Lane Kenworthy, The Good Society
Are we causing the planet to warm? What are the potential consequences? What, if anything, should we do about it?
- Human-caused climate change
- What should we do?
- Some cause for hope
- What do Americans think?
HUMAN-CAUSED CLIMATE CHANGE
The hypothesis is relatively straightforward: In various ways, but especially by burning fossil fuels, we’ve dramatically increased greenhouse gas emissions. If the amount of greenhouse gases emitted from earth is larger than natural processes can remove, it will trap more infrared radiation (sunlight that bounces off the earth) in the atmosphere, leading to a rise in temperature. Also, warm air holds more water vapor than cold air, and water vapor causes additional trapping of heat. The planet should therefore be warming.
What does the evidence say?
Begin with the hypothesized cause. As figure 1 shows, emissions of carbon dioxide have increased steadily since 1750, when the industrial revolution began, and the rise has been especially pronounced since 1950.
As carbon dioxide emissions have increased, the amount of carbon dioxide in the atmosphere has increased. We have direct measurement of CO2 atmospheric concentration only since 1959, but data from ice core drilling in Antarctica suggest that in the 800,000 years prior to 1750, it never exceeded 300 ppm (parts per million). Between 1750 and 1959 it rose from 280 to 316. As figure 2 indicates, between 1959 and 2018 it increased from 316 to 409.1
Carbon dioxide isn’t the only problematic greenhouse gas. Methane and nitrous oxide play a role too. Here a major contributor is the raising of animals for food, which accounts for approximately 15% of all greenhouse gas emissions.2 That’s roughly the same as all cars, trucks, airplanes, and ships combined.3 Figure 3 shows that methane concentration in the atmosphere has increased sharply since scientists began measuring it in the mid-1980s. The concentration of methane is much lower than of carbon dioxide, but methane’s potency as a greenhouse gas is about 30 times greater.4
Next, the hypothesized effect. Has the planet’s temperature increased? Yes, it has. Figure 4 shows direct measurements beginning in 1880. Average temperature has risen sharply, particularly since 1950. Figure 5 shows indirect and direct measurements going back to 700. It suggests a similar conclusion.
Because the historical temperature records are incomplete, scientists introduce corrections. Are these corrections biased? This was the concern at the heart of the 2009 “climategate” controversy. However, the Berkeley Earth Surface Temperature (BEST) project has gathered together all existing temperature measures, and the data, even with no corrections, show a similar trend.5
Is this a “heat island” effect? In other words, do these measurements show warming simply because a number of the temperature stations are near towns that have been growing? No. We know this for three reasons: a heat island effect would be strongest on still nights, yet trends from data recorded on still nights are similar to those on windy nights; temperature readings from non-heat-island stations show a similar trend to those from heat-island stations; and the temperature of water at the surface of oceans shows a similar trend to that on land.6
Could the observed temperature rise be a result of something else? Probably not. Computer simulations that project temperature patterns in scenarios with little or no human emission of greenhouse gases don’t come close to matching the earth’s actual temperature patterns. As figure 6 shows, when the simulations add human-generated greenhouse gases, they closely match the observed temperature patterns.
Also, as Joseph Romm has noted, “if the warming is caused by an increase in greenhouse gases, we expect the lower atmosphere (troposphere) to warm, the upper atmosphere (stratosphere) to cool, and the boundary between them (tropopause) to rise. All of this has been observed. If, for instance, recent warming were due to increases in the intensity of radiation from the sun, then in addition to the troposphere, the stratosphere should be warming, too, which is not happening.”7
The most thorough survey of the evidence is a 2013 report by the Intergovernmental Panel on Climate Change (IPCC). It concluded that “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”8
How much consensus is there among climate scientists? In 2010, the Proceedings of the National Academy of Sciences reported the findings of a survey of 1,372 climate researchers. It found that 97-98% of those publishing in the field believe humans are causing climate change. And “The relative climate expertise and scientific prominence of the unconvinced researchers … are substantially below that of the convinced researchers.”9 A more recent study also found 97% agreement.10
A 2014 report by the Climate Change Panel of the American Association for the Advancement of Science described the scientific consensus this way: “The science linking human activities to climate change is analogous to the science linking smoking to lung and cardiovascular diseases. Physicians, cardiovascular scientists, public health experts, and others all agree smoking causes cancer. And this consensus among the health community has convinced most Americans that the health risks from smoking are real. A similar consensus now exists among climate scientists, a consensus that maintains climate change is happening, and human activity is the cause.”11
In sum, while it’s impossible to be fully certain, the computer simulations coupled with the observed evidence yield a conclusion of “extremely likely” that humans are causing climate change.
