Climate 101

Jason Smerdon, a climate scientist at the Lamont-Doherty Earth Observatory of Columbia University, said that there are many steps an individual can take to reduce their carbon footprint, the carbon dioxide emissions they have generated. These actions include eating less beef, switching to a renewable energy source such as installing solar panels, driving less, driving electric or hybrid cars and washing clothes in cold water. In reference to a carbon footprint study, the actions that caused the biggest reduction in carbon footprint, in order, were having one less child, living car free, taking one less transatlantic flight, buying green energy, switching to being car-free and eating a plant-based diet. 

However, he also noted that reducing one’s carbon footprint has only a minute influence in a society built on fossil fuels. The only way to help bring about systemic change is to influence policy makers to create climate-friendly solutions. Participating in collective action is one of the most important things an individual can do, he said. This means voting, running for office, contributing to nonprofits or participating in an activist group. 

“Even the most extreme individual choices don't put a dent in our overall global emissions in a way that they should because we are all operating within a system that's built on fossil fuels. So the only way that you change things systemically is by collective action,” he said. 

—Abby Weiss

While climate change warrants urgent action, most people do not respond well to being terrified and feeling hopeless about the climate crisis, said Christie Manning, an assistant professor of environmental studies and psychology at Macalester College.

“People have to be aware of the threat before they can take action,” she said, but cautioned that “there is a gray area where a realistic portrayal of the threat of climate change veers into a hopeless doomsday depiction. If people feel like it’s a lost cause, they aren’t going to change.” 

Many people tune out when they need to psychologically protect themselves from acknowledging something frightening or when they feel that there is nothing they can do to help, Manning said. People are more moved to action when they have a sense of efficacy and feel as though they have the support to engage in action, rather than being forced or guilted into participating, she added.

Social community norms also work to move people towards climate action, Manning said. “A sense of ‘This is what people like me are doing,’ is very effective in getting people involved,” she said. Creating these norms can involve modeling different ways of taking action and inviting people to participate. 

Per Espen Stoknes, a psychologist and economist, also thinks that modeling climate-friendly behavior in a visible way can help move others to respond. 

“If you can make it seem normal to live in a climate friendly way, you’re spreading social norms about taking climate science seriously. You’re using the social brain,” he said. 

People respond to various framings of the climate crisis, he added. Some people are more motivated by a sense of ethical and moral duty to protect the Earth, while others respond better to economic arguments for green infrastructure and growth. 

“Speak about all of the fantastic solutions we have, from solar energy to plant-based foods, to educating yourself on the issue,” Stoknes said. “Speak three times as much about the opportunities as we speak about the threats.” 

— Maddie Kornfeld

There really isn’t just one thing that can be done at the individual level, said Sean Sublette, a meteorologist with Climate Central. He put the climate crisis in perspective this way: “No one person fixes this, but no one person created it, either.”

That’s not to say there’s nothing that can be done at all. Individual actions, when adopted widely, can add up and have a real impact, Sublette said. “I always tell people, do what’s within your means,” he said.

Here’s some individual actions he suggests:

1. Drive Less: Combine errands into one trip or opt to walk or bike if an errand is nearby.
2. Don’t Waste Water: Even if you don’t live in a region where water is scarce, Sublette said, you can still reduce your energy consumption by using less hot water. Try to take shorter showers and wash dishes and clothes with cold water.
3. Don’t Waste Food: Rotting food in landfills emits methane, a potent greenhouse gas that accelerates global warming. Be deliberate about using up food so it doesn’t get thrown away.
4. Reduce the Use of Plastics: Stop buying single-use plastics and opt for a reusable water bottle. Plastics are made with petroleum, which is energy intensive to extract.
5. Plant a Tree: Not only can trees absorb excess carbon dioxide from the atmosphere, they also help cool urban environments.
6. Switch to Energy Efficient Light Bulbs: Replace incandescent bulbs with longer lasting, energy efficient LED bulbs.
7. Change Your Thermostat: Turning your heat just one degree lower or your air conditioning just one degree higher can help reduce your energy consumption.
8. Invest in Solar Panels or an Electric Vehicle: These are some more expensive options to reduce your carbon footprint, if you have the means.

Once you’ve begun, tell family, friends and colleagues about what individual actions you’re taking to combat the climate crisis and encourage them to join you, Sublette said. Getting others on board will help make the problem seem more manageable.

“It’s a big daunting concept of a problem to solve and nobody solves it by themselves,” he said. “It takes everybody to do a little bit where you can.”   

—Katelyn Weisbrod

Regenerative agriculture does sequester carbon if the practices create a positive soil carbon budget, and by positive soil carbon budget, I mean the input of carbon into the soil must be more than the carbon losses from the soil,” said Rattan Lal, a professor of soil science at Ohio State University and recipient of the 2020 World Food Prize for his pioneering research on soil health.

Regenerative agriculture—sometimes called conservation or natural agriculture—can include a range of practices, but usually refers to things like cover cropping (planting winter soil with grasses), leaving crop residues on fields, using less or no chemical fertilizer and pesticide and not plowing up soil. When farmers employ these practices, they can help build healthier, more carbon-rich soil that more effectively draws carbon dioxide from the atmosphere and stashes away carbon.

The vast agricultural landscape of the American Midwest has significant potential. By Lal’s estimate, each acre could sequester up to 1,000 pounds of carbon a year, under optimal farming practices. 

Taking the country’s two largest crops—corn and soy—which are grown on about 163 million acres, that translates to a potential of about 74 million metric tons of carbon a year. 

Overall carbon emissions in the United States totaled about 1.5 gigatons in 2018. (Note that this is carbon; not carbon dioxide, which was about 5.4 gigatons.) So, according to Lal’s estimate, corn and soy acreage alone has the potential to offset 5 percent of U.S. emissions from fossil fuels.

That could potentially offset nearly half of emissions from all of U.S. agriculture.

Globally, Lal has estimated that soils could capture 180 gigatons of carbon between now and 2100, and up to 43 gigatons of that could be captured on cropland. 

A body of studies puts the annual sequestration potential on global crop and pasture lands at about 1.4  gigatons of carbon (or 5 gigatons of carbon dioxide). 

By comparison, carbon emissions from the fossil fuel industry, in 2019, were about 10 gigatons (or 37 gigatons of carbon dioxide). 

These figures represent the “technical potential” of soils, an amount of sequestration that’s theoretically feasible, not factoring in the significant economic, political and social hurdles.

Given these numbers, Lal and many other researchers say that soil carbon sequestration on agricultural land is not the “silver bullet” for controlling global greenhouse gas emissions. But, given the predicted upward trajectory for fossil fuel emissions, it is a critical, relatively easy and immediately deployable tool in the tool chest.

“Putting carbon into land buys us time until no-carbon fuel sources take effect,” Lal explained. “This is a bridge to the future.” 

— Georgina Gustin

Animal-based food, especially beef, produces more greenhouse gases than plant-based food because of the emissions released through its production, mostly at the farms and ranches where the animals are raised.

Grazing animals, especially cows, consume a lot of land, and in major beef-producing countries, especially the tropics, swathes of the rainforest are cut down to graze animals or to grow feed for those animals. That means forests that normally store carbon instead release carbon.

Ruminants, especially cows, also emit a lot of methane when they burp. (About 95 percent of the methane they emit comes from burps.) Methane and nitrous oxide, both potent greenhouse gases, are also released through their manure, and nitrous oxide is released from the use of nitrogen-based fertilizers, which are widely used to grow crops to feed livestock.

While beef is especially greenhouse-gas producing, animal-protein in general uses more resources through the production process, largely because of feed.

“What we can see pretty clearly is the big gap [in emissions] between plants and anything that’s animal based,” said Edwina Hughes, who helps run a program at the World Resources Institute (WRI) called the Cool Food Pledge, which encourages companies to assess the impact of the food they serve.

For example, Hughes said, producing beef uses 20 times the land and releases 20 times the greenhouse gas emissions, per gram of protein, than producing beans.  

The food system, in total, is a major contributor of greenhouse gases, producing about 35 percent of global emissions, according to the Food and Agriculture organization of the United Nations. Animal-based food accounts for two-thirds of that amount.

Researchers at WRI have calculated that, in order to curb climate change, consumers and producers need to cut about 67 percent of the climate impact of the food system by 2050.  Along with major reports from the IPCC and United Nations, they have emphasised the need to shift toward lower-impact, plant-based diets.

“We need to rebalance our plates,” Hughes said. 

—Georgina Gustin

The Arctic is warming more rapidly than anywhere else on Earth. This is caused by a process called “Arctic amplification.” As sea ice, glaciers and snow cover disappear, their reflective white surfaces melt away to reveal darker waters and land. The resulting decrease in surface reflectivity, known as albedo, causes the Arctic region to absorb more radiative energy from the sun, warming it faster than parts of the world without as much ice.

Rapid warming has widespread effects on seemingly all aspects of the Arctic environment. The 2020 Arctic Report Card described northward shifts in the ranges of Arctic species both on land, including moose and beaver, and in the ocean, including fish and plankton associated with harmful algal blooms. Some plant species are growing larger and expanding their ranges, affecting migratory bird breeding grounds. Wildfires are on the rise. And permafrost thaw puts large pools of carbon stored in frozen soils at risk of being released into the atmosphere, exacerbating climate change worldwide. These changes create a pervasive web of impacts that interact and feed back into one another.

The interconnected consequences of a warming Arctic affect people’s ways of life across northern latitudes and beyond. Thawing permafrost has damaged infrastructure and threatens to uproot communities that live near eroding coastlines. Changes in the jet stream alter weather patterns throughout the Northern Hemisphere. The melting of Greenland’s land ice contributes to sea level rise in more southerly coastal regions. Shifts in the Arctic Ocean affect not only local subsistence harvesting but also the global fish supply.

Jackie Richter-Menge, research affiliate at the University of Alaska Fairbanks and founding editor of the Arctic Report Card, said, “This is more than just being concerned about the physical environment. You need to be concerned about [Arctic change] because this is impacting you.”

The environmental changes also have political implications, said Lillian Hussong, the communications coordinator at The Arctic Institute and a doctoral candidate in global affairs at Rutgers University. Although nations, including Russia, are increasing military, political and economic activity in the Arctic, she said, the potential for conflict is often overplayed. “There's a lot of cooperation that happens in the Arctic that we aren't necessarily going to see elsewhere,” she said. “It's like a double-sided coin. There are such great concerns and yet at the same time, people and industries are still considering what kind of opportunities are there.”

While the changes are alarming, the extent of the damage is not set in stone, said Richter-Menge. “The fact that I could be witness to a change in the Earth's physical system over the 35 to 40 years that I've worked is mind-blowing,” Richter-Menge said. But, she added, a lot of effort is going into understanding ways to mitigate Arctic warming. “We know that it's going to take global action to change this. We just have to have the will to do it,” she said.

—Haley Dunleavy

Atmospheric “rivers” are streams of concentrated moisture in the atmosphere, said Katerina Gonzales, a climate scientist at Stanford University’s Climate and Earth System Dynamics Group.

They’re called “rivers'' partly because that’s what they look like on satellite images—long, relatively narrow bands of water—but also because they course through the atmosphere like a river moves across the landscape, Gonzales said.

These powerful rivers in the sky can carry massive volumes of water from the tropics toward the poles. When they bring moisture from regions near Hawaii to the West Coast, they’re often called the “pineapple express.”

“Atmospheric rivers often originate in the atmosphere over ocean basins and are carried along by different storm systems,” said Gonzales, who studies the causes and impacts of extreme precipitation in a warming climate. “When they cross over the ocean to land, they can induce extreme rates of rainfall, due to both the concentrated moisture and the strong winds in the atmospheric river."

Atmospheric rivers have caused most of the flooding in the western United States, scientists say. These raging rivers in the sky will become more intense as the planet warms.

As global temperatures increase, atmospheric rivers will become wetter, longer and wider, a trend that scientists say is already apparent. Even modest changes in intensity could lead to “significant increases in damages” from flooding, scientists reported in a 2019 study in Science Advances. “The increase in exposure to risk over the coming decades, as population in the western coastal states continues to grow, is likely to drive damages even higher,” the authors warned.

For more information, the National Oceanic & Atmospheric Administration curates an Atmospheric River Portal that provides detailed information as well as current conditions and forecasts related to these weather features. 

—Liza Gross

Simon Wang, a professor of climate dynamics at Utah State University, said scientific interest in the jet stream has intensified in the past few years but exactly how it influences extreme weather remains “inconclusive.” 

There are actually many jet streams, fast-flowing air currents found at various levels of the atmosphere that march west to east, redistributing energy around Earth in the form of cold and heat. The wavy amplitude of the airflow is partly influenced by temperature differentials that move the air currents from north to south, then south to north and so on. Extreme weather occurs when the waves get stuck in bottlenecks and stall.

Wang said the jet stream’s historical patterns are changing in part because the Arctic is warming faster than the tropics. Wang said the big question remains how much those changes are driving the extreme weather shifts. The scientific debate is especially fierce when it comes to winter in the northern hemisphere and the factors that influence the jet stream, including when mountains interrupt airflow, the comparatively larger proportion of land to water, and even pollution.

“I really prefer to say that the jet stream does not cause global warming,” Wang said. “It is responding to global warming or global cooling.” In the end, interactions from redistributed energy lead to extreme weather. 

