trends Ecol. Evol. 18 94–101. 10.1016/S0169-5347(02)00044-7 [ CrossRef ] [ Google Scholar ]
Tossi V., Lamattina L., Cassia R. (2009). An increase in the concentration of abscisic acid is critical for nitric oxide-mediated plant adaptive responses to UV-B irradiation. New Phytol. 181 871–879. 10.1111/j.1469-8137.2008.02722.x [ PubMed ] [ CrossRef ] [ Google Scholar ]
Uchida A., Jagendorf A. T., Hibino T., Takabe T., Takabe T. (2002). Effects of hydrogen peroxide and nitric oxide on both salt and heat stress tolerance in rice. Plant Sci. 163 515–523. 10.1016/S0168-9452(02)00159-0 [ CrossRef ] [ Google Scholar ]
Vainonen J. P., Kangasjärvi J. (2015). Plant signalling in acute ozone exposure. Plant Cell Environ. 38 240–252. 10.1111/pce.12273 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Voesenek L. A., Bailey-Serres J. (2015). Flood adaptive traits and processes: an overview. New Phytol. 206 57–73. 10.1111/nph.13209 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Wang H., Xiao W., Niu Y., Chai R., Jin C., Zhang Y. (2015). Elevated carbon dioxide induces stomatal closure of Arabidopsis thaliana (L.) heynh. through an increased production of nitric oxide. J. Plant Growth Regul. 34 372–380. 10.1007/s00344-014-9473-6 [ CrossRef ] [ Google Scholar ]
Wuebbles D. J., Hayhoe K. (2002). Atmospheric methane and global change. Earth Sci. Rev. 57 177–210. 10.1016/S0012-8252(01)00062-9 [ CrossRef ] [ Google Scholar ]
Xie Y., Mao Y., Zhang W., Lai D., Wang Q., Shen W. (2014). Reactive oxygen species-dependent nitric oxide production contributes to hydrogen-promoted stomatal closure in Arabidopsis. Plant Physiol. 165 759–773. 10.1104/pp.114.237925 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Xu Z., Jiang Y., Jia B., Zhou G. (2016). Elevated-CO 2 response of stomata and its dependence on environmental factors. Front. Plant Sci. 7 : 657 . 10.3389/fpls.2016.00657 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Xu Z., Jiang Y., Zhou G. (2015). Response and adaptation of photosynthesis, respiration, and antioxidant systems to elevated CO 2 with environmental stress in plants. Front. Plant Sci. 6 : 701 . 10.3389/fpls.2015.00701 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Xue L., Li S., Sheng H., Feng H., Xu S., An L. (2007). Nitric oxide alleviates oxidative damage induced by enhanced ultraviolet-B radiation in cyanobacterium. Curr. Microbiol. 55 294–301. 10.1007/s00284-006-0621-5 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Yan W., Zhong Y., Shangguan Z. (2017). Contrasting responses of leaf stomatal characteristics to climate change: a considerable challenge to predict carbon and water cycles. Glob. Chang. Biol. 23 3781–3793. 10.1111/gcb.13654 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Yang H., Mu J., Chen L., Feng J., Hu J., Li L., et al. (2015). S -Nitrosylation positively regulates ascorbate peroxidase activity during plant stress responses. Plant Physiol. 167 1604–1615. 10.1104/pp.114.255216 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
Yun B.-W., Feechan A., Yin M., Saidi N. B., Le Bihan T., Yu M., et al. (2011). S-nitrosylation of NADPH oxidase regulates cell death in plant immunity. Nature 478 264–268. 10.1038/nature10427 [ PubMed ] [ CrossRef ] [ Google Scholar ]
Zhang Y., Tan J., Guo Z., Lu S., He S., Shu W., et al. (2009). Increased abscisic acid levels in transgenic tobacco over-expressing 9 cis-epoxycarotenoid dioxygenase influence H 2 O 2 and NO production and antioxidant defenses. Plant Cell Environ. 32 509–519. 10.1111/j.1365-3040.2009.01945.x [ PubMed ] [ CrossRef ] [ Google Scholar ]
Zinta G., AbdElgawad H., Domagalska M. A., Vergauwen L., Knapen D., Nijs I., et al. (2014). Physiological, biochemical, and genome-wide transcriptional analysis reveals that elevated CO 2 mitigates the impact of combined heat wave and drought stress in Arabidopsis thaliana at multiple organizational levels. Glob. Chang. Biol. 20 3670–3685. 10.1111/gcb.12626 [ PubMed ] [ CrossRef ] [ Google Scholar ]