Climate change is likely to have an array of effects. Many are difficult to project, both because the climate is a complex system and because it isn’t clear how much progress we will make in slowing or reversing the carbonization of the atmosphere.
In the absence of quick and effective action to reduce greenhouse gas emissions, climate change is likely to have damaging effects on health via, among other things, heat waves, urban smog, lack of access to water, and displacement.12 In the United States, for example, the number of 100-degree-or-more days per year is projected to increase significantly almost everywhere, and by the end of the century a good bit of the country will have summer weather similar to today’s Texas and Arizona, as we see in figure 7. In some parts of the world, things will be worse. The World Heath Organization projects that, in the absence of action to slow climate change, by 2050 an additional 250,000 people (0.002% of the world’s population) will die each year directly due to greater heat.13
Climate change will increase the frequency and intensity of weather events and weather-related events — storms (hurricanes, typhoons, tornadoes), floods, droughts, fires. Figure 8 shows that extreme rainstorms, one type of event for which we have a lengthy data series, have become more common in the United States. Figure 9 shows that extreme fires have become increasingly common in California since 1990.
The most significant impact of warming could come via melting of the Greenland and West Antarctic ice sheets, each of which has enough ice to raise sea levels by 15 to 20 feet. A significant rise in sea level could threaten hundreds of millions of people who live in coastal areas. The United Nations estimates that by 2050 as many as 1 billion people, or 10% of the world’s population, may be climate migrants.14 Predicting how much the two ice sheets will melt and what impact that will have is extremely difficult. In its 2013 report, the IPCC concluded that melting from the two ice sheets may cause a sea level rise of 1 to 3 feet by the year 2100. Since then, scientists have discovered that ice loss in the Greenland and West Antarctic ice sheets has been faster in recent years than previously thought and that a large glacier in the East Antarctic ice sheet is now vulnerable to melting. According to one knowledgable observer, these recent findings “have led top climatologists to conclude that we are likely headed toward what used to be the high-end of projected global sea-level rise this century (i.e., 4 to 5 feet) and that the worst-case scenarios where humanity fails to take aggressive action to cut greenhouse gas emissions are considerably higher than that.”15
Most ominously, Gernot Wagner and Martin Weitzman estimate that in the absence of significant policy change there is perhaps a one in ten chance that the globe’s average temperature will rise by 6°C or more.16 The consequences could be quite grim, as David Wallace-Wells explains17:
“The earth has experienced five mass extinctions …, each so complete a wiping of the fossil record that it functioned as an evolutionary reset, the planet’s phylogenetic tree first expanding, then collapsing, at intervals, like a lung: 86 percent of all species dead, 450 million years ago; 70 million years later, 75 percent; 125 million years later, 96 percent; 50 million years later, 80 percent; 135 million years after that, 75 percent again. Unless you are a teenager, you probably read in your high school textbooks that these extinctions were the result of asteroids. In fact, all but the one that killed the dinosaurs involved climate change produced by greenhouse gas. The most notorious was 250 million years ago; it began when carbon dioxide warmed the planet by five degrees Celsius, accelerated when that warming triggered the release of methane, another greenhouse gas, and ended with all but a sliver of life on Earth dead.”
WHAT SHOULD WE DO?
There is considerable uncertainty about the speed and scale of climate change’s consequences for the planet and for humans and other animals. While some see this as a reason to focus on other problems where we have more knowledge about the efficacy of action and/or where the payoff will be immediate,18 our typical approach to problems where the outcome is uncertain but potentially catastrophic is to use extreme precaution in order to prevent them.19 Think of World War II, disease outbreaks, terrorism, or the “reasonable doubt” principal we use in criminal trials.