—Judy Fahys

There’s little doubt that global warming will affect clouds, but since it’s very hard to measure the effects, it’s not clear if clouds reduce or increase the warming caused by carbon dioxide.

“Clouds have long been acknowledged to be the most unpredictable important part of the climate system,” said Matthew Huber, a climate scientist at Purdue University.

Some evidence suggests that the climate models used to project how human-caused climate change have underestimated climate feedback effects that can either enhance or weaken the warming caused by greenhouse gases. As a result, “there is a tendency to think that shiny, white, reflective clouds that cool the planet might diminish in a warmer world, or that the high, thin, heat-trapping clouds might be enhanced instead. But, the jury is still out,” Huber said.

This NASA video animation includes a good explanation of the role of clouds in the climate system, and the 2013 global climate assessment from the Intergovernmental Panel on Climate Change includes a detailed chapter on clouds. 

—Bob Berwyn 

“Climate and biodiversity are essentially two sides of the same coin,” said Pamela McElwee, an associate professor in the Department of Human Ecology at Rutgers University. 

Climate change directly and indirectly leads to declines in biodiversity, she said. Increased heat waves, extreme weather or wildfires can alter ecosystems, and can amplify other threats to biodiversity, like habitat loss. Biodiversity, meanwhile, helps moderate climate change. Oceans, forests, grasslands, wetlands and other ecosystems rich with life act like greenhouse gas sponges, absorbing about half of the carbon dioxide we emit, McElwee said. 

Because climate change and biodiversity are so intertwined, McElwee said, policies to address the two global issues must go hand-in-hand and cannot be treated separately.

McElwee recommends four big solutions to the climate and biodiversity problem, beginning with proper management of existing natural ecosystems, ensuring that those greenhouse gas sponges are thriving and absorbing carbon. Second, we should restore ecosystems that have been degraded from deforestation, agriculture, extraction and other human activities. Third, we should invest in nature-based solutions to climate change, like restoring wetlands and mangrove forests along coastlines instead of concrete seawalls and barriers to defend against sea level rise. Finally, McElwee said, we need to stop burning fossil fuels, which are driving climate change. 

“No matter what we do with ecosystems, it's not going to make for all that excess in terms of greenhouse gases,” McElwee said. 

—Katelyn Weisbrod

Peter Soroye, a biologist at the University of Ottawa, said that if pollinating insects die              off, it would drastically reshape life on Earth as we know it.

“Nearly 90 percent of flowering plants rely on animals to pollinate them,” he said. “The majority of these pollinators are insects like bees, wasps, butterflies, flies and beetles, although birds, bats and a few other animals also play a role in pollination.” Wind-pollinated plants, especially grasses, would still flower, but diversity would decline. Global warming is a big threat to pollinators. Bumblebees, for example, are very vulnerable to heat waves. 

And if pollinators died off, it would pose a threat to food supplies, since 70 of the most important 100 food crops require insect pollination, Soroye added.

Insects like bees pollinate many of the fruits, nuts and vegetables that are required for a nutritious diet. Berries, pumpkin, coffee and chocolate are just some of the foods that would disappear if we were to lose insect pollinators. Staples like corn, rice and wheat would remain, but our diets would become much less exciting. ”Picture eating spaghetti without ever having any tomato sauce,” he said. “Humans could begin hand pollinating or using robots to pollinate, but it would be very costly and difficult to do at the scale of insects.

Soroye added, “Across the globe insects are declining, including key pollinators like wild bumblebees, but a world without insect pollinators isn’t a reality we need to face. By addressing the main threats to these insects like habitat loss, climate change and pesticide use, we can begin to turn the tide on these declines.” 

—Bob Berwyn

Tim Searchinger is a research scholar at the Center for Policy Research on Energy and the Environment at the Woodrow Wilson School at Princeton University. He has been a longtime critic of biofuels and biofuels policy, publishing research more than a decade ago that challenged the idea of biofuels as a carbon neutral energy source.

Searchinger said most analyses that show a carbon benefit from biofuels don’t calculate the opportunity cost. 

“The basic way to think about it is: Biofuels are a way of using land to produce a plant to benefit the climate by replacing fossil fuels, but the cost is not using that land for some other purpose,” Searchinger explained. “Almost all the calculations that show benefits treat the land as free. They look at the benefits but not the cost.”

“We produce corn to eat, and if you’re not producing it in one place you have to produce it somewhere else,” Searchinger added.

Searchinger said that as biomass is diverted to biofuels, it triggers the clearing of forests or other lands to grow more corn, which are better at storing carbon than agricultural lands. This “indirect land-use change” effectively cancels out the greenhouse benefits of biofuels. 

Searchinger and his research colleagues said that studies showing a climate benefit fail to adequately account for the total carbon emitted through the biofuels life cycle. Much of that stems from an accounting mistake, in which the carbon emissions are counted only when biomass is harvested or cut, and not when it’s burned. 

“The usual explanation is that this carbon dioxide is automatically offset, that is, canceled out, by the carbon dioxide absorbed by plants when they grow,” Searchinger wrote in a sweeping 2019 report. “Because of this plant growth offset, the theory is that bioenergy does not add more carbon to the atmosphere, whereas burning fossil fuels adds new carbon to the air that would otherwise stay underground. Based on this theory, nearly all analyses estimating the climate benefits of bioenergy do not count the carbon dioxide released when biomass is burned.”

He also said that there’s no additional carbon absorption from growing corn on land where it’s already being grown. “That carbon absorption was going to happen anyway,” he explained. “Diverting it to ethanol doesn’t absorb more carbon.”

He added, “You can come up with extreme cases, with extreme assumptions, where you can claim a net gain, but then it’s a small percentage. Even then, the amount of carbon savings, per acre of land, of using biofuels is very small.” 

—Georgina Gustin

Daniel Raimi, a senior research associate at Resources for the Future and a lecturer at the Gerald R. Ford School of Public Policy at the University of Michigan, doesn’t think that breaking up major fossil fuel companies using anti-monopoly power is likely to make a big difference. 

Though Standard Oil, which in 1911 broke up after a federal lawsuit brought under the Sherman Antitrust Act, represented a textbook example of monopoly power, Raimi said, the fossil fuel industry looks very different today. 

Most oil and gas in the world is produced by government-owned and controlled companies. For that reason, Raimi said, “just breaking up the big oil companies we’ve all heard of,” like BP, Shell, Chevron and ExxonMobil, “might diminish their political power,” but it wouldn’t affect the global demand for oil and gas. That demand results in the fossil fuel production that largely drives global greenhouse gas emissions and, as a result, climate change. 

Raimi also distinguished breaking up large oil and gas companies from reducing the political influence of those companies. “There’s a real concern that energy companies have an outsized influence on shaping climate policy,” he said. Fossil fuel interests have outspent environmental advocates 10 to one lobbying on climate change legislation, according to an analysis by Robert J. Brulle, published in Climatic Change in 2018. 

But in Raimi’s mind, it’s not necessarily the size of energy companies that’s responsible for their influence. A company’s size “does not necessarily tell you anything about the likelihood of that company’s supporting climate policy,” he said.

While Raimi said that the solutions to addressing the obstruction of climate policy by fossil fuel interests were not in his area of expertise, the use of anti-monopoly power against fossil fuel companies was probably not a major solution to accelerating climate action. 

—Ilana Cohen

“I think that’s the question most people ask, and I don’t think that’s the best way to frame that question,” said Michael Vandenbergh, director of Vanderbilt Law School’s Climate Change Research Network. Rather, he said, “the question is, ‘What combination of public and private actions can reduce the risk of catastrophic climate change?’”

Because government response to climate change has been slow and inadequate, more people are turning to the private sector for solutions when it comes to reducing greenhouse gas emissions and safeguarding against the effects of global warming, Vandenbergh said. But that doesn’t mean private businesses can handle tackling the climate crisis on their own—far from it, he said.

The author of “Beyond Politics: The Private Governance Response to Climate Change,” Vandenbergh has spent more than a decade studying how the public and private sectors affect efforts to curb global warming. He said both must work in tandem to handle the enormous task of keeping warming below 2 degrees Celsius (3.7 degrees Fahrenheit) by the end of the century, which scientists say is necessary to prevent the worst of the climate crisis.

In some ways, that’s already happening, he said, even as the private sector takes a larger role, in part because the public sector isn’t doing enough. For example, he said, big tech companies like Google and Facebook have pressured some state governments to change how they regulate renewable energy, to allow the tech giants to build giant solar arrays to power their massive data banks.

Government also prompts actions from companies. When the federal government adopted new energy efficiency standards for light bulbs in 2007, Walmart announced it would make LED light bulbs its house brand, he said, increasing awareness of and sales for the product. LED bulbs use far less power and last much longer than the standard incandescent bulbs commonly used at the time.

As a result, the United States in 2018 reduced its carbon emissions by about 127 million metric tons, due to the electricity saved by the use of more energy efficient light bulbs, according to Vandenburgh’s research.

Despite those wins, Vandenburgh said, more government action at the federal, state and local levels is “essential” to tackling the climate crisis. “We need to get past the idea that any one response—whether private or public, federal, state or local—will solve the problem,” he said. “We need a collection of actions that can be adopted in the near term and will achieve major carbon reductions.” 

—Kristoffer Tigue

Hydrogen has become one of the hottest topics in the energy world, and Keith Wipke said it could play an important role in an emissions-free future. Wipke is the laboratory program manager for Fuel Cell and Hydrogen Technologies at the National Renewable Energy Laboratory, and he said their research suggests U.S. demand for hydrogen could double or even quadruple by 2050.

Most hydrogen is currently produced from natural gas, in a process that emits carbon dioxide. In order to be carbon-free, hydrogen would need to be made either from renewable electricity, such as wind or solar, or from natural gas paired with carbon capture and storage, which removes emissions and stores them underground. Both processes remain expensive. And even if gas were paired with carbon capture equipment, in order to be climate-neutral, companies would need to make sure no methane is leaking from the wells, tanks and pipelines that produce the fuel and carry it to market.

Today, hydrogen is used primarily in industrial processes, including oil refining. But Wipke said it has tremendous potential in heavy-duty transportation, from trucks to marine shipping or even aviation. These sectors are harder to electrify because of their long-haul demands: Batteries must either be extremely large and heavy or recharged frequently to carry that much power. Hydrogen could be used directly as a fuel in these vehicles, or in fuel-cells, which produce electricity. Wipke said hydrogen could also play an important role in removing emissions from some industrial processes, including steel manufacturing, and that it can be paired with biomass to produce chemicals and plastics.

“There’s basically a lot of places that hydrogen could be used that it’s not currently,” he said.

The outlook is more complicated in the electric power sector. Hydrogen is usually not a great option for generating power, Wipke said. It’s more efficient to simply make the electricity directly from either renewable sources or from natural gas with carbon capture and storage, rather than convert that electricity into hydrogen, transport it and then burn it in a power plant. But Wipke said it could play a role as a form of long-term storage, to make a renewables-powered grid more resilient. If the electric grid were powered largely by wind and solar, which are intermittent, it could help provide backup power when severe weather takes solar or wind sources offline for several days.

All told, Wipke said, his team’s research suggests that because of its versatility, hydrogen could make up from 4 percent to 17 percent of the energy system by 2050.

“They talk about hydrogen being the pocket-knife of the energy industry, it can do a lot of things,” he said. “It may not be the best blade at cutting things, but it also has scissors and it can open cans and saw wood. All these other things that a kitchen knife can’t do.” 

—Nicholas Kusnetz

Geothermal energy is usually produced by tapping into the Earth’s natural heating and cooling power in one of two ways: with power plants or with ground-source heat pumps, according to Chuck Kutscher, fellow and senior research associate at the University of Colorado’s Renewable and Sustainable Energy Institute. Geothermal plants power turbines to produce electricity, but instead of coal or natural gas, they use underground hot water (think geysers in Yellowstone National Park) or steam.

About five dozen geothermal plants produce just a small fraction of the nation’s electricity, just over a third of a percent, an output that’s been pretty steady over the last decade. Several of the Geysers units in Sonoma County, California, have been generating electricity for nearly a half century, while new plants are coming online in California to help that state meet its carbon-free, renewable energy goals.

On a smaller scale, ground-source heat pumps can be used anywhere to keep indoor spaces like homes and office buildings comfortable by carrying up cool air from underground during summer and warming them with underground heat during the winter. Kutscher said ground-source heat pumps are most cost-effective when they’re part of new building construction and for whole neighborhoods. 

“It's something that makes more sense for a new building than to retrofit an existing building,” he said, pointing to a development called the Whisper Valley Community in Texas where drilling, trenching and piping was done for many houses at once. “It becomes an economy of scale [with] all the houses heating and cooling more efficiently.”

These large- and small-scale technologies can both be used to facilitate the transition from coal and natural gas to emissions-free energy, he said. “As we get more solar and wind on the grid, and these are variable sources, the idea of having a constant source can be attractive.” 

—Judy Fahys

Dr. Aaron Bernstein, a pediatrician and Interim Director of The Center for Climate, Health, and the Global Environment at Harvard's T.H. Chan School of Public Health (Harvard C-CHANGE), said there is no direct evidence that climate change is one of the causes of the Covid-19 pandemic, specifically the spillover from a bat into a person. “We don’t know the origins of when and where it happened, even then there’s no distinguishable fingerprint of climate change,” he said.

