Climate Fingerprints Grow Stronger After EPA Pulls Finding

A five-author review published on October 12, 2026 finds climate fingerprints of human-caused warming stronger than they were in 2009.

The U.S. Environmental Protection Agency had already published its repeal of the 2009 Endangerment Finding on February 18, 2026, and that rule took effect on April 20, 2026. The new paper is now sitting in a different fight: lawsuits in the D.C. Circuit, and a fresh EPA bid to apply the same legal reading to power plants.

The Paper Landed After EPA Pulled the Finding

The review of fingerprint studies after 2009 appears in Earth’s Future, an American Geophysical Union journal, volume 14, issue 10. Benjamin Santer, a climate scientist at the University of East Anglia, led the work with Susan Solomon of MIT, David W.J. Thompson of UEA and Colorado State University, Qiang Fu of the University of Washington, and Gabriele C. Hegerl of the University of Edinburgh.

Fingerprint research uses the pattern and timing of climate change to tell human influence from natural swings. Santer’s early work fed the Intergovernmental Panel on Climate Change’s 1995 line that “the balance of evidence suggests a discernible human influence on global climate.” The new paper says that case was already strong when EPA issued the Endangerment Finding, and that 17 years of later work have made it stronger still.

FROM THE 2009 FINDING TO THE 2026 REVIEW

1. December 15, 2009: EPA finds that six greenhouse gases endanger public health and welfare under Clean Air Act Section 202(a).
2. July 29, 2025: The Energy Department releases a Climate Working Group report, and EPA Administrator Lee Zeldin signs a proposal to repeal the finding.
3. September 17, 2025: The National Academies of Sciences, Engineering, and Medicine conclude that the 2009 finding still holds and is now backed by stronger evidence.
4. February 18, 2026: EPA publishes the repeal of the finding and of greenhouse gas standards for new light-duty, medium-duty, and heavy-duty vehicles and engines.
5. April 20, 2026: The repeal takes effect, covering model years 2012 to 2027 and beyond.
6. October 12, 2026: Santer and colleagues publish the fingerprint review in Earth’s Future.

The AGU release still talks about a “move to revoke” the finding. That language is stale. The finding is already gone at the agency. What remains is whether judges restore it, and whether EPA can copy the same theory onto other sectors.

The climate science that’s been published since the 2009 Endangerment Finding is now stronger than in 2009, the evidence is incontrovertible.

Benjamin Santer, professor, University of East Anglia School of Environmental Sciences, AGU news release

What a Climate Fingerprint Study Measures

A fingerprint study does not stop at a rising global average. It asks what shape the change took, and when. Researchers run climate models with greenhouse gases, the sun, volcanoes, and other factors switched on or off, then they check which predicted pattern actually shows up in measurements from satellites, weather stations, and the ocean.

Different causes leave different marks. Extra carbon dioxide holds more heat in the lower air and helps the layer above it shed heat to space. A brighter sun would warm both layers. That mismatch is one of the oldest tests in the field, and it still does the work of separating people from nature.

THE PATTERN TESTS THESE STUDIES USE

• Vertical air: Warming in the troposphere, the lowest layer, paired with cooling in the stratosphere above it.
• Timing: A human signal that grows as greenhouse gases rise, set against the shorter noise of El Niño, volcanoes, and other natural swings.
• Extremes: Changes in the odds and intensity of heat waves and, in some regions, heavy rain, which the authors say scientists can now size more clearly.
• The whole system: Matching shifts from the top of the stratosphere to the deep ocean, in physically consistent ways.

The review concentrates on annual, decadal, and seasonal changes. It only touches the large literature on single storms and floods. Heat waves and heavy rainfall in some regions are the events the authors say researchers can now quantify with more confidence. Other extremes stay harder when the link to the long-term average is still poorly worked out.

Warming Below and Cooling Above Still Holds

The vertical pattern is the piece the Energy Department report tried to knock down. In July 2025 the Climate Working Group claimed the stratosphere has warmed since 2000, which would clash with model projections and with the expected human fingerprint.