How much reduction in greenhouse gas emissions do we need? Many climate scientists believe we should aim for an increase in average temperature of no more than 1.5°C or at most 2°C (it’s already risen about 1°C). Not too long ago, knowledgeable observers calculated that this would require reducing greenhouse gas emissions by more than half by 2050 and to zero by 2100.20 More recent calculations suggest we need to move faster, cutting emissions in half by 2030 and to zero by 2050.21
How can we do it? Advocates frequently emphasize personal behaviors and lifestyles, but the key will be to change large-scale actors, institutions, and systems.22
Shift from fossil fuel energy to clean energy. Government could require the phase-out of fossil fuel energy sources by a particular date, but the most common policy tools here are carbon taxes and cap-and-trade programs. Sweden and Norway have had a carbon tax since the early 1990s, and the Canadian province of British Columbia has had one since 2008. The United States used cap-and-trade programs to successfully deal with leaded gasoline in the 1980s and acid rain pollution in the 1990s. California began a cap-and-trade program to reduce greenhouse gas emissions in 2013.23 Quebec and Ontario also have cap-and-trade programs for greenhouse gases. If necessary, government could purchase a majority stake in fossil fuel companies and rapidly reduce coal, oil, and gas production.24 To this point, congressional Republicans have blocked federal government action in the US.25
Humans currently use about 16 terawatts of energy per year. There is more than enough energy available from solar and wind, the two leading noncarbon (“renewable”) energy resources, to provide this amount and more.26 The challenge is getting it to everyone throughout the year and throughout the day. For that, we need further improvement in storage and batteries. An important advantage, however, particularly for solar energy, is that it can be generated close to where it is needed — on the roofs of buildings, houses, and parking lots. And because it is much more efficient than fossil fuel energy sources, one estimate concludes that “without changing the size of our homes, or our cars, or fundamentally changing the fabric of our lives, a fully electrified energy economy using non-carbon fuel sources would require less than half of the total amount of energy we use today.”27
The remainder of the needed noncarbon energy can be provided by a mix of biofuels, geothermal, and nuclear.28
The United States accounts for about one-fifth of worldwide carbon emissions, so we could help a lot even if we act alone.29 Better would be an international agreement that reduces emissions in other countries too. Efforts over the past several decades haven’t been very successful, though the 2015 Paris Climate Accord offered some grounds for optimism.30 An alternative to voluntary agreements, which are vulnerable to free riding, is the idea of a “climate club.” According to William Nordhaus, “Under the club rules, participating countries would undertake harmonized but costly emissions reductions…. Countries who are outside the club — and do not share in the burden of emissions reductions — are penalized…. Economic modeling indicates that the most promising penalty is uniform percentage targets on the imports of nonparticipants into the club region. A country considering whether to undertake costly abatement would have to weigh those costs against the potentially larger costs of reduced trade with countries in the club.”31
Geoengineering. We can try to alter the earth and/or its biosphere. One approach aims to limit the warming of the planet. The main idea here is to deflect more sunlight, for example by injecting large quantities of aerosols into the stratosphere. This is at best a partial approach, as it wouldn’t stop or even slow carbonization, but it might buy us some time. A second approach is to actually remove carbon from the atmosphere. In a pair of reports issued in 2015, the US National Academy of Sciences concluded that while geoengineering efforts are worth further exploration, “There is no substitute for dramatic reductions in the emissions of carbon dioxide and other greenhouse gases to mitigate the negative consequences of climate change.”32
Research. A rapid shift to noncarbon energy sources is feasible with existing technology. But this problem is so big, and political obstacles to rapid decarbonization are so formidable, that it makes sense to invest heavily in development of new energy sources, new methods of delivery, new ways of getting carbon out of the atmosphere, and more.33
How much will it cost us to prevent significant climate change? An estimate by the Congressional Budget Office puts the cost of an aggressive carbon-reduction effort at 1-3% of GDP.34 Yet not acting might be just as costly. According to one respected estimate, by William Nordhaus, the loss from a rise in temperature of 2.5°C would be about 2% of global GDP.35
SOME CAUSE FOR HOPE
There are some encouraging technological developments36:
- In the 2010s, the cost of solar panels fell by nearly 90% and the cost of wind turbines by 60%. Clean energy is now cheaper than 40% of coal plants worldwide and most natural gas plants. Partly as a result, more than 80% of all new electricity around the world in 2019 and 2020 came from clean sources, and that figure is projected to reach 95% in the early 2020s.