But there are plenty of connections between climate change and the new coronavirus, in terms of who gets the disease, how sick one becomes and how to protect oneself. 

One link is that humans are moving into natural ecosystems which has increased our contact with wildlife and the diseases they carry. Tropical deforestation is one example of this phenomenon.  

“Where you're living and how you're living can make you vulnerable to the disease,” he said. “We know that this goes beyond the coronavirus. We know that chopping down forests, particularly in the tropics is a launchpad for disease spillover.” 

He said during the crisis over the Ebola virus, a fatal disease that occurs mainly in Africa, there was great concern that loss of tropical rainforest in Africa pushed bats closer to people, leading to more outbreaks. 

Air pollution, which is mainly from the burning of fossil fuels, not only perpetuates climate change but also the public’s susceptibility to the virus. Evidence has shown in multiple studies that there’s a strong likelihood that people who live in places with worse air pollution are more likely to contract the coronavirus and to die from it. 

Other issues associated with climate change, such as water scarcity, can prevent people from washing their hands, which is a main way to protect oneself from the virus.

—Abby Weiss

“There is no simple answer to this simple and important question,” said communications scientist Edward Maibach, of the George Mason University Center for Climate Change Communication.

Maibach said one of the most significant causes of climate denial has been the campaign by Exxon and other big fossil fuel industry leaders to sow doubt about the science of climate change, despite the fact that the companies knew as early as the 1970s that their products were causing global warming. 

“People who reject the conclusions of climate science have been deceived by people and institutions that they trust,” Maibach said. “The deception campaign took a long time, and a lot of money, but it has been wildly successful.”

Hundreds of millions of dollars from ExxonMobil, the Koch brothers and others have been used to fund groups like the Heartland Institute that aim to discredit climate scientists and delay policies that would help combat climate change. This disinformation was taken up by conservative Republicans, with political leaders like former President Trump continuing to spread falsehoods about climate change to their supporters. 

The campaign to discredit climate change was so successful, Maibach said, because it delivered “simple clear messages, repeated often, by a variety of voices who are trusted by the audience.”

Despite these efforts, scientists within the Trump administration fought back against this disinformation with guerilla-like tactics, Inside Climate News reported near the end of the Trump presidency, showing just one example of resistance against the climate denial machine. 

—Katelyn Weisbrod

This is the question that has driven the work of Tim Jackson, director of the Center for the Understanding of Sustainable Prosperity in the United Kingdom, and it’s one he explored when he served on the British government’s Sustainable Development Commission from 2004 to 2011.

“My answer to that question was, ultimately, you can’t.”

At the time, he said, the dominant theory among economists was that a market economy could achieve sustainability by “decoupling” growth from the use of materials and resources through efficiency and technological innovation, like renewable energy. This “decoupling” would allow an economy to grow even as greenhouse gas emissions fell. This view continues to hold sway among policymakers and mainstream economists, but there’s a growing movement of academics and advocates who argue that unlimited economic growth cannot be sustained on a planet with finite resources.

Rather than structuring the economy blindly around growth, Jackson argues, we should think about what services are provided by a particular business, investment or type of employment. Economic policy would then be structured to encourage those businesses and investments that deliver important services, rather than those that provide growth. Such a system might value a school teacher as much as or more than a trader of financial derivatives.

“This was a real lesson from the coronavirus pandemic,” he said. “The people who we felt were the least valuable people were the health workers, the care workers, the cleaners, the distribution people, the people on the front lines basically, who had been neglected, dispossessed, underpaid, underregarded in society for decades, because they weren’t productive in economic terms.” He added, "these people actually are the fundamental people who are providing for the quality of life in society in the most straightforward ways, and we neglect that sector of work at our peril."

More broadly, he said, the pandemic, which prompted massive government spending in response to collapsing economies, might help illuminate how the world could reshape the economy.

“The hope is that we can take the good bits of that and we can actually work our way around the bad bits of it—the insecurity that came through lockdown, and loss of jobs, and loss of livelihoods and social tension—and we can build a society that actually is a nice place to be, it’s a healthy, resilient, community-based society in which people do have livelihoods and they do have meaningful jobs.” 

—Nicholas Kusnetz

The number of ways to calculate the cost of climate change is growing, as scientists refine our understanding of climate impacts and those impacts play out. One measure in the United States is the National Oceanic and Atmospheric Administration’s ongoing billion-dollar disaster tally, which measures everything from the derecho that battered the Midwest with hurricane-force winds in 2020 to the drought plaguing the West, including the wildfires that scorched more acreage in California and Colorado in 2020 than ever before in recorded history. Large-scale weather disasters linked to climate change have been rising steadily, with the costs totaling $95 billion in 2020.

The insurance industry also keeps tabs on climate costs. The Swiss Re Group estimated that global insurance-industry losses in 2020 from natural catastrophes were $76 billion, making it the industry’s fifth-costliest year in a half-century.

But measures like these fail to take into account many significant losses, including the long-lasting psychological impacts of extreme weather events and the devastating costs to climate refugees. The World Economic Forum’s Global Risks Report also identifies biodiversity loss and ecosystem collapse as one of the top five threats humanity will face in the next decade. 

Akanksha Khatri, who leads the forum’s Nature Action Agenda in Geneva, points out that climate impacts to the natural world amount to roughly $13 trillion of the global economy. Construction, agriculture, food and beverages—they all depend on nature. Rainfall and weather linked to global warming, as well as the spread of invasive species, harms agriculture and the functioning of the bread baskets and rice bowls of the world.

“You're talking about 15 percent of the global GDP, which is directly impacted by climate change and nature loss,” she said.

Meanwhile, the Fourth National Climate Assessment cites research suggesting that, in the worst-case scenario, global warming costs could total 10 percent of U.S. GDP by the end of the century. And, by reducing emissions from their current high rate (RCP 8.5) to lower levels by midcentury (RCP 4.5), the estimated costs of climate change could be reduced from $494 billion annually to nearly $217 billion.

Khatri sees opportunity in the food, land and ocean sector, as well as risk. She estimates that this sector by itself could yield about $3.6 trillion of additional annual revenues or cost savings by 2030 as well as creating 191 million new jobs. But looking towards the economy as a whole, taking action that leads to net-zero emissions and other practices that are positive for the climate and nature could open the door to $10.1 trillion in opportunities and 395 million jobs by transitioning away from business-as-usual, her research shows.

“So I think anyone who says it is being done at the cost of economic growth, it's not really true,” she said. “It requires a systems transformation and moving away from this extractive fossil-fuel based economy that frankly, all of us are addicted to.”

Khatri pointed to recent successes in addressing the global pandemic and the prospect of cooperation in upcoming climate talks as reasons for optimism. “I really believe that as humanity, we can fix it. Just look at what we've been able to do with Covid,” she said. 

—Judy Fahys

One significant impact of climate change is drought—a lack of precipitation coupled with heat that speeds up evaporation and leaves the landscape primed for wildfire. Of course, drought has always made periodic appearances in the American West, but warming global temperatures associated with human-driven climate change is increasing the frequency and impacts of drought. This year, the West is struggling with a “megadrought,” defined as a drought lasting two decades or more.

Some scientific models suggest that climate change could bring more precipitation to the West. But, even if that were the case, the higher temperatures that climate models seem to agree on will also mean drier conditions, said Becky Bolinger, assistant state climatologist with the Colorado Climate Center at Colorado State University.

“When you're adding on more heat, you're probably evaporating more into the air and losing more moisture from the soils than what you would if the temperatures weren't as hot,” she said, pointing to earlier snowmelt and more evaporation. “You're still going to be at risk for drought, simply based on warmer temperatures.”

In the West, snowpack is more important for water availability and supply than rainfall events, Bolinger added. That’s because the frozen water in the mountains acts as a kind of freezer that allows the melting snow to gradually fill streams and reservoirs that humans, wildlife and the environment have evolved to rely on through the summer.

“You could get the same amount of snowpack as you've always gotten, but if you warm the temperatures, then when the snow melt time period begins in the spring, it could run off earlier and run off faster and more of it could be lost to evaporation,” she said, pointing out that that leaves less for water supplies struggling to recover between drought years. 

As heat wave after heat wave baked the West in 2021 during the region’s hottest June ever recorded, drought deepened and spread. By mid-July, nearly two thirds of the region was in extreme or exceptional drought, according to government data. And the nation’s two largest reservoirs, Lake Powell and Lake Mead, fell to near-record low levels and prompted leaders to cut water allocations to the 40 million people in seven states who rely on the lakes for water.

In addition, the dryness dug in, creating moisture deficits that, according to new research, go hand in hand with higher temperatures. Tinder-dry conditions meant an even greater risk of wildfire in a region that had already seen more than 1 million acres burned by wildfire.

“Evaporative demand and wildfire go hand in hand when you're talking weather,” said Bolinger, whose state endured the largest two wildfires in its history last year. “If you have a hot day and a dry day, and then you add wind, you have really high evaporative demand and a higher risk for wildfires spreading out of control at the same time.”

—Judy Fahys

According to the National Oceanic and Atmospheric Administration, the polar vortex that affects people in the Northern Hemisphere is a fast belt of westerly winds, between about 10 and 30 miles high, that intensify every winter, enclosing a large pool of extremely cold air over the North Pole and central Arctic Ocean. (There is an even stronger polar vortex in the Southern Hemisphere stratosphere during its winter.) When the vortex wobbles or expands, the cold air spills southward, causing cold snaps in North America, Europe or Asia.

Most recently, a kink in the polar vortex probably played a role in the deadly February 2021 outbreak of cold weather in the Southern Plains that caused massive power outages in Texas. NOAA climate researcher Amy Butler wrote in a blog post that the polar vortex “got stretched out of shape and slid southward off the pole.”

Scientists can’t yet tell for certain if global warming will disrupt the polar vortex more frequently, but there are several plausible theories for how that might happen, including how  shrinking sea ice affects the path of atmospheric waves that can shift the vortex if they are warm and high enough. 

—Bob Berwyn

Hurricanes have become a symbol for climate change and a rallying call for action. That’s especially the case since 2005, when Hurricane Katrina barreled into Louisiana and breached New Orleans levees, leaving behind an official death toll of 1,833.

Scientists found little evidence that climate change played any role in the wind speed intensity of Katrina, as well as Hurricane Irma in 2017 or Hurricane Maria in 2017, but they did pin increases in rainfall in those storms on climate change, according to the United Nations’ Intergovernmental Panel on Climate Change report released in August 2021.

Katrina in particular became a symbol of dysfunction and failing infrastructure—and raised awareness for the need to adapt to a new climate reality.

Nearly 20 years later, scientists still debate how climate affects hurricanes but they know a lot more, as they get better at the science of what they call “event attribution,” or the linking the causality of individual weather events to climate change.

As NASA puts it, “Earth’s atmosphere and oceans have warmed significantly in recent decades. A warming ocean creates a perfect cauldron for brewing tempests” because “hurricanes are fueled by heat in the top layers of the ocean.”

In the last quarter century, NASA has tracked the largest stretch of high energy hurricanes on record. “So while there aren’t necessarily more Atlantic hurricanes than before, those that form appear to be getting stronger, with more Category 4 and 5 events,” according to NASA.

In 2020, researchers from the National Atmospheric and Oceanic Administration (NOAA) and the University of Wisconsin found an 8 percent per decade increase in the odds that any tropical cyclone globally could become a Category 3 or higher, or those with wind speeds of 111 miles per hour or more. The study encompassed 39 years of storms.

That’s not all.

Oceans warm earlier, allowing storms to form before the official season begins, as happened in 2020’s record setting hurricane season with Tropical Storms Arthur and Bertha in May.

Hurricanes are intensifying faster and dropping more rain. Because of global warming, their destructive power persists longer after reaching land, increasing risks to communities farther inland that may be unprepared for devastating winds and flooding, according to research published in 2020 in the the journal Nature.

With rising sea levels, cyclones also push tidal waters further inland, making storm surges more dangerous and deadly.

With hurricanes being among the costliest of disasters, accounting for a record seven of 22 weather or climate disasters in 2020 that resulted in at least $1 billion in damages, humanitarian agencies are concerned.

There is a “general realization that we are facing a more challenging reality,” Maarten van Aalst, director of the International Red Cross and Red Crescent Climate Centre, which connects climate science with emergency response, told Inside Climate News. 

—James Bruggers and Bob Berwyn

Scientists have long been very confident that the accelerating long-term increase of Earth’s average temperature is also causing spikes in regional daily and weekly high temperatures. For example, if it’s 95 degrees outside and you turn on the heater in your house, it will get much hotter than normal. Just in the last five years, research has shown that human-caused warming greatly increased the likelihood of many recent deadly heat waves, including in late June 2021 in the Pacific Northwest, in Siberia in 2020 and across much of Europe in 2003.

Scientists have also documented a big increase in marine heat waves, which have killed fish, birds, marine mammals, starfish and crabs along the West Coast, shifted fishing grounds in the waters off New England and promoted the growth of potentially toxic algae like red tide in Florida. Research shows how global warming causes such ocean heat waves, which can also fuel extra-strong tropical storms and up the wildfire danger in California. 

