Fingerprint Evidence for Human Effects on Climate: Advances After the 2009 Endangerment Finding

Abstract

Here we briefly review key advances in the field of climate fingerprinting. Fingerprint studies rely on pattern information to identify human and natural influences on Earth's climate. Our focus is on advances after 2009—the date of the finding by the U.S. Environmental Protection Agency (EPA) that emissions of six different greenhouse gases affect Earth's climate and endanger human health and welfare. 

In contrast to the conclusions from a 2025 review of climate science issued by the U.S. Department of Energy (DOE), we demonstrate that post-2009 scientific advances have markedly increased confidence in the identification of significant anthropogenic contributions to global climate change. These advances were enabled by longer and improved observations of climate change, by large single-model and multi-model ensembles of simulations that yield estimates of forced climate change signals and natural variability, and by the application of climate fingerprint methods to a wide array of independently monitored variables. Increasingly, scientists are now able to quantify the impact of human-caused climate change on the probability and intensity of certain types of extreme event, particularly in the case of heat waves and the heavy rainfall in some regions. In tandem with such scientific advances, global warming has also advanced: the post-2009 period included the 10 warmest years in instrumental surface temperature records, enhancing the signal of human-caused warming relative to intrinsic variability. 

The evidence for pervasive human fingerprints throughout Earth's climate system is incontrovertible.

Plain Language Summary

This is a brief review of the history of climate fingerprinting, and of the scientific progress in this field since 2009. Fingerprint studies rely on information about the patterns and timing of climate change to identify human and natural signals in observations. A July 2025 report of the U.S. Department of Energy (DOE) questioned the credibility of fingerprint evidence, and challenged the scientific basis for the 2009 Endangerment Finding—the legal determination that human-caused climate change poses a clear and present danger to the health and welfare of U.S. citizens. 

We demonstrate that the evidence for large, human-caused climate change signals was already compelling in 2009 and has strengthened significantly since then. The DOE report fails to reflect either the weight of this evidence or the progress since 2009. Human influence is now identifiable throughout Earth's climate system, and is increasingly affecting the ability of societies and ecosystems to thrive. 

The need and scientific rationale for the Endangerment Finding is now greater than ever.