- The cost of batteries for electric cars is expected to reach parity with internal combustion engines by the early 2020s. And Toyota has developed a new solid-state (rather than lithium-ion) battery for electric vehicles that will allow a car to travel 300-plus miles on a charge that takes 10 minutes. Sales of internal-combustion vehicles have been declining since 2017. General Motors, the world’s third largest car manufacturer, has announced that by 2035 it will sell only zero-emission vehicles. And Ford has pledged to do so in Europe by 2030.
- Climate Trace, a coalition of nonprofits and businesses, uses artificial intelligence, machine learning, and satellite image processing to measure worldwide greenhouse gas emissions in real time, with updates every six hours. This kind of accurate, up-to-date information should help voters, activists, and other actors to monitor governments and corporations and apply pressure where appropriate.
There also are some hopeful signs on the political front37:
- Signatories to the 2015 Paris Climate Accord, including 197 nations, pledged to take action to hold “the increase in the global average temperature to well below 2°C above preindustrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels.” The Accord didn’t commit any country to particular actions. Nor did it specify rewards or punishments.
- A small but growing number of countries have passed laws requiring zero net greenhouse gas emissions (“carbon neutrality”) by 2050: Norway in 2016; Sweden in 2017; France, New Zealand, and the United Kingdom in 2019; Canada, Japan, and South Korea in 2020. In 2020 China’s government pledged to reach carbon neutrality by 2060. In 2021, the US president issued an executive order instructing the country to reach zero net emissions by 2050. In all, 125 nations, which together account for more than two-thirds of global emissions, either have adopted or are debating a goal of net zero emissions by the middle of the century.
- A small but growing number of US states have passed laws requiring large reductions in greenhouse gas emissions by 2050. In 2019, California, which has the world’s fifth largest economy, passed a law mandating zero net carbon emissions in the state’s electricity sector by 2045, and its governor issued an executive order requiring zero net emissions across the entire economy (of which electricity is just 16%) by the same year. In 2019, New York state passed a law mandating 85% reduction in greenhouse gas emissions (from 1990 levels) by 2050.
- In 2019, the Netherlands’ Supreme Court ruled that the European Convention on Human Rights requires the Dutch government to significantly reduce the country’s greenhouse gas emissions — to 25% below the 1990 level by 2020. This was the first time a court has required a nation to take action against climate change.
As of November 2020, 127 governments in countries that currently account for about two-thirds of global emissions have agreed to or are discussing pledges to reach net zero emissions by the middle of this century. Climate Action Tracker estimates that if all of these nations actually meet the targets, warming will reach 2.1 degrees. This scenario and various others are shown in figure 10.
The organization also estimates that under current policies warming will reach 2.9 degrees. That’s higher than we want, but it’s an improvement compared to the estimate as of 2015, which was 3.7 degrees.
The shift to a decarbonized world is often portrayed as a sacrifice — a reduction in our quality of life in order to save the only planet on which, as far as we can tell, human life is possible. But that’s probably the wrong image. If conversion to 100% noncarbon energy is done chiefly via electrification, the main changes in our lives will be driving electric (instead of internal combustion engine) cars, using an electric (instead of gas) cooking source, getting heating from an electric heat pump (instead of gas-powered forced air), and eating more plant-based foods. Even for those who live in rich countries, much of this will be an improvement in quality of life, not a downgrade. And for people in middle- and low-income nations, it will be an unmitigated advance.38
WHAT DO AMERICANS THINK?
As figures 11-14 show, around two-thirds of Americans believe most scientists agree global warming is occurring, believe climate change is due to human activities, worry a great deal or a fair amount about climate change, and feel there should be stricter laws and regulations to protect the environment. There is an enormous difference in these views between Americans who identify as Democrats and those who identify as Republicans.
Figure 15 shows that only half of Americans believe rising temperatures are extremely or very dangerous. Although low, this share isn’t exceptional compared to other rich democratic nations.
The hypothesis that greenhouse gas emissions are causing climate change is compelling. The evidence in support of the hypothesis is very strong, and there is near-consensus among experts about this.
The consequences will be almost entirely bad, though it is difficult to predict their magnitude or speed with much precision.
The key question is how best to slow and reverse the carbonization of the atmosphere. Here there is less agreement, though there are some encouraging developments.