Global warming can also intensify heat waves by sucking the moisture out of the ground in the spring, and scientists also have shown that ocean heat waves and heat waves over land are linked. Extreme heat that spills from land over the sea damages coastal ecosystems, and that heat waves and droughts that start over the ocean and then move over land are often the most intense of all. 

—Bob Berwyn

Flooding has existed for millennia. What’s different now is a global population of more than 7.8 billion people, most living in a built environment that can make flooding worse, and forces of climate change that are increasing the risks from flooding.

There are different kinds of floods. Rivers can swell and overflow their banks, inundating whatever is located in a flood plain. Hurricanes and tropical storms can push coastal waters inland, the surge swallowing homes and businesses. Torrential downpours in cities, with their vast areas of hard surfaces like roads, parking lots and rooftops, can overwhelm stormwater management systems, prompting a need for water rescues. Dams can break.

Scientists say climate change can affect all these kinds of flooding disasters, raising risks and costing lives.

Take coastal flooding. The Fourth National Climate Assessment in 2018 by the U.S. government found that global average sea level has risen by about 8 inches since 1900, with almost half since 1993. As sea level rises, so does the prevalence of sunny day flooding, powered by the tides. In July 2021, the National Oceanic and Atmospheric Administration reported high-tide or sunny day flooding had doubled over 20 years, setting records, and was expected to be common along mosts American coasts by 2030

Rising seas also mean hurricanes or tropical storms can push a higher wall of water into inhabited coastal areas, making storm surge more deadly. The climate assessment predicted that sea levels would continue to rise by at least several inches in the next 15 years and by one to four feet by 2100.

Climate change has also energized extreme weather, providing a new awareness of terms like “rain bombs” and “atmospheric rivers.” While flooding can have effects across the economic spectrum, a National Academies of Sciences, Engineering and Medicine report on urban flooding from 2019 found that “poor, racial and ethnic minorities, the elderly, renters, non-native English speakers, and those with mobility challenges were disproportionately affected.”

According to the National Oceanic and Atmospheric Administration, a 1 degree Fahrenheit rise in temperature equals as much as a 4 percent increase in atmospheric water vapor. And an atmosphere with more water vapor can make more precipitation, says Deke Arndt, a top scientist with NOAA. “The biggest events are getting bigger, and big rain is taking up more of our annual rainfall budget,” Arndt notes.

The experts say it’s only going to get worse, as more people move to risky coastal areas, crowd into floodplains and rely on stormwater management systems that were not built with climate change in mind. “Heavy rainfall is increasing in intensity and frequency across the United States and globally and is expected to continue to increase,” the climate assessment concluded. 

— James Bruggers

In the midst of the Anthropocene, human activities—especially human-caused climate change—"have touched every part of the Earth,” Dr. Patrick Gonzalez, a forest ecologist and climate change scientist at the University of California, Berkeley, said. “Nevertheless, we have large expanses of wilderness that still remain relatively unaffected by direct human action.”

The wilderness areas that we do have play a critical role in sequestering carbon. The carbon stored in terrestrial ecosystems, in both vegetation and soil, "amounts to three times the amount of carbon that's in coal and other fossil fuels in the ground,” Gonzalez said.

“The tropical rainforests of the Amazon, the Congo and Southeast Asia contain the largest above ground carbon stocks in the world,” he said. The largest below ground carbon stocks are in the Arctic permafrost.

Scientific field research has shown that primary forests, sometimes called old growth or natural forests, store more carbon than secondary forests, like those that grow after an area is clear cut or burned by wildfire. Not only do primary forests have older, bigger trees, they also have multiple canopies, whereas secondary forests “are usually the same age, and they generally don't have multiple stories,” Gonzalez said.

Another factor: Even as new trees grow, “it takes time to develop the relationships among the plant, animal and microbial species that maintain forest health,” he said.

Once a forest is cleared, it takes at least 100 years for it to fully recover. Some forests, like Coast Redwoods in California—the most carbon-dense ecosystem on the planet—can take centuries to reconstitute.

Primary forests also have higher biodiversity and serve as critical habitat—an especially important function right now, because under the highest emissions scenario, “climate change threatens to increase extinctions of plants and animals up to five times historical rates,” Gonzalez said. 

—Julia Kane 

There are a few things climate change could do, and are already likely doing to California’s majestic and massive sequoia trees, said Nathan Stephenson, a research ecologist with the United States Geological Survey who specializes in how climate change is affecting the nation’s forests.

The “most obvious” impact is an increased threat from wildfires, Stephenson said, as climate change creates conditions that make the blazes more frequent and intense—as seen in the record breaking fires in the summer and fall of 2020.

Fires can destroy the groves where giant sequoias grow and damage and even kill fully grown sequoias, some of which have been alive for thousands of years, Stephenson said. “In the last 10 years, 30 percent of the natural grove area for giant sequoias burned in wildfires,” he said. “That’s more than in the entire preceding century.”

That fact is particularly notable considering just how tough giant sequoias are, Stephenson said—not just in terms of being resilient to fire, but in resisting all harmful conditions to forests such as disease, parasites and drought.

In fact, during a particularly bad California drought from 2012 to 2016, hundreds of giant sequoia died due to a variety of factors, including disease, foliage loss and damage due to bark beetles—parasitic insects that feed on the wood of trees. But the loss of sequoia was minimal when compared to the overall damage California forests faced in that drought. More than 100 million trees died during that time, Stephenson said, a testament to the strength of sequoias.

“Lots of pines died, lots of firs died. Even the hardy infant cedar was dying,” he said. “The tree that died the least was giant sequoia, so there is good news there. They are really tough.”

Still, if global warming continues on its current path, Stephenson said, it’s possible that even the mighty sequoia could see significant damage to its populations in California and around the world. How humans move forward with conservation efforts and how successful they are in reducing greenhouse gas emissions over the coming decades could determine where sequoia can grow and in what quantity, he said.

If anything, Stephenson said, seeing the kind of stress sequoias face today should warn us that climate change has already pushed many tree species to their limits. “Sequoias really may not be the canary in the coal mine because they are so much more resilient than the surrounding tree species,” he said. “It’s almost like the sequoias are finally starting to feel the effects.” 

—Kristoffer Tigue

Scott Stark, a researcher with the Tropical Forest Ecology Laboratory at Michigan State University, said that’s one of the most important scientific questions of our time. It needs a good answer because the Amazon stores a lot of carbon that would otherwise end up in the atmosphere as carbon dioxide, warming the planet. 

“The Amazon also helps cool the Earth by maintaining a cloudy wet atmosphere over the South American continent,” Stark said.

University of Arizona ecologist Scott Saleska said a recent research paper helps answer the question, suggesting that deforestation of from 20 to 40 percent of the Amazon could push the ecosystem over the brink toward permanent aridification.

“This is not something that is out there in the future. It is already happening now, and it will get worse with more climate change and deforestation,” Saleska said. “We may be at or approaching the threshold already and we don’t want to do this experiment to find out for sure!” The threshold, he said, depends not just on deforestation but on the degree of climate change. 

“Warming brings us closer to a tipping point all by itself,” he said. “The more warming we have the less deforestation is needed, and vice versa.”

The NASA Earth Observatory maintains detailed information of Amazon deforestation, including links to new research. 

—Bob Berwyn

Activists have multiple reasons for trying to stop new fossil fuel pipelines from being built. For one thing, pipelines can and do leak. In 2010, Enbridge’s Line 6B pipeline broke in Michigan, spilling more than 1 million gallons of diluted bitumen into a tributary of the Kalamazoo River. About 150 families had to move as a result, and the clean-up cost more than $1 billion. While this incident was especially bad, dozens of other serious pipeline incidents resulting in injuries and deaths are reported each year in the United States. The Kalamazoo River spill galvanized ranchers and other landowners to oppose the Keystone XL pipeline, which was first proposed in 2008 and meant to transport the same type of oil between the Alberta tar sands in Canada and the Gulf Coast of Texas. President Joe Biden canceled the pipeline’s permit on his first day in office and the project was canceled.

Often, pipelines cut across or pass very near land belonging to First Nations and Native American tribes. The Dakota Access pipeline transports crude oil under the Missouri River less than a mile from the Standing Rock Sioux reservation, which relies on the river for drinking water. Construction of the pipeline also damaged important cultural sites and artifacts. Thousands of Indigenous people from dozens of tribes, as well as supporters from around the world, eventually gathered at Standing Rock to protest the pipeline. Now, activists are trying to stop Enbridge’s new Line 3 pipeline, which would cross hundreds of streams and wetlands in Minnesota, including the wild rice habitat that’s central to Anishinaabe culture. Protestors argue that the planned pipeline imperils the Ojibwe people’s treaty rights to hunt, fish and gather on their ancestral land and waterways.

In addition, activists oppose these pipelines simply because building new fossil fuel infrastructure slows down the transition to clean energy (although people disagree over what, exactly, counts as clean energy). “This pipeline isn’t just about this place or the Anishinaabe or the wild rice,” protestor Joe Hill, who’s a member of the Seneca Nation, previously told Inside Climate News. “It’s about the world and what will happen if we don’t shut the tar sands down.”

Many experts do agree that to reach the Paris accord goal of limiting global warming to 1.5 degrees Celsius, the world needs to reach net zero greenhouse gas emissions by 2050. Recently, the International Energy Agency—historically a conservative organization—concluded that for this to be possible, new oil and gas development must stop immediately. 

—Delger Erdenesanaa

Essentially, municipal governments want the fossil fuel companies to pay for the costs of dealing with climate change. Taxpayers can't pay the bill to mitigate climate-related disasters such as coastal and inland flooding; hurricanes, droughts, heat waves and wildfires. The companies are accountable for a substantial portion of those climate crisis-related impacts, because they are responsible for an increase in CO2 emissions; the greenhouse gas responsible for global warming. Consequently, the local governments believe they should pick up the cost of protecting public and private property.

—David Hasemeyer

State prosecutors have alleged Exxon and other oil companies knew for nearly 50 years that production and burning of their fossil fuels created greenhouse gas emissions that warm the planet and cause climate change. Yet the companies nevertheless engaged in a coordinated effort to conceal and downplay those risks by denying their own knowledge of the threats, attempting to discredit scientific evidence and creating doubt in the minds of the public. While masking the consequences, the industry increased its production of fossil fuels, causing, in turn, a significant increase in global greenhouse gas emissions. 

—David Hasemeyer

David Lyon, a scientist with the Environmental Defense Fund, said “it’s a great question, but it’s always going to be specific to situations.” And, he said, you need to know a lot of details to get an answer.

Lyon and his colleagues have spent years researching the different pieces of this question. While there are many factors to consider, including the efficiency of the power plants in question, one of the most important is how much methane is leaking from wells, valves, pipelines and other equipment that carries the gas to power plants. Natural gas is composed primarily of methane, which is itself a greenhouse gas that traps much more heat per pound than carbon dioxide. So while a natural gas-burning power plant emits less carbon dioxide—or CO2—than a coal plant, those savings can be offset by any methane that leaks on its way to the plant.

“If it’s greater than a 2.7 percent loss rate,” Lyon said, “then there will be a period of time during which the climate impacts due to the methane emissions cause more damage than the benefits of having less CO2 from combustion. So I guess the question is what’s the leak rate of gas that we’re using in the United States?” he said. “What we found is that at least nationwide it’s pretty close.”

Nationally, the rate may be slightly below that 2.7 percent threshold, Lyon said, but there’s a lot of variation depending on where the gas is coming from. In the Permian Basin, which stretches across parts of Texas and New Mexico and is the nation’s most productive oil and gas region, Lyon and colleagues found that about 3.7 percent of all the methane produced leaks into the atmosphere. That means a new gas plant using Permian Basin gas would likely have a worse impact on the climate than any coal plant it replaced, at least in the short term. In parts of Pennsylvania’s Marcellus Basin, however, the leak rate is below 1 percent.

Lyon’s answer points to another complicating factor: while methane is a more potent greenhouse gas than CO2, it breaks down much more quickly. So switching from coal to gas could be worse for the climate when examined over a 20-year time frame, for example, but better over the course of a century. Some science and policy experts say that the urgency of limiting warming over the next few decades means continuing to invest in new natural gas power plants carries great risks.

Perhaps most important, however, is the fact that renewable sources such as wind and solar are available, and are in many places competitive with or even cheaper than new natural gas plants. Lyon said it is often politics, rather than technical feasibility, that stands in the way of switching directly to renewables. And while gas can be better than coal under the right circumstances, he said, “it’s never going to be as good as renewables.” 

—Nicholas Kusnetz

According to the Paris Agreement, global temperature rise over pre-industrial times needs to stay well below 2 degrees Celsius (3.6 degrees Fahrenheit), preferably 1.5 degrees Celsius (2.7 degrees Fahrenheit). (In 2017, warming reached 1.8 degrees Fahrenheit over pre-industrial times.) If nations fail to act, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) warns, runaway climate change will expose hundreds of millions of people to extreme climate events, including heatwaves, droughts, severe flooding and tropical cyclones.

The Paris Agreement, signed by nearly 200 countries, seeks to limit warming as much as possible by aiming for the more ambitious goal of 2.7 degrees Fahrenheit. This would require global greenhouse gas emissions to be cut in half by 2030 and then to zero by mid-century. But the longer nations wait, the more drastic cuts to emissions are needed.