Santer, Solomon, Thompson, and Fu answered that claim in an August 29, 2026 commentary in Earth’s Future. They wrote that the incorrect tropical stratosphere trends in a Department of Energy figure did not match the satellite records. With the right data sets, they said, model trends in tropical lower-stratosphere temperature line up with observations, and a predicted human fingerprint is identifiable with high confidence.

Cooling in the lower stratosphere, from about 15-20 km up, also comes from human-caused ozone loss. That lower-stratosphere cooling eased in the 21st century as ozone began to heal after the Montreal Protocol. Strong cooling higher in the stratosphere did not ease. Satellite records still match what current models produce for human-caused temperature change, the same group wrote in AGU Advances.

These studies reveal that many independently monitored aspects of Earth’s climate have all been altered by global warming in physically consistent ways, just as we expect, from the top of the stratosphere to the depths of the world’s oceans.

Susan Solomon, Lee and Geraldine Martin Professor of Environmental Studies, MIT, AGU news release

Hegerl said methods now also track how greenhouse gases have changed the frequency and intensity of extreme events, and how a weather event observed now has been changed by those emissions. The review ties that chain to heat stress, flooding, wildfires, and crop damage, the same class of harms the 2009 finding treated as risks to health and welfare.

The 10 Hottest Years Sharpened the Human Signal

The science did not only get better tools. The climate itself moved. The authors note that the post-2009 period included the 10 warmest years in instrumental surface temperature records. That stretch raised the human warming signal relative to the noise of natural variability.

THE SIGNAL AFTER 2009

• The record: The 10 warmest years in the instrumental surface temperature series fall in the years after the Endangerment Finding.
• The method: A larger, longer warming signal is easier to pick out from El Niño, volcanic cooling, and other short swings.
• The extremes: Heat waves, and heavy rain in some regions, are the events the authors say researchers can now tie more tightly to greenhouse gases.
• The limit: Some event types still have a weak or disputed link to the long-term mean, so those fingerprints remain incomplete.

That is an awkward fact for anyone arguing that the 2009 record was thin. The extra heat that arrived after the finding is part of why later papers speak with more confidence. It is also the heat that health and welfare claims now rest on.

A Five-Scientist Energy Report Took Aim at Fingerprints

On July 29, 2025, the Energy Department issued a critical review of greenhouse gas impacts titled “A Critical Review of Impacts of Greenhouse Gas Emissions on the U.S. Climate.” Energy Secretary Chris Wright assembled five outside scientists as the 2025 Climate Working Group: John Christy, Judith Curry, Steven E. Koonin, Ross McKitrick, and Roy W. Spencer.

The department said carbon dioxide warming appears less damaging economically than commonly believed, and that aggressive cuts may be misdirected. It also said U.S. policy actions are expected to have undetectably small direct effects on the global climate, with any effects arriving only after long delays. Santer’s team calls that assessment deeply flawed and says it skips both the weight of the 2009 evidence and the progress since.

An earlier Santer paper in AGU Advances noted that the Energy Department report was referenced 16 times in EPA’s July 2025 proposal, including on the question of attributing climate change to human causes. The same paper said the Energy Department document should not inform legal decisions on the scientific basis of the 2009 finding.

WHERE THE TWO DOCUMENTS DIVERGE

Wright framed the report as a defense of energy supply. “Climate change is real, and it deserves attention. But it is not the greatest threat facing humanity,” he said when the department released the document.

If we empower innovation rather than restrain it, America can lead the world in providing more abundant energy, lifting billions out of poverty, strengthening our economy, and improving our environment along the way.

Chris Wright, U.S. Secretary of Energy, Department of Energy announcement, July 29, 2025

A federal judge later treated the working group as an advisory committee that broke the law. On January 30, 2026, the U.S. District Court for the District of Massachusetts entered judgment in Environmental Defense Fund v. Wright, No. 1:25-cv-12249, holding that the group was not exempt from the Federal Advisory Committee Act and that it violated rules on open meetings, open records, and fair balance. DOE had already been ordered, on December 8, 2025, to release the group’s records.