- Carbon Dioxide Information Analysis Center, “800,000-year Ice-Core Records of Atmospheric Carbon Dioxide”; Earth System Research Laboratory, National Oceanic and Atmospheric Administration, “Trends in Atmospheric Carbon Dioxide”; Intergovernmental Panel on Climate Change (IPCC), “Working Group 1 Summary for Policymakers,” Fifth Assessment Report, 2013, p. 7; Wikipedia, “Carbon Dioxide in Earth’s Atmosphere.” ↩
- P.J. Gerber et al, Tackling Climate Change Through Livestock: A Global Assessment of Emissions and Mitigation Opportunities, Food and Agriculture Organization of the United Nations, 2013. See also Natasha Gilbert, “One-Third of Our Greenhouse Gas Emissions Come from Agriculture,” Nature, 2012; Rob Bailey, Antony Froggatt and Laura Wellesley, “Livestock: Climate Change’s Forgotten Sector,” Research Paper, Chatham House, 2014; J. Poore and T. Nemecek, Reducing Food’s Environmental Impacts Through Producers and Consumers,” Science, 2018; Ecofys, “World Greenhouse Gas Emissions Flow Chart”. ↩
- Julia Moskin, Brad Plumer, Rebecca Lieberman, and Eden Weingart, “Your Questions About Food and Climate Change, Answered,” New York Times, 2019. ↩
- Wikipedia, “Atmospheric Methane.” ↩
- R. Rohde, R.A. Muller, R. Jacobsen, E. Muller, S. Perlmutter, et al, “A New Estimate of the Average Earth Surface Land Temperature Spanning 1753 to 2011,” Geoinformatics and Geostatistics: An Overview, 2013. ↩
- “The Science of Climate Change,” The Economist, 2010; C. Wickham, R. Rohde, R.A. Muller, J. Wurtele, J. Curry, et al., “Influence of Urban Heating on the Global Temperature Land Average using Rural Sites Identified from MODIS Classifications,” Geoinformatics and Geostatistics: An Overview, 2013. ↩
- Joseph Romm, Climate Change: What Everyone Needs to Know, Oxford University Press, 2016, p. 10. ↩
- IPCC, “Working Group 1 Summary for Policymakers,” Fifth Assessment Report, pp. 12; Justin Gillis, “Climate Panel Cites Near Certainty on Warming,” New York Times, August 20, 2013. William Nordhaus points out that “Scientists are increasingly confident that the basic results of climate modeling are accurate. Climate models calculate that past emissions have contributed to warming of almost one degree centigrade over the last century, with rapid continued warming projected over the present century and beyond. In its 2001 report, the Intergovernmental Panel on Climate Change reported that human activity was ‘likely’ to be the source of this warming. The IPCC upgraded this evaluation to ‘very likely’ in its 2007 report and to ‘extremely likely’ in its 2013 report.” Nordhaus, “A New Solution: The Climate Club,” New York Review of Books, 2015. ↩
- William R.L. Anderegg, James W. Prall, Jacob Harold, and Stephen H. Schneider, “Expert Credibility in Climate Change,” Proceedings of the National Academy of Sciences, 2010. ↩
- John Cook et al, “Quantifying the Consensus on Anthropogenic Global Warming in the Scientific Literature,” Environmental Research Letters, 2013. ↩
- Climate Change Panel, American Association for the Advancement of Science, What We Know: The Reality, Risks, and Response to Climate Change, 2014, p. 2. ↩
- Romm, Climate Change. ↩
- World Health Organization, “Quantitative Risk Assessment of the Effects of Climate Change on Selected Causes of Death, 2030s and 2050s,” 2014, p.21. ↩
- International Organization for Migration, “IOM Outlook on Migration, Environment, and Climate Change,” 2014, p. 38. ↩
- IPCC, “Working Group 1 Summary for Policymakers,” Fifth Assessment Report, pp. 18, 21; Potsdam Institute for Climate Impact Research and Climate Analytics, “Turn Down the Heat: Why a 4°C Warmer World Must Be Avoided,” The World Bank, 2012; Romm, Climate Change, p. 94. ↩
