The EPA’s 2009 Endangerment Finding has underpinned almost all U.S. efforts to reduce greenhouse gas emissions, making it a prime target for the Trump administration’s rollback of climate policies. A day-one executive order included a directive to review the “legality and continuing applicability” of the finding. On March 12, the EPA announced that it would potentially rescind the Finding, and the announcement was formalized with a proposed rule on July 29.
Repealing the Finding would undo more than a decade of work that has made American communities healthier, skies clearer of smog and other pollution, and contributed to the country’s decreasing carbon emissions.
What is the Endangerment Finding?
The Endangerment Finding is a pivotal determination by the EPA, issued in response to the 2007 U.S. Supreme Court Case Massachusetts vs. EPA. In that case, the court held that the EPA has the authority to regulate greenhouse gases under the Clean Air Act, and that after it has made a finding of endangerment, the agency cannot refuse to regulate these gases.
Additionally, the EPA found that greenhouse gases in the atmosphere are both a hazard to public health and that motor vehicle emissions contribute to this pollution. In the years since, the EPA has built on the original ruling and issued subsequent endangerment findings relating to aircraft and utility emissions under other provisions of the Clean Air Act .
Why is the Endangerment Finding important?
As a result, the Endangerment Finding has become the legal foundation for essentially all federal regulation of greenhouse gas emissions in the U.S. – including motor vehicle tailpipe emissions and power plant rules.
The EPA’s proposed rule would repeal all greenhouse gas emissions standards for light-duty, medium-duty, and heavy-duty vehicles and engines, and would preempt any state fuel efficiency or vehicle emissions laws or regulations. Furthermore, this repeal could be a foundation for undoing greenhouse gas emissions regulations on stationary sources like power plants or oil and gas facilities.
The Endangerment Finding is based on sound science
The attempt to repeal the Endangerment Finding is emblematic of the current administration’s disregard for scientific consensus around the causes and impacts of climate change.
The original finding draws from expertise at the U.S. Global Change Research Program, the Intergovernmental Panel on Climate Change (IPCC), and the National Academies of Sciences. It examined public health and public welfare in the U.S., with a focus on air quality, food production and agriculture, forestry, water resources, sea level rise and coastal areas, energy, infrastructure, and settlements, and ecosystems and wildlife. The EPA received over 380,000 public comments, the majority of which provided support for the Finding.
In 2018, Dr. Philip Duffy, then-president of Woodwell Climate Research Center, led a review of the scientific foundation of the Endangerment Finding. That work, published in the journal Science, found that “for each of the areas addressed in the EF, the amount, diversity, and sophistication of the evidence has increased markedly, clearly strengthening the case for endangerment. New evidence about the extent, severity, and interconnectedness of impacts detected to date and projected for the future reinforces the case that climate change endangers the health and welfare of current and future generations.”
What’s next for climate policy?
The legal validity of the administration’s proposed rule was contested almost immediately and challenges will likely continue to roll in even if the rule is made official.
The EPA has extended a public comment period on this topic through September 22, 2025. The recently released Department of Energy (DOE) report, A Critical Review of Impacts of Greenhouse Gas Emissions on the U.S. Climate, which challenges scientific consensus by claiming that carbon dioxide-induced warming appears to be less damaging economically than commonly believed, serves as a foundation for the EPA’s proposed rule. That report is also open for public comment through September 2, 2025.
The National Academy of Sciences has fast-tracked its scientific review of the impacts of greenhouse gases on human health in order to inform the decision within the comment period, and has requested contributions from scientists and experts in the fields of public health, extreme weather, climate modeling, agriculture, and infrastructure. Woodwell Climate is contributing to the opportunities for public comment and scientific engagement to aid future consideration of this, and similar, proposals in courts and encourages members of the public to do the same.
Canada’s fire season has barely started and it’s already on track to break records. So far, NOAA has documented more than 2,000 wildfires that have resulted in the forced evacuation of over 100,000 people across Canada. The most recent bout of fires burning in Ontario and Quebec has sent smoke southward into the Eastern U.S., causing record levels of air pollution in New York and warnings against outside activity as far south as Virginia.
Only a little over a month into the wildfire season, fires have already burned 13 times more land area than the 110-year average for this time of year, and they show no sign of stopping, according to Canadian publication The Star. Indigenous communities, some of whom live year-round in remote bush cabins, have been particularly harmed by the blazes.
According to Woodwell Climate Senior Scientist Dr. Jennifer Francis, the phenomenon of winds pushing smoke down to the northeastern U.S. has been linked to rapid Arctic warming caused by climate change.
In the upper atmosphere, a fast wind current called the jet stream flows from west to east in undulating waves, caused by the interaction of air masses with different temperatures and pressures, particularly between the Arctic and temperate latitudes.
As global temperatures have risen, the Arctic has warmed two to four times faster than the average global rate. Dr. Francis stated in an interview in the Boston Globe that the lessening of the temperature differences between the middle latitudes and the Arctic has slowed down the jet stream, which results in a more frequent occurrence of a wavy path.
Another factor contributing to the widespread smoke is an ongoing oceanic heat wave in the North Pacific Ocean. The blob of much-above-normal sea water tends to create a northward bulge in the jet stream, which creates a pattern that sends cooler air down to California and warm air northward into central Canada—resulting in the persistent heat wave there in recent weeks. Farther east, the jet stream then bends southward and brings the wildfire smoke down to the Northeast.
“Big waves in the jet stream tend to hang around a long time, and so the weather that they create is going to be very persistent,” Dr. Francis said. “If you are in the part of the wave in the jet stream that creates heat and drought, then you can expect it to last a long time and raise the risk of wildfire.”
The wildfires are also decimating North American and Canadian boreal forests, the latter of which holds 12 percent of the “world’s land-based carbon reserves,” according to the Audubon Society<./a> And three quarters of Canada’s woodlands and forests are in the boreal zone according to the Canadian government.
“The surface vegetation and the soil can dry out pretty dramatically given the right weather conditions. For this fuel, as we call it in fire science, it often just takes one single ignition source to generate a large wildfire,” said Woodwell Climate Associate Scientist Dr. Brendan Rogers.
As the climate continues to warm, Dr. Rogers said the weather conditions that lead to fuel drying and out-of-control wildfires also increase. This creates a feedback loop. Heat waves caused by greenhouse gas emissions increase the prevalence of wildfires. The fires in turn destroy these natural carbon sinks and, in turn, speed up climate change.
While the ultimate solution to breaking this feedback loop lies in reducing emissions and curbing climate change, Dr. Rogers and other researchers at Woodwell Climate have conducted research into fire suppression strategies that could help prevent large boreal fires from spreading and help keep carbon in the ground.
A study conducted in collaboration with Woodwell and other institutions found that suppressing fires early may be a cost-effective way to carbon mitigation. Woodwell Climate’s efforts also include mapping fires, using geospatial data and models to estimate carbon emissions across large scales, and looking at the interplay between fires and logging.
“Reducing boreal forest fires to near-historic levels and keeping carbon in the ground will require substantial investments. Nevertheless, these funds pale in comparison to the costs countries will face to cope with the growing health consequences exacerbated by worsening air quality and more frequent and intense climate impacts expected if emissions continue to rise unabated. Increased resources, flexibility, and carbon-focused fire management can also ensure wildlife, tourism, jobs, and many other facets of our society can persevere in a warming world,” Dr. Rogers said.