IELTS Preparation with Liz: Free IELTS Tips and Lessons, 2024

Test Information FAQ
Band Scores
IELTS Candidate Success Tips
Computer IELTS: Pros & Cons
How to Prepare
Useful Links & Resources
Recommended Books
Writing Task 1
Writing Task 2
Speaking Part 1 Topics
Speaking Part 2 Topics
Speaking Part 3 Topics
100 Essay Questions
On The Day Tips
Top Results
Advanced IELTS

Environment Essay Titles

Below are examples of IELTS Environmental writing task 2 questions.

Human activity has had a negative impact on plants and animals around the world. Some people think that this cannot be changed, while others believe actions can be taken to bring about a change. Discuss both and give your opinion. (Reported 2017, Academic Test)

It is often said that governments spend too much money on projects to protect wildlife, while there are other problems that are more important? Do you agree or disagree? (Reported 2017, GT Test)

Some people think the best way to solve global environmental problems is to increase the cost of fuel. To what extent do you agree or disagree? (Reported 2017, Academic Test)

Some people think an international car-free day is an effective way to reduce air pollution. Others think there are more effective ways do to this. Discuss both sides and give your opinion. (Reported 2017, Academic Test)

While some people consider global warming to be the most pressing environmental problem which we have at the moment, others believe that deforestation has a more devastating impact on our world. Discuss both sides and give your opinion.

The government should reduce the amount of money spent on local environmental problems and instead increase funding into urgent and more threatening issues such as global warming. To what extent do you agree?

With increasing populations and ever growing urban centers, many countries are losing their natural beauty spots. What benefits are there to protecting places of natural beauty? How can this be solved?

Although many people value their public parks, this space could be better used for other purposes such as residential areas for the ever growing population or to develop business and boost economies. To what extent do you agree or disagree with this?

With deforestation, urban development and illegal hunting, many animal species are becoming endangered as they lose their habitat and some are even threatened to the point of extinction. Do you think it is important to protect animals? What measures can be taken to deal with this problem?

Global warming is one of the biggest threats to our environment. What causes global warming? What solutions are there to this problem?

Both governments and individuals are spending vast amounts of money protecting animals and their habitat. This money could be better spent dealing with fundamental issues in society such as poverty and health care. To what extent do you agree?

As a result of growth in some urban centers, the environment in those cities is deteriorating. How could this issue be tackled by both the government and individuals?

Some people think that current environmental issues are global problems and should therefore be dealt with by the government while others believe that these problems can only be tackled by individuals. Discuss both sides and give your opinion.

Global environmental issues are the responsibility of rich nations not of poorer nations. Do you agree with this opinion?

Many people believe that global environmental problems should be dealt with internationally rather than domestically. What is your opinion?

Many animals are being hunted to the brink of extinction in order to fulfil the demand and greed of mankind for decorative purposes as well as for other reasons, such as traditional medicine. How can this issue be tackled?

Restricting air travel is the only way to prevent air pollution. Do you agree?

Reported essay questions are from students who have taken their IELTS test. These questions may vary slightly in wording from the original question.

All Practice IELTS Essay Questions

Over 100 IELTS Essay Questions

Advanced IELTS Lessons & E-books

Click Below to Learn:

IELTS Test Information

Copyright Notice

Privacy Policy & Disclaimer

Click here: Privacy Policy
Click here: Disclaimer

Return to top of page

What Is the Future of Wind Energy?

This article was reviewed by a member of Caltech's Faculty .

Humans have used windmills to capture the force of the wind as mechanical energy for more than 1,300 years . Unlike early windmills, however, modern wind turbines use generators and other components to convert energy from the spinning blades into a smooth flow of AC electricity.