- Gernot Wagner and Martin L. Weitzman, Climate Shock: The Economic Consequences of a Hotter Planet, Princeton University Press, 2015, ch. 3. See also Steven C. Sherwood and Matthew Huber, “An Adaptability Limit to Global Warming Due to Heat Stress,” Proceedings of the National Academy of Sciences, 2010. ↩
- David Wallace-Wells, The Uninhabitable Earth, Duggan Books, 2019, pp. 3-4. ↩
- Bjorn Lomborg, Cool It, Random House, 2007. ↩
- Martin L. Weitzman, “Fat-Tailed Uncertainty in the Economics of Catastrophic Climate Change,” Review of Environmental Economics and Policy, 2011; Gernot and Weitzman, Climate Shock. ↩
- Romm, Climate Change, p. 154. ↩
- Jesse D. Jenkins and Samuel Thernstrom, “Deep Decarbonization of the Electric Power Sector: Insights from Recent Literature,” Energy Information Reform Project, 2017; Intergovernmental Panel on Climate Change (IPCC), “Summary for Policymakers of IPCC Special Report on Global Warming of 1.5°C,” 2018; “Interview with Saul Griffith,” The Ezra Klein Show, 2019. ↩
- Emma Marris, “How to Stop Freaking Out and Tackle Climate Change,” New York Times, 2019; “Interview with Saul Griffith.” ↩
- Center for Climate and Energy Solutions, “California Cap-and-Trace”; Jennifer Medina and Matt Richtel, “Carbon Goal in California Is ‘Milestone’ on Climate,” New York Times, 2016; Brad Plumer, “How California Plans to Go Far Beyond Any Other State on Climate,” New York Times, 2017. ↩
- Kate Aronoff, Alyssa Battistoni, Daniel Aldana Cohen, and Thea Riofrancos, A Planet to Win: Why We Need a Green New Deal, Verso, 2019. ↩
- “Harry Reid: Senate Will Abandon Cap-and-Trade Energy Reform,” Christian Science Monitor, 2010. ↩
- Mark Z. Jacobson et al, “100% Clean and Renewable Wind, Water, and Sunlight All-Sector Energy Roadmaps for 139 Countries of the World,” Joule, 2017; Saul Griffith, “How Do We Decarbonize?,” Medium, 2019. ↩
- Saul Griffith, “The Green New Deal: The Enormous Opportunity in Shooting for the Moon,” Medium, 2019. ↩
- Inês Azevedo, Michael R. Davidson, Jesse D. Jenkins, Valerie J. Karplus, and David G. Victor, “The Paths to Net Zero,” Foreign Affairs, 2020. ↩
- Environmental Protection Agency, “Global Greenhouse Gas Emissions Data.” ↩
- “Climate Talks End with Modest Deal on Emissions,” New York Times, 2010; “Nations Approve Landmark Climate Accord in Paris,” New York Times, 2015. ↩
- Nordhaus, “A New Solution: The Climate Club.” ↩
- National Research Council, Committee on Geoengineering Climate, “News Release,” 2015. ↩
- Ted Norhaus and Michael Shellenberger, Break Through, Houghton Mifflin, 2007; Jim Manzi, “Keeping Our Cool: What to Do about Global Warming,” Cato Unbound, 2008; Romm, Climate Change; Kevin Drum, “We Need a Massive Climate War Effort — Now,” Mother Jones, 2019. ↩
- Congressional Budget Office, “Effects of a Carbon Tax on the Economy and the Environment,” 2013. ↩
- Paul Krugman, “Building a Green Economy,” New York Times, 2010; William D. Nordhaus, “Why the Global Warming Skeptics Are Wrong,” New York Review of Books, 2012. ↩
- Al Gore “Where I Find Hope,” New York Times, 2020; Nikkei Asia, “Toyota’s Game-Changing Solid-State Battery En Route for 2021 Debut,” 2020; Neal E. Boudette and Coral Davenport, ”G.M. Will Sell Only Zero-Emission Vehicles by 2035,” New York Times, 2021; Neal E. Boudette and Jack Ewing, ”Ford Says It Will Phase Out Gasoline-Powered Vehicles in Europe,” New York Times, 2021. ↩
- Wikipedia, “Paris Agreement”; Wikipedia, “Carbon Neutrality”; Megan Darby, “Which Countries Have a Net Zero Carbon Goal,” Climate Home News, 2019; NRDC, “Unpacking New York’s Big New Climate Bill: A Primer,” 2019; Brady Dennis, “Countries Must Ramp Up Climate Pledges by 80 Percent to Hit Key Paris Target, Study Finds,” Washington Post, 2021. ↩
- “Interview with Saul Griffith.” ↩