Right now the globe is on a trajectory to reach between 4.5 and 4.9 degrees Fahrenheit (2.5 to 2.7 degrees Celsius) of warming by 2100. Scientists predict that when we reach somewhere between 2.7 and 3.6 degrees Fahrenheit (1.5 degrees and 2 degrees Celsius) of warming sometime around mid-century, the Arctic shelf will enter a feedback loop of melting. In this scenario, sea levels would continue to rise for thousands of years.

But there is some hope. Climate scientists had previously thought that many decades, or even centuries, of warming were guaranteed even after greenhouse gas emissions stopped. But they now believe that warming would stop within a couple of decades. 

—Agya K. Aning

It means we have just a few years to make significant cuts in greenhouse gas emissions, the primary cause of global warming. It’s not an end-of-the-world date. The genesis of the 12-year number was a 2018 report by the United Nations Intergovernmental Panel on Climate Change that drew a line in the sand. The message then was that within 12 years, the world must be on a path to net zero CO2 emissions by mid-century. Meeting that goal means keeping global warming to a maximum of 1.5 centigrade. Anything above that will greatly increase the risks of sea level rise, drought, floods, and extreme heat.

—David Hasemeyer

The planet’s average temperature is now 1.2 degrees Celsius warmer than it was before the industrial revolution in the late 1800s, according to the World Meteorological Organization. We are already seeing more intense heat waves, storms and other consequences. The goal of the international Paris climate accord is to prevent much worse, by limiting global warming to “well below” 2 degrees Celsius and ideally to 1.5 degrees Celsius.

In 2018, climate scientists convened by the United Nations published a report warning us of what is likely to happen beyond 1.5 degrees Celsius of warming. At 1.5 degrees warming, sea level is expected to rise by 10 to 30 inches (26 to 77 centimeters), putting 10 million more people at risk from coastal storms and flooding. Heat waves will continue to get worse, exposing 14 percent of the world population to extreme heat at least once every five years. Ecosystems will suffer, too. After 1.5 degrees Celsius of warming, up to 90 percent of all coral reefs could die out, and about 7 percent of Earth’s land area could shift into a new biome, with grasslands turning to desert, tundra turning to forest, etc.

At 2 degrees Celsius, some of these climate impacts will become twice as bad as they would be at 1.5 degrees. But these numbers shouldn’t be viewed as sudden cliffs. “Every half-degree matters,” Penn State University climate scientist Michael Mann told Inside Climate News in 2018. “A better analogy is a minefield. The further out on to that minefield we go, the more explosions we are likely to set off.”

After early heat waves across the northern hemisphere in the summer of 2021, some scientists think we are already setting off more explosions than expected. They warn that even 1.5 degrees Celsius may not be as safe, relatively speaking, as previously thought, and urge communities to start preparing and adapting. 

— Delger Erdenesanaa

This is one of the most common questions asked of Katharine Hayhoe, an atmospheric scientist at Texas Tech University and one of the country’s leading climate science communicators.

“The answer is yes and no, and the analogy I use is this: It’s as if we’ve been smoking a pack of cigarettes a day for years and even decades, so some lung damage is already here today,” she said. “But we don’t have emphysema, we don’t have lung cancer and we’re not dead. So that means that it’s not too late to avoid the worst impacts. And when is the best time to stop smoking? As soon as possible, as much as possible.”

Hayhoe said the question has its roots in both a misunderstanding of climate science and, perhaps more importantly, in human psychology. In regards to the science, the concept of thresholds—1.5 degrees Celsius (2.7 degrees Fahrenheit) as a limit to global warming, for example—has unfortunately led some people to think that acting isn’t worth it if the goal can’t be reached.

In fact, while some level of dangerous warming is already baked into the climate system, efforts to limit emissions can still prevent those changes from becoming much worse. She pointed to a major report released by the Intergovernmental Panel on Climate Change in 2018. Many people misinterpreted one of its findings and concluded that the world had only 12 years to cut emissions by 45 percent.

“What the IPCC report actually said,” she said, was that “every action matters, every choice matters, every year matters. That’s the key result of that report. Somehow that got changed into: ‘We have 12 years.’”

But Hayhoe said many people who believe that it’s “too late” are driven less by misunderstanding the science than by despair.

“I think a lot of the doomerism comes from people who have been burned out, who feel like they’ve been worried and anxious for so long and nothing has changed, so that means nothing ever will,” she said. “And that breaks my heart.”

Hayhoe said this anxiety-fueled desperation can create a self-fulfilling prophecy, where people become locked into inaction, thereby making change impossible. Yet if people can will themselves into action, she said, they may begin to feel more hope. A similar logic applies to voting, she said. People sometimes opt out of elections because they think their vote doesn’t make a difference. Yet the simple act of voting, she said, can make people feel more empowered.

“Scientifically speaking, it is absolutely not too late to avoid the worst of the impacts,” Hayhoe said. “But if we decide that it is, then it will be.”

— Nicholas Kusnetz

COP26 is the latest in a series of annual global climate negotiations under the umbrella of the United Nations Framework Convention on Climate Change (UNFCCC). The 2021 Conference of Parties is from Oct, 31 to Nov. 12 in Glasgow, Scotland, and is being held after a one-year delay due to the Covid-19 pandemic.

The UN climate framework was launched in 1992 and 196 countries, plus the European Union, are parties to the global climate treaty. Notable steps in the COP process include the 1997 Kyoto Protocol, the negotiation stalemate in Copenhagen in 2007 and the 2015 Paris Climate Agreement.

The goal of the UNFCCC process, including COP26, is to stabilize greenhouse gas concentrations in the atmosphere at a level that will “prevent dangerous human interference with the climate system, in a time frame which allows ecosystems to adapt naturally and enables sustainable development.”

Under the Paris agreement, 196 countries agreed to try and limit global warming to less than 2 degrees Celsius, compared to average temperature in the industrial era from 1850-1900. Since 2015, the annual COP meetings have been mainly focused on implementing the mechanisms of the agreement to make that happen, including voluntary national pledges to reduce greenhouse gas emissions, international monitoring and verification of those efforts.

The initial round of pledges add up to annual emissions reductions of about 8 gigatons per year, and since then, new pledges have increased that to about 11 gigatons per year—still not nearly enough to reach the goal, which would require cuts of about 40 gigatons per year over the next decade, according to Sivan Kartha, a climate policy expert with the Stockholm Environment Institute.

Other key elements that will be negotiated at COP26 in Glasgow include increased climate financing from developed countries whose emissions have caused most of the warming to less developed countries that are most vulnerable to harmful climate impact, and working toward a global price on carbon that could help drive cuts in greenhouse gas emissions.

Some have called COP26 the "last chance" for climate action, but Kartha said the meetings should be seen not as a last chance but as the next step in an evolving process.

“It’s not the last chance, because that last chance happened quite a long time ago,” he said. “Dangerous climate change is already here. At COP 26, we need to do everything we can to really seriously tackle the problem. The biggest thing from the bird’s eye view, is that Glasgow marks the outcome of the first round reviewing what countries put on the table in Paris, deciding how we are doing and then responding with increased more ambitious efforts.”

— Bob Berwyn

Nobody has stated that the ice age has ended. Twila Moon, a climate scientist with the National Snow and Ice Data Center, said, “We are still within an ice age. We do have large ice sheets on Earth, but we are in an interglacial, as we have less ice and are losing it. Hothouse Earth is the phrase commonly used to describe periods when there is no ice on Earth and the Arctic might be green and warm,” she said.

She added, “Because of human-caused climate change, we run the risk of quickly moving the Earth into a hothouse state. This would not be good for humans or the other living things we depend on, especially since we are making this change happen quickly right now.”

Moon noted that before humans started changing the climate so rapidly, other geologic and planetary processes created the changes.

“For example, the Earth changes its orientation and orbit—these ’slow’ (in human metrics) changes shift the amount of sun the Earth receives and that can allow ice sheets to grow or to diminish,” she said.

More detailed information is available at this website. 

— Bob Berwyn

Working now to prepare for future mass migrations would require a shift in both public policy and perception, said Kristina Shull, a public history and interdisciplinary scholar specializing in race, foreign relations, immigrant control and prison privatization, who recently joined the history department at the University of North Carolina, Charlotte. Shull noted that mass migrations are already underway because of the effects of climate change, both through direct displacement by major natural disasters and slower onset, often less visible phenomena like sea level rise and drought, which can lead to crop failures and, in turn, economic and political strife. 

“The public doesn’t always make those connections to see that these migrations are happening now,” said Shull, “but they definitely are likely to increase.” Estimates of the number of climate migrants range from 25 million to 1 billion by 2050. 

“We have options of how to see and understand migrations, and also how to respond,” said Shull. But, she warned, the current global response to mass migration seems to be going in the wrong direction. For instance, today there are over five times as many border walls as there were when the Berlin Wall fell in 1989. In Shull’s mind, this increasingly securitized and militaristic response to migration only “exacerbates the problem,” and is not only “unsustainable” but also “deadly” and “misinformed.” 

As a historian, Shull argued for a “historical approach” to the issue of climate-induced mass migration, by which she said she means an approach that is “humanistic” and understands the societal structures that have historically shaped migration patterns, so that one can “see migration as a natural and logical response” to global inequality and injustices, and “have a clear understanding of who is responsible” for them. With that in mind, she said, “we can better advocate for solutions and move towards repair and balance.” For Shull, that advocacy includes recognizing migration as a basic “human right,” both one “to move” and “to stay,” as well as to see migration “not as a threat, but as an opportunity for justice.” 

—Ilana Cohen

Managed retreat is the process of moving people and infrastructure away from places that are too exposed to environmental hazards. People often use the term in the context of climate change and sea level rise, but managed retreat can also happen in areas prone to wildfires, earthquakes or other natural disasters.

In the United States, managed retreat usually involves the government buying the homes of people who live in risky places and want to move. After a buyout, the government will remove or demolish empty homes to prevent others from moving in and facing the same risks. Sometimes the areas people have retreated from will become restored natural habitats like wetlands, which help buffer nearby towns and cities from storms and floods. 

Managed retreat is often seen as an option of last resort. But retreat isn’t necessarily worse than other ways of adapting to climate change, like building sea walls. “None of these adaptation options are going to be the right answer everywhere,” said A. R. Siders, a professor at the University of Delaware’s Disaster Research Center, who specializes in adaptation to climate change. “It's about figuring out which one best fits this particular context.”

Managed retreat is already happening in Hawaii, New York, Louisiana and other coastal regions, not just with people’s homes, but with roads and other infrastructure. And increasingly, entire communities are banding together to advocate for their collective managed retreat. But not everyone who wants to move can. Most funding for managed retreat in the United States depends on officials declaring a disaster, explained Liz Koslov, a professor of urban planning at UCLA. For years, Indigenous villages in Alaska have asked for help moving their communities in response to gradual coastal erosion, but haven’t gotten funding. On the other hand, after Hurricane Sandy hit New York, many residents of Staten Island were able to sell their homes to the government and move. (But even there, demand exceeded the actual number of buyouts). 

—Delger Erdenesanaa

Some environmental groups do address population, though often in nuanced and muted ways. The subject can quickly become controversial, with environmentalists arguing it is not how many people are on the planet, but what resources they consume.

For example, Wendy Becktold wrote in 2019 in Sierra, the magazine of The Sierra Club, that the annual carbon footprint of the average U.S. resident—assuming they drive a car, heat their home with coal or natural gas and eat meat and hop an airplane for vacations is as much as 15 times greater than a Ugandan farmer.

But the underpinnings of the population vs. resources argument are changing, with billions of people rapidly moving into the global middle class, consuming more resources as they do. As a consequence, environmental groups and the public need to think in new ways about the issue, said Eileen Crist, a Virginia Tech associate professor emerita in the Department of Science, Technology and Society, and co-editor of the 2012 book, “Life on the Brink: Environmentalists Confront Overpopulation.”

All told, there were about 7.8 billion people as of mid-2021. World population has been growing at a rate of between 1 percent and 2 percent a year since 1950, but for the first time in modern history, global population is expected to all-but-stop at about 10.9 billion by 2100, because of declining fertility rates, according to a 2019 Pew Research Center analysis of United Nations data.

Still, that’s a lot of people—enough to concern nearly 14,000 scientists who have as of mid-2021 signed a call for urgent global action on climate change and included population among several challenges that must be met if the world is to successfully confront climate upheaval. Population should be stabilized and slowly reduced in ways that ensure social integrity and protect human rights, wrote Oregon State University forestry professors William Ripple, Christopher Wolf and two other scientists in the journal BioScience, under the headline “World Scientists’ Warning of a Climate Emergency.”

Crist is one of the signatories from 158 countries to the BioScience article. In a memo to Inside Climate News, Crist wrote that renewable energy systems of the scale needed to replace fossil fuels, in a world where the global middle class is burgeoning and consuming more energy, “will require vast metal and mineral resources, infrastructure build-out, and land and sea area for solar and wind farms. These requirements entail more ecological destruction, pollution, and natural habitat constriction. Moving intentionally toward decreasing our numbers will help downscale the material-technological demands of a renewable-energy economy, while preserving Earth’s remaining biological heritage.”