In the video below, Resnick Sustainability Institute researcher John Dabiri discusses the future of wind energy technology.

How much of global electricity demand is met by wind energy?

Wind energy is a small but fast-growing fraction of electricity production. It accounts for 5 percent of global electricity production and 8 percent of the U.S. electricity supply.

Globally, wind energy capacity surpasses 743 gigawatts , which is more than is available from grid-connected solar energy and about half as much as hydropower can provide. Nearly three-quarters of that 651 gigawatts comes from wind farms in five countries: China, the U.S., Germany, India, and Spain. Wind energy capacity in the Americas has tripled over the past decade.

In the U.S., wind is now a dominant renewable energy source , with enough wind turbines to generate more than 100 million watts, or megawatts, of electricity, equivalent to the consumption of about 29 million average homes.

The cost of wind energy has plummeted over the past decade. In the U.S., it is cost-competitive with natural gas and solar power.

Wind energy and solar energy complement each other, because wind is often strongest after the sun has heated the ground for a time. Warm air rises from the most heated areas, leaving a void where other air can rush in, which produces horizontal wind currents . We can draw on solar energy during the earlier parts of the day and turn to wind energy in the evening and night. Wind energy has added value in areas that are too cloudy or dark for strong solar energy production, especially at higher latitudes.

How big are wind turbines and how much electricity can they generate?

Typical utility-scale land-based wind turbines are about 250 feet tall and have an average capacity of 2.55 megawatts, each producing enough electricity for hundreds of homes. While land-based wind farms may be remote, most are easy to access and connect to existing power grids.

Smaller turbines, often used in distributed systems that generate power for local use rather than for sale, average about 100 feet tall and produce between 5 and 100 kilowatts.

One type of offshore wind turbine currently in development stands 853 feet tall, four-fifths the height of the Eiffel Tower, and can produce 13 megawatts of power. Adjusted for variations in wind, that is enough to consistently power thousands of homes. While tall offshore turbines lack some of the advantages of land-based wind farms, use of them is burgeoning because they can capture the energy of powerful, reliable winds high in the air near coastlines, where most of the largest cities in the world are located.

What are some potential future wind technologies other than turbines?

Engineers are in the early stages of creating airborne wind turbines , in which the components are either floated by a gas like helium or use their own aerodynamics to stay high in the air, where wind is stronger. These systems are being considered for offshore use, where it is expensive and difficult to install conventional wind turbines on tall towers.

Trees, which can withstand gale forces and yet move in response to breezes from any direction, also are inspiring new ideas for wind energy technology. Engineers speculate about making artificial wind-harvesting trees . That would require new materials and devices that could convert energy from a tree's complex movements into the steady rotation that traditional generators need. The prize is wind energy harvested closer to the ground with smaller, less obtrusive technologies and in places with complex airflows, such as cities.

What are the challenges of using wind energy?

Extreme winds challenge turbine designers. Engineers have to create systems that will start generating energy at relatively low wind speeds and also can survive extremely strong winds. A strong gale contains 1,000 times more power than a light breeze, and engineers don't yet know how to design electrical generators or turbine blades that can efficiently capture such a broad range of input wind power. To be safe, turbines may be overbuilt to withstand winds they will not experience at many sites, driving up costs and material use. One potential solution is the use of long-term weather forecasting and AI to better predict the wind resources at individual locations and inform designs for turbines that suit those sites.

Climate change will bring more incidents of unusual weather, including potential changes in wind patterns . Wind farms may help mitigate some of the harmful effects of climate change. For example, turbines in cold regions are routinely winterized to keep working in icy weather when other systems may fail, and studies have demonstrated that offshore wind farms may reduce the damage caused by hurricanes . A more challenging situation will arise if wind patterns shift significantly. The financing for wind energy projects depends critically on the ability to predict wind resources at specific sites decades into the future. One potential way to mitigate unexpected, climate-change-related losses or gains of wind is to flexibly add and remove groups of smaller turbines, such as vertical-axis wind turbines , within existing large-scale wind farms.

