Multnomah County, Oregon, home to Portland, filed a $51 billion climate lawsuit against major energy producers in 2021. The county alleges that fossil fuel companies were a substantial factor in causing and exacerbating the heat wave that year, seeking damages based on attribution science studies that assigned dollar values to emissions from individual companies.

In April 2026, the international scientific committee that designs climate scenarios for the United Nations officially retired SSP5-8.5 — the corollary to RCP 8.5 — declaring it "implausible" and removing it from the framework underpinning the next Intergovernmental Panel on Climate Change assessment. That scenario had powered many public-facing climate projections and served as the foundation for damage calculations in litigation.

RCP 8.5 was originally designed by its creators as a 90th-percentile stress test based on extreme assumptions, including 12 billion people on Earth, technology frozen at current levels, and a fivefold global increase in coal use. Scientists began warning that it did not represent realistic projections beginning in 2017. A paper published in Nature in 2020 stated the scenario "becomes increasingly implausible with every passing year."

The Biden EPA quietly removed RCP 8.5 from regulatory cost-benefit analysis in 2022, according to the report. By 2024, academic studies citing the scenario were still appearing at a rate of approximately 25 per day, and the U.S. National Climate Assessment used it as recently as 2023.

The institutional reach was substantial. More than 140 central banks stress-tested global financial systems against the high-emission pathway. The World Bank applied it across more than 100 countries. The United Kingdom built two decades of national adaptation planning around the scenario, while Germany, Canada, Australia, the Netherlands, and Japan embedded it in building codes and flood maps.

What the Left Is Saying

Climate science advocates argue that retiring a single emissions pathway does not undermine the broader scientific consensus on climate change. Proponents note that multiple scenarios remain in use, including high-end projections that still support significant climate risk. They contend that even if RCP 8.5 was an extreme case, it illustrated real consequences of unchecked emissions growth.

Environmental law groups maintain that attribution science is a legitimate and evolving field. The Climate Judiciary Project, which provided educational materials to more than 2,000 judges, argued its programs present peer-reviewed research to help courts understand technical climate evidence. Supporters say the legal strategy reflects courts taking seriously the documented impacts of fossil fuel production on communities.

Plaintiffs' attorneys in Multnomah County argue that energy companies knew about climate risks for decades and engaged in campaigns to obscure scientific understanding. They contend that regardless of which emissions pathway serves as a baseline, the causal link between fossil fuel production and measurable harms is supported by substantial evidence beyond attribution studies.

What the Right Is Saying

Conservatives and industry groups say the retirement of SSP5-8.5 validates long-standing concerns about junk science in climate litigation. They argue that courts should exclude expert testimony based on retracted or discredited scenarios, just as they would with any other debunked scientific foundation.

The U.S. Chamber of Commerce and energy industry representatives contend that lawsuits like Multnomah's represent an attempt to impose massive liability through the judiciary rather than through elected legislatures. They say this effectively creates climate policy without democratic input while targeting companies that provided energy Americans depended on for generations.

Legal scholars aligned with defendants argue that excluding RCP 8.5-based evidence is a matter of basic evidentiary standards. They note that if expert testimony rests on assumptions the scientific community itself has rejected, courts have an obligation to scrutinize such evidence rigorously before allowing juries to consider damage calculations running into trillions of dollars.

What the Numbers Show

The Multnomah County lawsuit seeks $51 billion in damages from major energy producers based on attribution studies claiming specific dollar amounts of climate harm attributable to individual companies. One study by researchers Christopher Callahan and Justin Mankin claimed Chevron alone caused as much as $3.6 trillion in losses, according to court filings.

The scenario underpinned stress tests conducted by more than 140 central banks worldwide and was embedded in policy frameworks across at least five major developed economies over two decades. The Climate Judiciary Project trained over 2,000 judges on materials built using the now-retired pathway.

The Biden EPA's removal of RCP 8.5 from regulatory analysis occurred in 2022, though the agency did not publicly announce the change. By that year, academic studies citing the scenario were still being published at a rate of approximately 25 per day, according to the source report.

Other major climate lawsuits pending include cases brought by the City of Boulder, Colorado (headed toward Supreme Court review), Honolulu, Hawaii, and Minnesota. Each draws on attribution science methodologies similar to those used in Multnomah County.

The Bottom Line

The retirement of SSP5-8.5 by the scientific committee that designs U.N. climate scenarios marks a significant development for dozens of pending climate damage lawsuits across the United States. Defense attorneys are expected to file motions arguing that expert testimony and damage calculations built on the now-discredited pathway should be excluded from proceedings.

Courts will need to determine whether attribution science methodologies can stand independently of specific emissions pathways, or whether the underlying assumptions must also be revisited. Legal observers say these evidentiary questions could reshape climate litigation strategy going forward.

The EPA's prior quiet removal of RCP 8.5 from regulatory analysis may provide precedent for judicial scrutiny of scenarios used in court. The Federal Judicial Center pulled its climate science chapter earlier this year, though the circumstances were not detailed in available materials.

What to watch: Whether judges grant motions to exclude RCP 8.5-based expert testimony, how plaintiffs' attorneys respond with alternative methodological frameworks, and whether the Supreme Court's anticipated review of the Boulder case addresses evidentiary standards for climate attribution science.