Crist also observed that the world is “on course to surpass the 1.5-degree Celsius warming that climate scientists hope is a safe boundary.” But even under best-case scenarios, Earth and its inhabitants will face worsening droughts, floods, heatwaves, storms, sea-level rise and mega wildfires. 

“These catastrophes will pummel and displace tens, if not hundreds, of millions of people,” she wrote. “With this specter at our doorstep taking proactive steps to address the population factor … is the starkly rational course.”  

—James Bruggers

America has a long history of government and industry placing environmental hazards, such as landfills, refineries and incinerators, in minority and low-income communities. Even to this day, the people who live in such places are often given no say in what types of facilities are placed in their neighborhoods. Environmental justice is the response to such conditions—it is the communal pursuit of environmental self-determination.

Since the 1980s, numerous studies have shown that the variable most predictive of who lives near environmental hazards is race, even when accounting for other factors like geography and socioeconomic status. Activists define the actions that create such conditions, whether they are intentional or not, as environmental racism.

The movement’s basic demands are that minority communities should not have to disproportionately shoulder the burdens of environmental hazards and should be able to enjoy the same benefits of environmental law enforcement, clean energy and the mitigation of climate disasters, like floods, droughts and fires.

To achieve their goals, activists seek involvement in the permitting and siting of facilities, and redress whenever harm befalls a community. In taking these actions, they have expanded the definition of the environment. Whereas it was previously associated with conservation and preservation, the environment now relates to all places that humans inhabit, like workplaces, schools and homes. 

— Agya Aning

Daniel Kammen, a professor of energy at the University of California, Berkeley, said nuclear power “is at this incredibly exciting point, and I say that as a professor of nuclear engineering.”

Kammen said a wave of investment from the public and private sectors has led to unprecedented innovation in recent years, focusing on so-called “modular” reactors that are much smaller than conventional nuclear plants.

These smaller reactors could theoretically be scaled up or down to meet different needs. But Kammen said it is too soon to say whether they will overcome one of the biggest hurdles facing nuclear power plants: they are very expensive to build. The first test reactor is still several years away from operation, and no matter its success, modular reactors will need to compete with wind and solar power paired with energy storage, the costs of which are falling rapidly.

Kammen said scientists also have not solved how to handle the radioactive waste produced by the reactors. The waste issue has bedeviled nuclear power plants, with no clear solution for how to dispose of or store the materials long term.

“There’s a real renewed interest, certainly, thinking about how renewable energy and nuclear power can be seen as partners in the low-carbon economy,” Kammen said. “There’s very exciting opportunities here, but again this waste and cost and risk question is still unresolved.” 

—Nicholas Kusnetz

Who better to explain the Keeling Curve than Ralph Keeling.  It was research by his father, Charles David Keeling, beginning in 1958 at the Mauna Loa Observatory in Hawaii, that continues to provide some of the most convincing scientific evidence of increasing amounts of atmospheric carbon dioxide, the primary driver of global warming.

The Keeling Curve bridges present day concentrations of atmospheric CO2 with those of the past by making daily observations that show the potent greenhouse gas is accumulating in the atmosphere.

Keeling, a professor of climate sciences at the University of California at San Diego, described the curve first plotted by his father as an “iconic record that embraces the depth of the climate problem” triggered by burning fossil fuels.

It may be a plain-looking chart, but seeing the line go up and up and up is significant because it represents more heat being trapped by the atmosphere that in turn is causing the planet to become warmer than it would be naturally.

“It is the most compelling evidence of human impact on the planet,” said Keeling, who continues his father’s work at UCSD’s Scripps Institution of Oceanography.

Keeling said he is optimistic that a total climate disaster can be avoided but that it will require a massive reduction in carbon emissions to bend the Keeling Curve in the opposite direction.

He calls his father prescient for the work that is led to the Keeling Curve.

“He saw the inevitability,” Keeling said. “His science was aimed for the future that is not only today but tomorrow.”

And is he proud of his father? “Yes.”

—David Hasemyer

Cities tend to be hotter than surrounding suburban or rural areas, creating “heat islands.” This happens because cities have less trees and vegetation, which cool the air, and more buildings and roads, which usually heat the air. The temperature inside a city is generally 1-7°F hotter than outside the city, according to the Environmental Protection Agency.

Individual neighborhoods can get even hotter. Areas that were subject to racist housing policies in the past, like Brooklyn’s Brownsville neighborhood, have less vegetation and more built surfaces, and are hotter today than other parts of their cities. These formerly redlined neighborhoods are still home mostly to low-income communities of color, where many households can’t afford air conditioning.

In extreme cases, the urban heat island effect can turn deadly. Cities have a higher baseline temperature to start with, so during heat waves they get especially hot. Over the past 30 years in the United States, extreme heat has killed more people than any other kind of weather. Along with those who lack air conditioning, people who work outside (like construction workers) are especially at risk. Even if it doesn’t kill, too much heat can exacerbate pre-existing illnesses or make people sick through dehydration and heat stroke.

Cities like Louisville, Kentucky are trying to shrink the urban heat island effect by planting more trees and subsidizing more reflective roofs or green roofs on buildings. These physical interventions help, but they aren’t the only things cities can do to protect their residents, said Juan Declet-Barreto, a social scientist who studies environmental hazards at the Union of Concerned Scientists. For example, city governments can also help residents weatherize their homes or pay for air conditioning. They can offer public cooling centers, and prevent people from being evicted or losing their utilities during the hottest parts of the year.

And of course, cities are suffering from more extreme heat as climate change goes on. “There's only so much that we can do to adapt,” said Declet-Barreto. To prevent climate change from cranking the urban heat island effect to a broil, he said we also need rapid reductions in greenhouse gas emissions.  

—Delger Erdenesanaa

Climate variations are not unusual. The Earth has swung between ice ages and warm periods for hundreds of thousands of years. But the rate and the extent of current warming go beyond anything in recent geologic time. The overwhelming consensus of scientists is that changes in climate since the start of the industrial revolution 150 years ago cannot be attributable to natural causes. Industrial civilization—driven by burning fossil fuels—then becomes the common denominator. Burning coal, oil and gas releases heat-trapping carbon dioxide. Precise scientific measurements reveal CO2 levels in the atmosphere have been steadily climbing as more of these fuels are burned. When fossil fuels are burned, they release CO2 and other greenhouse gases that trap heat in the atmosphere, making them the primary contributors to global warming and climate change. 

—David Hasemeyer

Solar radiation from the sun passes through the Earth’s atmosphere largely in the form of visible light. That sunlight heats the Earth, and much of that heat radiates back out towards space in the form of thermal energy. Unlike visible light waves, which pass through the atmosphere largely undisturbed, much of the thermal energy radiating back toward space is absorbed by the Earth’s atmosphere.

This trapping of thermal radiation or heat in the Earth’s atmosphere is called the greenhouse effect. The greenhouse effect makes Earth habitable for humans. If Earth’s atmosphere didn’t trap heat, the planet would be much colder—too cold to sustain human life. Water vapor in the Earth’s atmosphere is a leading cause of the greenhouse effect. “Greenhouse gases,” pollutants including carbon dioxide and methane, trap additional heat.  The more these gases build up in the Earth’s atmosphere, the hotter it gets.

“The natural greenhouse effect is vital to supporting life on Earth but like anything, too much of a good thing causes problems,” said Drew Shindell, an earth science professor at Duke University. 

— Phil McKenna

Scientists with NASA measure the changing climate through a set of vital signs, similar to the way doctors monitor a patient in a hospital. Those data, compiled from millions of global measurements per year, clearly show that fossil fuel burning has given Earth a long-running fever. 

The concentration of carbon dioxide in the atmosphere has increased by about 50 percent since 1880, raising the average global surface temperature by 2.2 degrees Fahrenheit since then. Based on studying air bubbles trapped in ancient ice and other fossil records, several studies estimate the CO2 level hasn’t been this high since the Pliocene era, from 5.3 million to 2.6 million years ago, when the average global temperature was about 5.4 degrees Fahrenheit warmer than today.

NASA’s vital signs also show that Arctic sea ice has declined 13.1 percent per decade since 1979, shifting the region toward an “unprecedented state,” scientists said in a key 2019 report. Polar ice sheets, as well as mountain glaciers are melting quickly and sea level is rising about 1 inch every eight years, and not just because of the melting ice—the world’s oceans have absorbed about 93 percent of the heat trapped by greenhouse gases, and that warming expands the water, bulging it shoreward. 

Researchers also have calculated that all the planetary warming since the late 1800s has been caused by human activity, mainly fossil fuel burning, but also by changes to land areas from logging, farming and urban development. Without the human-caused changes, Earth would have cooled slightly since then based on factors like volcanic eruptions and slight changes in the planet’s orbit. 

— Bob Berwyn

Jennifer Jurado, chief resilience officer for Broward County, Florida, said global average sea level has risen between 6 and 8 inches since 1880, with regional variations.

“In Southeast Florida, the amount of measured rise is closer to 9 inches, with 3 inches just since 1992,” she said. “Perhaps small rates of rise don’t produce dramatic effects for communities at higher elevations, but many coastal areas are flat and low-lying (sitting just a foot above sea level, or less) so that even gradual changes over time have pronounced effects and can result in significant inland movement of tidal water.”

Existing drainage systems and seawalls are already being swamped by tides that are 12 inches higher now than they were when the structures were designed and built 50 years ago, she said.

She added, “Without higher seawalls and redesigned stormwater systems, the flooding will become permanent. In our region, the impacts have become so severe, there is no longer debate about the need to upgrade and to plan for future conditions.” In Southeast Florida, a projected sea level rise of 40 additional inches by 2060 is the basis for planning and designing all new infrastructure.

More information on sea level rise is available in this Q&A with an expert from the National Oceanic and Atmospheric Administration. 

—Bob Berwyn

Coastal flooding as sea level rises with future greenhouse gas emissions will rapidly get worse over the coming decades, according to the National Oceanic and Atmospheric Administration. 

In the past, powerful storms caused coastal flooding. But sea level rise will mean common wind events and high tides will more frequently cause ocean waters to spill into communities. Rising sea levels will make more and more cities progressively vulnerable to high tide flooding, which is rapidly increasing in frequency, depth and extent along many U.S. coastlines.

Rising sea level also will increase the salinity of coastal aquifers and impair water quality for coastal communities around the world, most of which depend on groundwater. Exacerbating matters, many coastal regions will face the double threat of sea level rise and sinking land.  

“One thing that always goes unrecognized is that sea level rise alone is not as dangerous as when it's combined with vertical land motion, or land subsidence,” said Manoochehr Shirzaei, a geophysicist at Virginia Tech who studies the impacts of subsidence and sea level rise on coastal areas.

And that difference between the change in land elevation and the change in the sea surface level, called relative sea level rise, Shirzaei said, “can be really devastating.” 

With sea level rise alone, people living along vulnerable coastal areas could probably elevate their house by a meter and stop worrying. But land can sink rapidly, by four or five centimeters a year in some coastal regions, he explained. 

Under the worst case climate models, where nothing is done to curtail greenhouse gas emissions, sea level is projected to rise about 10 millimeters (0.4 inches) per year by the end of the century, Shirzaei said. In contrast, the rate of land subsidence could approach hundreds of millimeters in some places.

“That’s something that has to be paid attention to, if you care about the risk and hazard associated with sea level rise and flooding,” Shirzaei said. “But unfortunately, it doesn't get as much attention as sea level rise itself.”

By the end of the 21st century, more than 1 billion people will live by the coast, he added. “As sea level rises and the land erodes, we will have less space for these people to live.”

Exactly how these climate impacts will affect people and the economy isn’t known, he said, because scientists haven’t yet figured out how to link socioeconomic and physical models. One thing is clear, though, Shirzaei said: “We have to take measures to reduce carbon emissions and slow down the warming of the climate.”

And those measures have to be coordinated at the international level, he said. “The problem is at a state that is past individual action.”

For more information on sea level rise, and relative sea level rise, see NASA’s Rising Waters. 

—Liza Gross

Developers of solar geoengineering, also known as solar radiation management, propose to combat warming by limiting the amount of sunlight that reaches the Earth and is converted to heat through the greenhouse gas effect.

Many approaches to solar geoengineering have been proposed, ranging from small-scale reflective ‘cool roofs’ to space-based sun shields. But two are garnering serious investigation by researchers, according to a report released earlier this year by the National Academies of Sciences, Engineering, and Medicine. One, ‘stratospheric aerosol injection’, would release small reflective particles, such as calcium carbonate or sulfate, into the stratosphere to scatter the sun’s rays. The second, ‘marine cloud brightening’, would add aerosols—most often proposed are sea salts—to low-level clouds over ocean waters to increase their reflectivity.

The report also said that neither of these techniques is without risks. Large uncertainties loom in how solar geoengineering interacts with atmospheric chemistry, regional and local climate or the potential for ‘termination shock’ if interventions are suddenly stopped. Barely studied are solar geoengineering’s likely domino effects on critical ecosystem functions, such as photosynthesis, said ecologists in a 2021 report in the Proceedings of the National Academies of Science.

Despite the potential downsides to solar geoengineering, both reports acknowledge the increasing urgency to conduct research now, before any measures are hastily put into effect out of climate-driven desperation in the future. Still, scientists stress that solar geoengineering is only being considered as a last resort to avoid crossing disastrous tipping points and prevent irreparable damage to Earth’s inhabitants.

