Washington (United States) (AFP) - Climate lawsuits seeking massive damages from fossil fuel companies increasingly hinge on this question: how reliably can scientists pin specific extreme weather events to human-caused climate change?

They can do so very confidently for some phenomenon including heat waves and heavy rainfall – but much less so for others, according to a major new report published Thursday by the United States’ top science advisory body.

Entitled “Attribution of Extreme Weather and Climate Events and their Impacts,” the 254-page paper updates a 2016 assessment by the same institutions, the National Academies of Sciences, Engineering, and Medicine (NASEM).

“The models that we use to do these studies have to be fit-for-purpose, and they have been demonstrated to be fit-for-purpose for these event types that we say we have more confidence in,” James Hurrell, a professor of atmospheric science at Colorado State University and chair of the committee that wrote the report, told AFP.

Confidence drops sharply however for local-scale events such as thunderstorms and tornadoes, which climate models still struggle to simulate at such fine resolution, he added.

Operating under a charter signed in 1863 by president Abraham Lincoln, the prestigious academies are independent nonprofit institutions tasked with advising the government on scientific policy.

But President Donald Trump has attacked the very idea that burning fossil fuels is warming the planet.

- Getting specific -

Scientists have no such doubts. They have known for decades that climate change is altering the frequency and intensity of several types of extreme weather events, including hurricanes, heat waves and extreme rainfall.

But the field of attribution science allows them to move beyond detecting broad trends to investigating individual events – what the authors call extreme event attribution (EEA) – which can provide vital information to policymakers.

EEA studies compare an event’s characteristics, such as its probability and intensity in the current climate, to a “counterfactual” world without human-caused emissions.

The authors found that overall, EEA capabilities have improved markedly over the past decade, thanks to advances in understanding physical drivers of events, expanded observational data from satellites and radar, new statistical techniques and better models.

But the gains are uneven. Confidence estimates are also lower for underdeveloped parts of the world, where a lack of consistent, long-term records limits attribution science’s reach.

The authors called for a common framework for attribution studies, as there can be “confusion among the public and other stakeholders when studies of the same event produce different results.”

- Sowing doubt -

Still, the results are likely to boost the multitude of lawsuits working their way through courts across the country.

Oregon’s Multnomah County, for example, is suing fossil fuel giants for more than $51 billion over pollution that fueled a deadly 2021 heat dome in the Pacific Northwest, during which hundreds died.

Ahead of the report’s publication, Republican lawmakers sought to cast doubt on the authors’ work, sending a letter in April to the president of NASEM alleging bias and demanding details on the authors’ professional ties.

Energy In Depth, an oil industry blog, singled out Delta Merner, a scientist with the nonprofit Union of Concerned Scientists, for criticism in a January 2, 2025 post, and she left the panel the same day.

Hurrell said he was aware of the “chatter,” but added: “I can honestly tell you that in no way did any of that outside chatter affect my work as chair of the committee, nor did it affect the final report that was produced.”

At the federal level, the Trump administration has sued Democratic-led states seeking climate damages from oil and gas majors, and has sought to strike down state “Climate Superfund” laws requiring polluters to pay for the consequences.

Republicans in Congress, meanwhile, have introduced the “Stop Climate Shakedowns Act,” a bill that would block climate damage lawsuits from proceeding in court – a move critics call a de facto immunity shield for fossil fuel companies.