On July 29, the Environmental Protection Agency (EPA) began the formal process of repealing the endangerment finding—the legal basis for regulating greenhouse gas emissions under the Clean Air Act. EPA’s immediate target is to roll back regulation of motor vehicle emissions, but successful repeal of the endangerment finding would also prevent Clean Air Act-based regulation of emissions from “stationary sources” like power plants.

The endangerment finding, issued in 2009, determined that greenhouse gas emissions harm public health and welfare. The science of climate change was robust enough to easily establish this in 2009. Ten years later, when the first Trump administration considered overturning the endangerment finding, expert scientist colleagues and I analyzed the scientific evidence and found the case for endangerment was even stronger then. It is far stronger than that today, partly because of advances in science, such as modeling and monitoring, and partly because, as warming has progressed, the human consequences of climate change have become much more severe.

Given this, how does the EPA justify trying to repeal the endangerment finding? The EPA relies in part on a new, specially-commissioned report issued by the Department of Energy (DOE), which reassesses climate science and the impacts of climate change on the US.

If the administration wanted a robust and credible review of climate science and climate impacts on the US, however, it should have relied on the National Climate Assessment (NCA), a report required every four years by the Global Change Research Act of 1990. This serves precisely the ostensible purpose of this DOE report: an independent review of climate science and its implications for the US.

However, the NCA is much more credible and authoritative than DOE’s ad hoc report, because it is produced by a much larger and more diverse set of authors (the 5th edition of the NCA had over 500 authors representing all 50 US states, and at least some of the territories), vs. five authors for the recent DOE report; and because the NCA is subject to multiple levels of peer review, including by the US National Academy of Sciences.

If the administration wanted a robust assessment of climate science, it should not have removed the 5th NCA from government websites or halted the in-process 6th NCA, both of which it did earlier this year. 

The Fourth National Climate Assessment, by the way—which was released during the first Trump Administration and approved by the Trump White House—included language explicitly saying that greenhouse gas emissions cause climate change and that climate change is negatively impacting the lives of Americans–exactly the standard that has to be met to establish endangerment. If greenhouse gas emissions were dangerous during the first Trump administration, one wonders why they would not be dangerous now.

Additional independent scientific bodies have affirmed the societal harms of climate change. Foremost among these is the Intergovernmental Panel on Climate Change (IPCC), which is uniquely authoritative because of its number and diversity of authors, extent of peer review, government approvals, and process transparency. For the most recent IPCC Assessment Report, 782 scientists (and hundreds more contributing authors) analyzed more than 66,000 peer-reviewed studies. In the four summary documents (each of which is around 35 pages), every sentence is approved unanimously by governments from around the world—including the US government. This rigorous, inclusive, and transparent process makes IPCC the gold standard in policy-relevant climate science. 

It is appropriate that discussions of the dangers posed by greenhouse gas emissions focus mainly on climate change. However, there are additional mechanisms, independent of climate change, by which emissions of the most important greenhouse gases, carbon dioxide and methane, are harmful. These two independent mechanisms provide an additional basis for a finding of endangerment and for the regulation of these greenhouse gases. 

First, carbon dioxide emissions cause ocean acidification, which harms ocean ecosystems generally, including shellfish. Shellfishing is an important industry in the United States and elsewhere.

Second, emissions of methane contribute to air pollution via the formation of ground-level ozone, which is toxic to humans, animals, and plants (including crops). While climate change can also impact air pollution and air quality, the clear effects of methane emissions on air quality are independent of the simultaneous climate impacts of methane. A study by the International Energy Agency found that methane abatement in the fossil fuel sector could avoid nearly a million premature deaths by 2050 from direct improvements in air quality alone. Methane abatement can also save tens of millions of tonnes of crop losses every year from improved air quality.

Although the cost of potential regulations is not relevant to a finding of endangerment, in their proposed rulemaking EPA argues against greenhouse gas regulations on the basis of cost. This argument fails to recognize not only the economic costs of climate change, but also the immediate effects of particulate pollution from fossil fuel burning, which kills tens of thousands of Americans every year. (Some estimates put that mortality as high as hundreds of thousands annually.) The good news is that this mortality has declined as the use of coal in the US has also declined–thanks in large part to EPA regulations.

Finally, climate change has progressed to the point today where the scientific consensus on climate change is confirmed by the lived experience of Americans. Perhaps most prominent among the impacts felt is extreme weather, which has become severe enough to become a risk not only to individuals but to the insurance industry and threatens home values. Americans can see for themselves the harms of climate change, and that’s why they strongly support measures to control greenhouse gas emissions.

The most foundational responsibility of government, in my view, is to protect the physical health and safety of the citizens. The EPA, in particular, has the mission of “protecting people and the environment from significant health risks.” With this proposed action, EPA and the Trump administration are walking away from this most fundamental duty. The science here is clear, but it does not speak for itself. It is up to us to make our voices heard.