Climate justice researchers and advocates, meanwhile, argue against investing in solar geoengineering research because these strategies neither address the root cause of climate change—greenhouse gas emissions, primarily from fossil fuels—nor stop related changes such as ocean acidification. They also worry that adopting these technologies might exacerbate socioeconomic inequities and weaken commitments by business and governments to cut emissions.  

Solar geoengineering isn’t only a scientific pursuit, but also a political and social decision, said Sikina Jinnah, an associate professor of Environmental Studies at the University of California, Santa Cruz. The current governance structures for regulating this technology, she said, are “sorely inadequate”.

“The social and justice issues, in my view, are just as if not more important than some of the technical questions,” she said. “How do you make decisions about how solar geoengineering might be deployed? Who controls the thermostat?”

—Haley Dunleavy

Carbon capture and storage refers to technologies that pull carbon dioxide out of the exhaust in smokestacks, or directly from the air, and either store the gas underground or convert it into a usable product. The technology has existed for decades in some industrial uses, like processing natural gas. Increasingly, however, many policy experts, scientists and fossil fuel industries say carbon capture and storage could play an important role helping to meet climate goals.

That may be true, technically speaking, said Daniel Kammen, a professor of energy at the University of California, Berkeley, but he is skeptical that the technology will play a significant role, at least within the electric power sector. The challenge, he said, is that carbon capture and storage, or CCS, remains extremely expensive.

Kammen pointed to President Joe Biden’s goal of reaching 100 percent carbon-free power by 2035.  “That means that really no new fossil plants can really be built,” he said, because new power plants last decades. The best opportunity for the technology, then, would be to retrofit existing power plants, “and that’s very unlikely, because CCS is not economically competitive today. It’s very far from it. And early retrying of fossil plants, and being replaced by wind and solar and storage is a far better economic deal.”

Much of the renewed interest in carbon capture in recent years has been focused on other uses. The technology could be used to remove carbon dioxide emissions from sectors without viable carbon-free alternatives, such as cement and steel manufacturing. Many energy companies say CCS could allow them to use natural gas to produce emissions-free hydrogen, which could be used as a fuel for transportation and heavy industry. Increasingly, some companies and researchers are exploring technologies that remove carbon dioxide directly from the air, though the process remains extremely expensive. Advocates have argued that governments need to fund research into carbon capture to help drive down costs, because every tool will be needed to limit global warming.

Kammen said these opportunities could play a role in the energy system, “but as a large scale climate solution I really don’t see it fitting in, because renewables and energy storage have progressed so dramatically that we’re really in a phase of closing out our fossil plants, not finding ways to basically give them life extension, which is effectively what CCS would be.” 

—Nicholas Kusnetz

A big concern that communities have when faced with climate change-related disasters is the displacement of people, said Marissa Ramirez, who works as the project manager for SPARCC, an organization currently working to help six communities prepare for climate change. 

Displacement, Ramirez said, whether it's “temporary or permanent, forced or voluntary is rooted in inequity and exacerbated by climate change.”

Key for resilience and reducing displacement, Ramirez said, is to focus on the needs of the most vulnerable groups, often populations of people of color, who will be most heavily affected by events like floods, fires, hurricanes and heat waves. 

Some solutions, Ramirez said, include increasing affordable housing and community engagement. Resilient communities prioritize long-term affordability. 

The thinking that goes into resilient solutions is complex. Ramirez used the example of air conditioning. As heat waves become longer, hotter and more frequent, people will need access to air conditioners and electricity to power them. Yet consuming electricity currently contributes to greenhouse gas emissions. 

“We need to provide air conditioning now, but we need to think about is that maladaptive for our future, where our climate will continue to change?” she said.

One solution is to start constructing buildings that will stay cooler and designing communities to prepare for future warming.

“We can't keep designing communities for today, because it’s going to be hotter tomorrow, it might be wetter tomorrow, it might be drier,” she said. “The homes that we have right now may not shelter us safely in the future.”

Here’s more from Ramirez on community resilience. 

—Katelyn Weisbrod

Carbon offsets are a reduction in emissions of heat-trapping gases like carbon dioxide or methane made to compensate for emissions generated somewhere else. As far as the atmosphere is concerned, it doesn’t matter where the reduction occurs.

Offset programs can be detailed and opaque, and there are concerns about some of them delivering on their promises. 

“It’s hard to figure out which offsets really are good, and which ones are not that great,” said Alex Hanafi, the lead counsel for Environmental Defense Fund’s global climate program. “It is not an easy choice for consumers, or even well sourced companies.”

Because they are a big part of the global response to climate change, the stakes are huge.

“If these offsets are designed well, if they are created and monitored in a robust way, they can really help the climate,” said Hanafi. “If they are not, they won’t.”

There are mandatory and voluntary carbon offset programs designed to deal with everything from large scale industrial emissions that are regulated as part of a cap-and-trade program, to those that might ease the guilt of air travelers worried about their contribution to global warming when flying from, say, Boston to San Francisco.

Among the questions that arise: Whether the carbon reduction would happen anyway, without funding from the carbon offset, according to an article published by the Woods Hole Oceanographic Institute. An example would be a project that would pay a forest owner to avoid clearcutting when they had no plans to do so.

But a forest conservation project that only pushed logging to some other location would also not result in an actual emissions offset, nor would one that lasted for a greater length of time. 

Double counting is also a potential pitfall, Hanafi said. That is where a company in one country would pay to offset a certain amount of emissions in another country, and both the other country and the company claim credit.

EDF, World Wildlife Fund, and Oeko-Institut are developing their own new carbon credit buyers’ guide to help consumers and businesses navigate carbon offsets.

Meanwhile, there are existing certification programs. Oeko-Institut and World Wildlife Fund use Gold Standard, for example, and the Natural Resources Defense Council has a useful carbon offset policy that puts saving energy first, while adding that it uses an offset program called the Green e-Climate program, which is verified by non-profit organizations such as the Climate Action Reserve or Verra. 

Verra also helps the California Air and Resources Board administer the carbon offset program that is part of California’s cap-and-trade system.

One of Verra’s certified projects is preserving a large tropical swamp in Indonesia; another operates a wind farm in Oklahoma.

Carbon offsets will only work if they come with a commitment by their users to actually reduce their own carbon emissions as much as possible, and to support policies that get the world to a clean energy economy by 2050, Hanafi said.

“It’s not enough to purchase offsets,” he said. “You have to make that effort to close the circle on climate policy.” 

—James Bruggers

The data are pretty clear,” explained Johannes Lehmann, a soil scientist at Cornell University and leading expert on biochar. “It is one of the most important technologies we have to draw carbon dioxide from the atmosphere.”

The technical potential—what’s achievable in optimal circumstances—is somewhere between 5 to 8 gigatons of carbon dioxide a year, Lehmann explained.

Overall, global emissions from fossil fuels were 37 gigatons in 2019.

Biochar is a high-grade form of charcoal that’s created when biomass—from plant material or manure—undergoes a process called pyrolysis, in which the biomass is heated in a low or no-oxygen environment. The result is a carbon-dense material that, when buried in the soil, can store carbon there indefinitely, and has added benefits, including enriching soil fertility and improving tolerance to drought. 

Spent plant material and animal waste release carbon dioxide quickly. Biochar locks away the carbon in that material and waste, potentially for thousands of years. 

“There’s not driving anymore and completely cutting off fuel use—that would be helpful,” Lehmann said. “But in terms of withdrawing CO2, there’s a limited amount of options, and biochar is one of those half-dozen options that can be deployed.”

The potential is huge, but like other land-based drawdown options, challenging for reasons that have little to do with science. The potential is on a similar scale, meaning each strategy represents a tool in a tool box, not a complete solution on its own.

Like planting new forests or soil carbon sequestration, the hurdles are economic, social and political. The challenge is finding the political will and economic incentives, Lehmann said.  

“If we can decrease the barriers to entry with subsidies or other help, that’s what we should be doing,” Lehmann said. “Once biochar is in there, it’s hard to get out. I think it’s a no-regrets strategy.” 

—Georgina Gustin

Hydrochlorofluorocarbons (HCFCs), man-made chemicals refrigerants used in air conditioners and refrigeration systems, are potent greenhouse gases that also deplete atmospheric ozone. The chemicals were introduced in the 1980s as a replacement for chloroflourocarbons, CFCs, artificial chemicals that were even worse for the ozone layer and for the climate.

HCFCs are currently being phased out worldwide under a binding, international agreement known as the Montreal Protocol. Starting in 2020, the United States can no longer produce or import most HCFCs according to the agreement. 

The chemicals are, however, still widely used in existing air conditioning and refrigeration systems. The most common HCFC, HCFC-22 is a climate “super-pollutant,” 1760 times more potent as a greenhouse gas than carbon dioxide.

Hydrofluorocarbons (HFCs), a chemical replacement for HCFCs, do not play a significant role in ozone depletion but are still highly potent greenhouse gases. HFC-134a, the chemical refrigerant that replaced HCFCs in cars, is 1300 times more effective at warming the atmosphere than carbon dioxide.

An amendment to the Montreal Protocol that was ratified in 2016 and took effect in 2019 will phase out HFC production in the coming years and drive the use of chemical refrigerants that are less harmful for the climate.

Known as the Kigali Amendment to the Montreal Protocol, the agreement could help avoid up to 0.5°C of additional warming by 2100, according to the Institute for Governance & Sustainable Development (IGSD)

The United States has yet to ratify the Kigali Amendment, but, unlike the Paris Climate Agreement, the Montreal Protocol and its amendments are binding, with sanctions for countries that do not ratify.

In 2033, refrigerants produced in a country that has failed to ratify the amendment could be barred from being exported to countries that have signed on. If the United States has not ratified by then, American chemical manufacturers estimate they would lose out on billions of dollars each year in potential exports. 

The agreement’s binding requirements and near-universal membership—every UN member country has signed the Montreal Protocol and more than 100 have ratified the Kigali Amendment—have made it arguably the most effective international environmental treaty.

Without the Montreal Protocol, the use of CFCs and other ozone depleting chemicals could have had a climate impact as large as that from carbon dioxide, the largest contributor to climate change, a 2007 study published in the Proceedings of the National Academy of Sciences concluded.    

“It’s astounding how successful it has been,” Durwood Zaelke, president of the Institute for Governance and Sustainable, said. 

—Phil McKenna

It’s true. Drawdown, an international group of researchers that recently evaluated potential solutions to reduce global warming, found that reducing emissions of fluorocarbons used in refrigeration and air conditioning is one of the most important things that can be done, along with building wind farms and installing solar power, to limit future warming.

Efforts to reduce greenhouse gasses have historically focused on carbon dioxide, the largest contributor to global warming, but other greenhouse gases including methane, nitrous oxide and fluorocarbons, are also significant contributors to climate change.

Many fluorocarbons are climate “super-pollutants”—on a pound-for-pound basis, fluorocarbons are hundreds to thousands of times more potent than carbon dioxide. This means that even small volumes of emissions, like those that escape from millions of individual air conditioners when the units are disposed of at the end of their useful lives, can have a major climate impact.

Some fluorocarbons are also “short-lived climate pollutants,” meaning that they remain in the atmosphere for a relatively short period of time, from several years to several decades. Carbon dioxide, by comparison, can remain in the atmosphere for centuries. The short atmospheric life of some greenhouse gasses creates an opportunity for those looking to combat climate change. Reining in emissions of fluorocarbons and other short-lived-climate-pollutants can reduce the rate of climate change in the near-term, as countries try to tackle carbon dioxide emissions.

So why do fluorocarbons not get more press attention? Part of the answer is that a little known international treaty, the Montreal Protocol, has been very successful at phasing out the worst fluorocarbons, chemicals that were not only bad for the climate but also created the so-called “ozone hole.”

Hydrofluorcarbons, HFCs, the most widely used fluorocarbons in production today, do not deplete atmospheric ozone but are potent greenhouse gasses. The use of HFCs is still quite small, but could skyrocket in the coming decades because air conditioning in developing—and rapidly warming—countries is expected to grow exponentially.  

“Only about 1 percent of current heating of the atmosphere is caused by HFCs, but production of them is expected to increase very dramatically over the next 30 years unless action is taken to reduce them,” Dan McDougall, a Senior Fellow with the United Nations Climate and Clean Air Coalition said. 

—Phil McKenna

Carbon dioxide is the leading driver of climate change because so much of it is emitted into the atmosphere by humans, primarily from burning fossil fuels. But other gases, climate “super-pollutants,” like methane, nitrous oxide and fluorinated gases including CFCs, are much more potent pound-for-pound than carbon dioxide. 

So what makes super-pollutants so effective at warming the planet?  

“The short answer is they absorb outgoing terrestrial radiation more efficiently molecule for molecule than CO2,” Drew Shindell, an Earth science professor at Duke University, said.

Energy from the sun travels as sunlight, most of which passes through the atmosphere and is absorbed by the Earth’s surface, warming it. Some of that heat then radiates back out toward space in the form of lower energy, thermal waves that can be absorbed by the atmosphere. This absorption or trapping of thermal energy as it is radiating back out toward space is the greenhouse effect that warms the planet.