Wind farms do have environmental impacts . The most well-known is harm to wildlife, including birds and bats . Studies are informing wind farm siting and management practices that minimize harm to wildlife , and Audubon, a bird conservation group, now supports well-planned wind farms. The construction and maintenance of wind farms involves energy-intensive activities such as trucking, road-building, concrete production, and steel construction. Also, while towers can be recycled, turbine blades are not easily recyclable. In hopes of developing low-to-zero-waste wind farms, scientists aim to design new reuse and disposal strategies , and recyclable plastic turbine blades. Studies show that wind energy's carbon footprint is quickly offset by the electricity it generates and is among the lowest of any energy source .

Dive Deeper

Wind Vision: A New Era for Wind Power in the United States

illustration of people working together to create light from plants, wind turbines, gears, and recyclable material

Caltech Energy 10 to Develop the Roadmap for 50% Reduction in Emissions by 2030

Tweaking Turbine Angles Squeezes More Power Out of Wind Farms

COMMENTS

Disadvantages vs. Advantages of Global Warming
Disadvantages: Land Desertification. As weather patterns are disrupted and droughts intensify in duration and frequency, agricultural sectors are particularly hard hit. Crops and grasslands can't thrive due to lack of water. With crops unavailable, cattle, sheep, and other livestock don't get fed and die.
Global Warming Essay: Causes, Effects, and Prevention
A. One degree in temperature change may not seem like a lot, but that amount of global warming can cause major crises, displacing millions of people and causing billions of dollars in damage. B. It is a known fact that fossil fuel burning, particularly coal, is the biggest culprit of global warming (MacMillan, 2016).
Essay on Global Warming with Samples (150, 250, 500 Words
Global warming is the unusually rapid increase in Earth's average surface temperature over the past century, primarily due to the greenhouse gases released by people burning fossil fuels. The greenhouse gases consist of methane, nitrous oxide, ozone, carbon dioxide, water vapour, and chlorofluorocarbons. The weather prediction has been ...
Global warming
Modern global warming is the result of an increase in magnitude of the so-called greenhouse effect, a warming of Earth's surface and lower atmosphere caused by the presence of water vapour, carbon dioxide, methane, nitrous oxides, and other greenhouse gases. In 2014 the IPCC first reported that concentrations of carbon dioxide, methane, and ...
What are the effects of global warming?
One global warming solution that was once considered far fetched is now being taken more seriously: geoengineering. This type of technology relies on manipulating the Earth's atmosphere to ...
Global Warming
Global warming is the long-term warming of the planet's overall temperature. Though this warming trend has been going on for a long time, its pace has significantly increased in the last hundred years due to the burning of fossil fuels.As the human population has increased, so has the volume of . fossil fuels burned.. Fossil fuels include coal, oil, and natural gas, and burning them causes ...
The Science of Climate Change Explained: Facts, Evidence and Proof
Average global temperatures have increased by 2.2 degrees Fahrenheit, or 1.2 degrees Celsius, since 1880, with the greatest changes happening in the late 20th century. Land areas have warmed more ...
Causes and effects of global warming
global warming, Increase in the global average surface temperature resulting from enhancement of the greenhouse effect, primarily by air pollution.In 2007 the UN Intergovernmental Panel on Climate Change forecast that by 2100 global average surface temperatures would increase 3.2-7.2 °F (1.8-4.0 °C), depending on a range of scenarios for greenhouse gas emissions, and stated that it was ...
Global Warming Advantages
Advantages. Global warming can change the climatic conditions and atmospheric temperature of the earth. Severe cold zones will experience warm climate which can enhance plant and animal growth in that regions (Global Warming: Pros & Cons). The temperature required to warm the frozen areas will come down due to global warming.
Are there positive benefits from global warming?
Published October 29, 2020. Yes, there will probably be some short-term and long-term benefits from global warming. For example, the flip side of increased mortality from heat waves may be decreased mortality from cold waves. In the short term, farmers in some regions may benefit from the earlier onset of spring and from a longer warm season ...
Global Warming Essay
A rise in global temperatures can lead to additional changes in the environment, such as rising sea levels. Since an increase in the temperature causes the glaciers and icebergs to melt at a rapid pace, it causes the sea levels to rise. On the Weather: Global Warming causes intense heat waves by significantly increasing the temperature which ...