Harm to Health Is Beyond Scientific Dispute

Santer’s review is not the only post-2009 stocktaking that EPA declined to follow. During the comment window on the repeal proposal, the National Academies ran a fast-track study of evidence gathered since EPA’s 2009 technical support document. The committee said it was pointed to more than 600 peer-reviewed articles.

The Academies released the report on September 17, 2025, five days before comments closed on September 22, 2025. The overarching conclusion was that EPA’s 2009 finding “was accurate, has stood the test of time, and is now reinforced by even stronger evidence.” The committee also wrote that the harm is beyond scientific dispute.

Overarching Conclusion: EPA’s 2009 finding that the human-caused emissions of greenhouse gases threaten human health and welfare was accurate, has stood the test of time, and is now reinforced by even stronger evidence.

National Academies committee, Effects of Human-Caused Greenhouse Gas Emissions on U.S. Climate, Health, and Welfare, September 17, 2025

The 2009 finding covered six greenhouse gases taken together: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. EPA issued it after the Supreme Court, in Massachusetts v. EPA, 549 U.S. 487 (2007), rejected an earlier refusal to decide the question on grounds that were not grounded in science. The National Academies noted that the Clean Air Science Advisory Committee, which the Clean Air Act tells EPA to draw on, had been disbanded in January 2025, so that statutory science channel was empty during the repeal push.

EPA’s final action did not rest only on the working group’s science brief. In the published repeal the agency said Section 202(a) does not authorize emission standards aimed at global climate change, and it did not finalize extra repeal grounds that had been floated at the proposal stage. Harvard Law School’s Environmental and Energy Law Program, which tracks the rule, says EPA’s main explanation is that it lacks authority under Section 202, a reading that, if courts accept it, would block a later administration from using that section to regulate greenhouse gases from vehicles.

Why the D.C. Circuit Holds the Climate Rules

The agency fight is over. The court fight is not. Petitions for review landed in the U.S. Court of Appeals for the D.C. Circuit within days of publication, and they are the venue Santer’s review can still reach.

THE CASES NOW BEFORE THE D.C. CIRCUIT

• Health groups: American Public Health Association and others filed on February 18, 2026, No. 26-1037.
• Young plaintiffs: Eighteen young people in Venner v. EPA filed the same day, No. 26-1038, citing the First, Fifth, and Tenth Amendments, the Religious Freedom Restoration Act, and the Clean Air Act.
• Automakers’ rivals: The Zero Emission Transportation Association filed on February 20, 2026, No. 26-1039.
• States: Massachusetts and 23 other states, plus a dozen counties and cities, filed on March 19, 2026, No. 26-1061.

In April 2026, a set of environmental and public health groups and a set of 24 state attorneys general petitioned EPA to reconsider. Both argued that the final rule relied on technical analyses completed after the comment period closed, so it was not a logical outgrowth of the proposal. Those petitions sit beside the D.C. Circuit cases, not in place of them.

If the court accepts EPA’s statutory reading, fingerprint papers become a scientific archive with no federal vehicle standard attached. If the court sends the science or the process back, the October review and the National Academies report are the record a future rule would have to confront. Either way, the extra years of fingerprint work now matter as evidence, not as a last-minute plea to an agency that has already acted.

EPA Is Extending the Same Logic to Power Plants

The vehicle finding was the first brick. On September 17, 2026, EPA published a final rule repealing most of the 2024 carbon pollution standards for fossil fuel-fired power plants. The same day it issued a supplemental proposal saying Clean Air Act Section 111 does not authorize greenhouse gas limits for those plants at all, tracking the reasoning used in the rescission of the Endangerment Finding. Comments on that proposal are due on November 2, 2026.

Santer put a second warning on the science itself. “A different kind of ‘Endangerment Finding’ is that the continuation of rigorous attribution science is endangered,” he said. “It’s inconvenient science for those who seek a fossil fuel intensive future, because it connects the dots between fossil fuel burning and harms to our personal health, to the health of our planet and to the health of our societies and economies.”

The fingerprint literature is thicker than it was in 2009, and the warmest years on the instrumental record arrived after that finding. EPA has already withdrawn the legal determination those papers were written to inform. The D.C. Circuit and the power-plant docket are where that thicker record still has somewhere to go.