Most of the thermal energy that the atmosphere absorbs is absorbed by water molecules that occur naturally. Carbon dioxide absorbs thermal energy at many of the same wavelengths as water molecules. The net effect is that carbon dioxide is not a very potent greenhouse gas on a per molecule basis, because much of the thermal energy that can be absorbed by carbon dioxide is already being absorbed by water vapor.

Other greenhouse gases like methane, nitrous oxide and CFCs absorb thermal energy at wavelengths that differ from the wavelengths absorbed by water and CO2 making them highly potent greenhouse gases.

“The importance of any individual gas is a function of what wavelength it absorbs at, and what else might be absorbing at those wavelengths,” Shindell said. 

Methane and nitrous oxide are tens to hundreds of times more efficient at absorbing thermal radiation in the atmosphere, “but some of these fluorinated gases, they are just super absorbent at some of those wavelengths, more than 10,000 times as efficient as CO2,” Shindell said.  

Another factor that has an impact on warming is how long each of the different gases remains in the atmosphere. Carbon dioxide can stay in the air for centuries, while other greenhouse gases like methane and some fluorinated gases are much shorter lived, sticking around for a matter of years. Reducing emissions of these so-called “short-lived climate pollutants” can be an effective way to combat climate change in the near term, while working to address longer-lived carbon dioxide emissions. 

— Phil McKenna

In short, and in relation to the first part of the question, the answer is, “No,” said Sarah Kaufman, the associate director for the Rudin Center for Transportation and a professor at New York University’s  Wagner School.

Tailpipe emissions make up a massive amount of the country’s carbon emissions, and Kaufman said both electrifying vehicles and expanding public transit—which transports more people for less energy than private vehicles—are needed to avoid the worst of the climate crisis by the end of the century.

In the United States, transportation is the largest contributing sector of carbon dioxide emissions, making up nearly a third of the country’s total emissions, according to data from the Environmental Protection Agency. Private vehicles make up about 60 percent of that.

So how long would it take to electrify enough vehicles to “zero out” those transportation-related emissions? Kaufman said she doesn’t know. But, she said, what she does know is that even if we electrified the more than 270,000 vehicles on U.S. roads today, the nation’s power grid wouldn’t be able to handle it—especially with climate change increasingly straining it with extreme weather and heat.

In August 2020, a series of extreme storms in the Northeast and Midwest knocked out power for hundreds of thousands of people, while ongoing record-high temperatures in California forced utilities to shut off electricity for hundreds of thousands of customers to avoid overloading the power grid because of a massive spike in energy demand.

“If our grid can’t stand up to storms (or heat waves), then it certainly can’t power the amount of driving that Americans do,” she said. 

—Kristoffer Tigue

The American Public Transportation Association's main job is to advocate for public transit across the United States and Canada, from big agencies like the MTA in New York City to small fleets in rural and suburban communities, and everything in between. 

Paul Skoutelas, president and CEO of APTA, which has 1,500 member organizations, said the industry was hit hard by the Covid-19 pandemic, which is affecting the way that funding and improvements are approached. Ridership on rail systems was down 90 percent, and on bus systems was down 70 percent. Both rider fares and tax dollars fund public transit systems, and both revenue sources have been affected by the struggling economy.

A $25 billion stimulus in March helped the industry, but more is needed to help stabilize the industry and improve ridership rates, Skoutelas said.

Prior to the pandemic, he said, ridership rates were on the rise.

“I have no doubt that in due time we will begin to bring back those riders,” he said. “It’s going to take a bit of time—it could take a couple of years or more—that we will be back on that trajectory. I believe if we put in place the right policies and investment, we’ll see great growth in transit and our communities will come to rely on transit even more than they do today.” 

—Katelyn Weisbrod

All-electric vehicles are more climate friendly than gasoline or diesel vehicles because producing the electricity needed for power generates lower emissions than burning fossil fuels. But EVs are far from emissions-free, which is why environmental advocates highlight that walking and biking are the most climate friendly forms of transportation, followed by public transit.

The extent of the advantage for EVs varies depending on the emissions in the local power grid, so an EV in a region that relies heavily on coal to produce electricity, like the Midwest, would have more emissions than one in a place that has more renewable energy, like California. The Union of Concerned Scientists is among the organizations that have done research that compared emissions from EVs and gasoline vehicles and showed some of the regional differences.

Researchers also have also done comparisons that take into account the emissions from obtaining raw materials and manufacturing EVs and gasoline vehicles. Transportation & Environment, a Belgian nonprofit, took this approach to looking at emissions from vehicles in Europe. The organization found that EVs have lower emissions than gasoline and diesel vehicles, but also that there were big variations from country to country. For example, an EV has less of an emissions advantage over a gasoline-powered vehicle in Poland because that country’s electricity grid has unusually high emissions.

As the electricity grid gets cleaner, the climate benefits of EVs are increasing. The combination of rising EV use and a transition to clean sources of electricity are essential to reducing emissions enough to stave off the most destructive effects of climate change. 

—Dan Gearino

The Kigali Amendment is an international agreement to phase down the production and use of hydrofluorocarbons (HFCs) to address climate change. HFCs are potent greenhouse gases that are widely used today, primarily as a chemical refrigerant in air conditioning and refrigeration and in foam insulation.

HFCs were identified as one of the six main greenhouse gases, alongside carbon dioxide, methane, nitrous oxide and two others, in the 1990s, when they first started being used as a replacement for CFCs and HCFCs, chemicals that were also potent greenhouse gases and destroyed atmospheric ozone. An international agreement known as the Montreal Protocol began phasing down CFCs and HCFCs in the 1990s after scientists discovered that they had created a so-called “ozone hole” over Antarctica.

The switch to HFCs solved the problem of atmospheric ozone depletion, but it didn’t address the climate concerns associated with synthetic chemical refrigerants. HFCs are hundreds to thousands of times more potent as a greenhouse gas than carbon dioxide, the primary driver of climate change. In 2013, scientists concluded that if HFC use continued unabated, the chemical would by itself contribute an additional half a degree of warming by 2100.

At a Montreal Protocol meeting in Kigali, Rwanda, in 2016, government officials from around the world passed a binding resolution known as the Kigali Amendment that required the phasing down of HFCs.

As of July 2021, more than 120 countries including China, the leading producer of HFCs today, have ratified the amendment. While the United States has not formally ratified the agreement, it passed bipartisan legislation that requires the same 85 percent reduction in HFC production and importation by 2036, as required under the amendment.   

“It will essentially eliminate warming from one of the six main greenhouse gasses,” Durwood Zaelke, president of the Institute for Governance and Sustainable, said of the Amendment. 

—Phil McKenna

The 1997 Kyoto Protocol is an international agreement on climate change that aimed to reduce greenhouse gas emissions to 5 percent below 1990 levels by 2012. The agreement, which came into force in 2005, required only developed countries, also known as “Annex I” parties, to cut their greenhouse gas emissions and penalized those countries for non-compliance. Developing countries, “non-Annex I” parties, like India and China, though major emitters, were not required to reduce emissions.

The difference in treatment between developed and developing countries was born out of the recognition that industrialized countries are principally responsible for the high levels of greenhouse gases in the atmosphere. On the other hand, small and developing countries—China and India are exceptions—historically have contributed very little to the problem and are least able to adapt to the effects of climate change. Cumulatively over time, the United States has contributed about 25 percent of the world’s greenhouse gas emissions, the most of any single country.

Though President Bill Clinton signed the Kyoto Protocol in 1998, the Senate, in a 95 to 0 vote, passed a resolution declaring that it would not ratify a climate treaty that would “result in serious harm to the U.S. economy” or that had binding greenhouse gas reduction obligations for the United States but not for developing countries. Ratification was required for the treaty to become legally binding on the United States. President George W. Bush ‘unsigned’ the treaty in 2001.

Of the 191 countries that are parties to the Kyoto Protocol, 37 have binding reduction targets. Between 2008 and 2012, those countries reduced emissions over 22 percent compared to 1990 levels, surpassing the agreement’s 5 percent goal. Intended to help countries make emission reductions, the treaty has three market-based mechanisms: a carbon market, and two emission offset programs.

The Kyoto Protocol was born out of the 1992 United Nations Framework Convention on Climate Change (UNFCCC), which was the first, foundational and primary mechanism for the world’s nations to cooperate on climate change. Parties to the UNFCCC, including the United States, meet each year at the “Conference of the Parties” (COP) to discuss how to stabilize greenhouse gas levels in the atmosphere. 

One of the principles underpinning the UNFCCC is that countries have “common but differentiated” responsibilities for addressing climate change since they vary in their contribution to the problem and their capacity to adapt to its effects. The framework is based on scientific evidence showing that human activity has led to increases in atmospheric greenhouse gases which is causing long-term and irreversible effects.

In 2015, another UNFCCC-based treaty was born: the Paris Agreement, which aims to limit global temperature increase to 1.5 degree Celsius above the pre-industrial level. Unlike the Kyoto Protocol, the Paris Agreement does not mandate legally-binding emission cuts and has one reduction framework for all countries, not just developed nations. Every five years parties are required to submit non-binding “Nationally Determined Contributions” with pledges to lower national emissions. The agreement also incorporates the UNFCCC obligation for developed countries to activate public and private financial support for developing countries’ adaptation to climate change effects.

Because the Paris Agreement’s emission reduction commitments are non-binding, the Obama Administration took the position that the Senate did not need to ratify the agreement for the United States to become a party. In 2017, President Donald Trump announced his intent to withdraw from the Paris Agreement effective November 4, 2020. In 2021, President Joe Biden re-joined the agreement.

—Katie Surma

On December 12, 2015, representatives of 197 countries met in Paris and adopted the first binding climate agreement that obligated nearly all nations on Earth to undertake ambitious efforts to curb greenhouse gases and address the impacts of global warming.

The accord was a landmark because negotiators overcame the monumental challenge that had stymied progress for two decades: How to share responsibility for reducing global greenhouse gas emissions fairly among rich and poor nations.

Fast-growing China, India, Brazil, and Indonesia refused to agree to the same targets and timetables as industrialized nations like the United States and European countries,  which had built their wealth with the help of fossil fuels since the start of the Industrial Revolution. And the United States—which historically has contributed more greenhouse gas pollution than any other nation—would not sign on to any deal that did not require emissions cuts by rapidly developing countries like China and India that would be leading emitters in the decades ahead. The 1997 Kyoto protocol failed because of this standoff.

For the 21st annual round of climate negotiations ending in Paris in 2015, legacy-minded U.S. President Barack Obama and his negotiators pushed for a deal that obliged every country—no matter its stage of economic development—to contribute to a climate solution. But in order to win buy-in from all countries, the agreement was crafted without enforceable targets. Each nation would determine its own contribution and timetable.

Michael Oppenheimer, a climate scientist and director of the Center for Policy Research on Energy and the Environment at Princeton University, said that because of the lack of mandates, the Paris agreement could be seen as a step backward, signaling countries' lack of commitment. But in another sense, it reflects the years of work to design a system that could get countries to cut emissions, despite the political challenges.

"The Paris agreement formalized this new way of looking at climate agreements,"  Oppenheimer said. The idea was that a "name and shame" process, public announcement of goals and critical review by other countries, would push nations in the direction of actually setting credible goals and making a reasonable attempt to meet them.

The Paris Agreement that resulted was grounded in the original United Nations Framework Convention on Climate Change signed at the 1992 Earth Summit in Rio.; it was not a "treaty" that created new international legal obligations. Obama could sign it into force instead of having to send it to the Senate for ratification. Although the original UN convention passed by a voice vote in 1992, getting two-thirds of Senators to ratify any international climate treaty had become unimaginable in a Congress with increasingly acrimonious partisan divisions.

"If we follow through on the commitments that this agreement embodies, history may well judge it as a turning point for our planet," Obama said, upon signing the Paris accord. 

The first pledges nations made under the accord fell well short of the action needed to meet the Paris goal of limiting global warming to below 2 degrees Celsius. But negotiators envisioned that nations would ratchet up their ambition over time, with new pledges at least every five years.

Oppenheimer said it is too early to say if the Paris approach will be successful. "It may take until the end of this decade until we can tell," he said. "The real issue is how committed are the governments of the important emitting countries, the U.S., China, the EU, Russia, Japan, and India, to making emissions reductions—not just making up targets, but implementing those targets as firmly as is under their control." 

— Marianne Lavelle

Global warming has rapidly increased the risk of dangerous wildfires in several ways. Warmer temperatures dry out trees, brush and grass, enabling vegetation to burn more readily and spread faster after a fire ignites. Research also shows that global warming has lengthened the wildfire season substantially in many regions. The combined result is that fires are bigger, hotter and burning faster in areas and seasons where they were once rare.

Several recent studies have also directly attributed wildfires to global warming, including vast blazes in Siberia in 2020, and the “Black Summer” wildfires in Australia in late 2019 and early 2020. 

Nerilie Abram, a climate extremes researcher with Australian National University and the Australian Centre of Excellence for Climate Extremes, says there is also evidence that global warming is raising regional wildfire risks in ways that aren’t captured by direct attribution studies. The warming of the oceans is shifting the path of rainy storms away from southern Australia, she said, resulting in a regional drying trend that makes fires more likely. 

—Bob Berwyn