New scientific evidence strengthens case for regulating greenhouse gases


After spending its first two years unraveling critical domestic climate protections, the Trump administration took its alternative climate facts to the international stage recently, holding an event to promote coal and other fossil fuels at the United Nations talks in Poland. At the same time, a tide of scientific reports confirms the seriousness of the climate-change challenge, and the compelling motivation for rapid action. In particular, a new independent assessment that we and our colleagues just released reveals strengthened scientific support for regulating greenhouse gases under the Clean Air Act.

The Clean Air Act is the principal mechanism by which the U.S. government has protected Americans from the dangers of air pollution. In response to a petition filed by states and environmental groups, the Supreme Court ruled in 2007 that the Environmental Protection Agency (EPA) must regulate greenhouse gases under the Clean Air Act, if it finds that those gases “endanger the public health and welfare.” Neither the expected effectiveness of available regulatory measures nor the possibility of societal adaptation relieves the responsibility to act.

{mosads}In response to this ruling, in 2009 EPA issued an Endangerment Finding for six atmospheric greenhouse gases, determining that, by causing climate change, those gases threaten public health and welfare. Over the past decade, EPA has undertaken a number of rulemaking actions. These include increasing mileage standards for cars and light trucks, restricting emissions from electricity-generating power plants (known as “the Clean Power Plan”) and reducing methane emissions from oil and gas wells. These policies were also the basis for much of the national emissions reductions pledged by the U.S. to meet its commitments under the UN Paris Agreement. Trump’s EPA has begun rolling back all of these commitments.

Together with a group of experts from around the country, we conducted a systematic assessment of the scientific evidence that has emerged since the Endangerment Finding. Our conclusion is that evidence for endangerment from climate change, while overwhelming in 2009, is even stronger and more comprehensive now. 

The Endangerment Finding evaluated risks in eight major areas:

  • public health
  • air quality
  • food production and agriculture
  • forestry
  • water resources
  • sea level rise and coastal areas
  • energy, infrastructure and settlements
  • ecosystems and wildlife

Our study finds that the evidence for endangerment has increased in all eight of these areas.

Further, there is now strong evidence of risks to sectors and processes that were not included in the original finding, particularly ocean acidification, violence among people and groups, national security and economic well-being.

Much of the new evidence involves recent extreme events, such as the heat and drought that caused acute crop declines in the central U.S. in 2012, the storm surge flooding that occurred during Superstorm Sandy and other hurricanes, and the recent wildfires that have devastated areas of California and the West. Powerful new analytical approaches document the way that climate change has already increased the odds of events like these.

This new scientific evidence has important implications in the current policy environment. First, President Trump and members of his administration have repeatedly emphasized uncertainty about the relationship between human-generated greenhouse gases and climate change. However, our study shows that the evidence that human-caused climate change is real and endangers American people and ecosystems is even stronger now than when the Supreme Court ruled that EPA cannot “avoid its statutory obligation by noting the uncertainty surrounding various features of climate change”. 

Second, the Supreme Court held that EPA cannot decline to regulate a pollutant once EPA has determined endangerment. The Trump administration’s actions to weaken U.S. greenhouse gas regulations thus run contrary to the greatly increased evidence of severe and pervasive impacts, many of which extend beyond those considered in the original Endangerment Finding. Increased evidence for harm motivates stronger rather than weaker policies.

As scientists, we have a responsibility to accurately articulate the state of knowledge, and the limits of that knowledge. In the case of greenhouse gases, the evidence that formed the basis for EPA’s Endangerment Finding was strong in 2009 and has become much stronger since. That evidence clearly shows that emissions of greenhouse gases are altering the climate system, impacting public health and welfare, and intensifying risks for current and future generations. 

Science supports climate action, not as a matter of politics, but as a matter of law.

Noah S. Diffenbaugh is the Kara J Foundation Professor and Kimmelman Family Senior fellow at Stanford University.

Christopher B. Field is the Perry L. McCarty Director of the Stanford Woods Institute for the Environment and the Melvin and Joan Lane professor for Interdisciplinary Environmental Studies at Stanford University. 

Philip B. Duffy is president and executive director of the Woods Hole Research Center.

Tags Christopher B. Field Climate change Donald Trump Environment Noah S. Diffenbaugh Philip B. Duffy
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