Renewable energy, facts and information
Hydropower: For centuries, people have harnessed the energy of river currents, using dams to control water flow. Hydropower is the world's biggest source of renewable energy by far, with China ...
The huge benefits, and risks, of going for net zero emissions
Transitioning the global economy to net-zero emissions by midcentury would have high upfront costs, but huge benefits in the form of reduced climate damage and industrial innovations, two new reports out today show. Why it matters: The reports each detail the enormous upsides to limiting global warming's severity, along with the growing perils ...
Top 10 Benefits of Climate Action
Climate change is one of the most urgent issues of our day. Several recent studies show that acting quickly and decisively to address this challenge and shift our economy to clean energy will bring significant benefits to the United States—while also helping us avoid some of the worst consequences of unchecked global warming.
Advantages And Disadvantages Of Climate Change Essay
Advantages And Disadvantages Of Climate Change Essay. It is highly obvious that climate change is happening in most countries. In more detail, global temperatures have been rising for over a century, speeding up in the last few years, contributing to global warming. If that continues, disastrous scenarios can happen, but it is definitely not ...
The pros and cons of planting trees to address global warming
Authors of a 2019 study from the Swiss research university, ETH Zurich, estimated that the planet can support about 2.5 billion more acres of newly planted trees - without tearing down cities and doing away with farms. And they say those trees could store about 200 gigatons of carbon (GtC) once they mature.
Climate Change and the Impact of Greenhouse Gasses: CO
CO 2 Increasing: Advantages and Disadvantages. ... That envisages potential advantages for the C4 species in future climatic change scenarios, particularly in arid and semiarid areas. ... Water vapor feedback and global warming. Annu. Rev. Energy Environ. 25 441-475. 10.1146/annurev.energy.25.1.441 ...
Environment Essay Titles
Environment Essay Titles. Below are examples of IELTS Environmental writing task 2 questions. Human activity has had a negative impact on plants and animals around the world. Some people think that this cannot be changed, while others believe actions can be taken to bring about a change. Discuss both and give your opinion.
Analysis on Advantages and Disadvantages of Global Warming and Cooling
Climate change is a hot topic in modern society,as global warming is detected for last 100 years.Intergovernment Panel on Climate Change(IPCC)believed that human activities played an important role in contribution to global warming.Now people seem afraid very much on the "global warming",as any natural disasters happen,no matter the disaster is flooding or drought,heat wave or cool snowing ...
The advantages and disadvantages of renewable energy
New developments in renewable energy are making headlines and inspiring hope in communities worldwide, from a remote Arctic village working to harness solar and wind power under challenging conditions to a U.S. Air Force base planning an advanced, utility-scale geothermal power system.. As much of the world grapples with mitigating the effects of climate change and global warming, innovation ...
Wind energy facts, advantages, and disadvantages
Wind energy is a small but fast-growing fraction of electricity production. It accounts for 5 percent of global electricity production and 8 percent of the U.S. electricity supply. Globally, wind energy capacity surpasses 743 gigawatts, which is more than is available from grid-connected solar energy and about half as much as hydropower can ...
The Advantages And Disadvantages Of Global Warming And...
The relevant disadvantages that could take place due to global warming consist of epidemic water shortages in already water scarce locations. The melting of the ice and arctic ice caps would increase flooding worldwide. Global warming has the potential to increase death and disease in human and animals from incapacitating heat waves.
Essay On Advantages And Disadvantages Of Global Warming
647 Words | 2 Pages. The amount of CO2 in a planet's atmosphere affects the temperature of the planet. As more and more CO2 builds up in the atmosphere, less heat can escape and the planet gets hotter. The CO2 traps radiation from the sun like a greenhouse. This is called global warming or the greenhouse effect.
Genetically Modified Food: Advantages and Disadvantages Essay
Moreover, genetically modified foods would make weeds resistant to herbicides. The effect of herbicides reduces while weed tolerance occurs and thus larger doses of herbicides are needed to inhibit the growth of weeds (Owen & Zelaya, 2005). Nevertheless, weeds grow faster and resistant to herbicides due to overusing herbicides.