Multnomah County’s $51 billion climate lawsuit against America’s energy producers was never going to age well. It was built on activist science, conflicted lawyers, and a worst-case scenario its own modelers admitted was implausible. This month, the bottom fell out.
In April 2026, the international scientific committee that designs climate scenarios for the United Nations officially retired SSP5-8.5 — the corollary to the infamous RCP 8.5 — declaring it “implausible” and dropping it from the framework that will underpin the next IPCC assessment. That is the very pathway that has powered nearly every catastrophic climate headline you have ever read, and it is the scaffolding behind tens of billions of dollars in damage claims now winding their way through American courts.
For more than a decade, RCP 8.5 was marketed to judges, regulators, and reporters as “business as usual.” It was nothing of the kind. Its own creators designed it as a 90th-percentile stress test built on absurd assumptions — 12 billion people on Earth, technology frozen in place, a fivefold global increase in coal, more coal than geologists believe can even be mined. Scientists began warning that it was implausible in 2017. A 2020 paper in Nature said it “becomes increasingly implausible with every passing year.” The Biden EPA quietly pulled it from regulatory cost-benefit analysis in 2022.
They knew. They used it anyway.
By 2024, new academic studies citing RCP 8.5 were still appearing at a rate of 25 per day. The U.S. National Climate Assessment used it as recently as 2023. The Climate Judiciary Project trained more than 2,000 judges on materials built on it. And plaintiffs’ lawyers built billion-dollar damage claims on it.
The institutional footprint is staggering. Over 140 central banks stress-tested the global financial system against it. The World Bank applied it across more than 100 countries. The United Kingdom built two decades of national adaptation planning around it. Germany, Canada, Australia, the Netherlands, and Japan each embedded it in building codes and flood maps.
Multnomah County is one of the most brazen examples of how this fiction was weaponized in court. The county, home to the city of Portland, claims that major energy companies were a substantial factor in causing and exacerbating the 2021 heat wave and is seeking $51 billion in damages. The core of that claim is an “attribution science” study by Christopher Callahan and Justin Mankin that purports to assign dollar values to heat-related damages from individual energy producers — claiming Chevron alone caused as much as $3.6 trillion in losses. That study draws its projections directly from the high-emissions scenarios the U.N. has now retired.
It gets worse. According to Chevron’s filings, plaintiffs’ lead attorney Roger Worthington had undisclosed financial involvement in at least two of the studies the county presents as neutral, peer-reviewed science. Early drafts of the Mankin study were hosted on Worthington’s law firm website. An early version acknowledged funding from the Environmental Law Institute’s Climate Judiciary Project — the same group running “neutral” judicial education seminars — before that disclosure was quietly scrubbed from the published version.
So the science was manufactured. The funding was hidden. The judges were trained on the same compromised material. And the underlying scenario has now been officially retired by the U.N. itself.
This is not climate science. It is climate racketeering, exposed.
Multnomah is not alone. The Boulder case heading to the Supreme Court next term, the Honolulu suit, the Minnesota complaint, and dozens of others all draw on the same body of work. Every active climate damages claim in the United States now rests on a scientific foundation that the international scientific community has formally repudiated.
And the cost of letting these cases proceed falls squarely on American families. If courts award damages anywhere near what plaintiffs seek, the bill will not stop at the boardroom door. It will flow straight to consumers through higher pump prices, higher utility bills, higher insurance premiums, and a higher cost of capital baked into every barrel of oil and every kilowatt-hour of electricity produced in this country. Climate litigation is, functionally, a regressive tax imposed by trial lawyers rather than elected legislatures, hitting hardest the working families who can least afford it.
Courts should treat this seriously. Judges should exclude RCP 8.5-based evidence and expert testimony at the gate, the same way they would exclude any other retracted study. The EPA’s rescission of its 2009 Endangerment Finding should accelerate — the regulatory edifice was built on the same retired scenarios. Central banks should rebuild their stress-test frameworks on plausible trajectories. And the Federal Judicial Center was right to pull its climate science chapter from the judicial reference manual earlier this year. Every state and federal court training program should follow.
The doomsday scenario is officially retired. So is the case for these lawsuits.
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The Honorable Jason Isaac is the CEO of the American Energy Institute and previously served four terms in the Texas House of Representatives.
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