US Retires Worst-Case Climate Models, Rewriting Basis for Federal Climate Planning

The White House has officially instructed federal agencies to stop using "worst-case" climate change scenarios—specifically the high-emissions pathway known as RCP8.5—as the baseline for infrastructure planning, environmental regulations, and federal grant funding. The U.S. Global Change Research Program (USGCRP), the interagency body responsible for coordinating federal climate research, published a proposed amendment to the Fifth National Climate Assessment (NCA5) this week. The amendment mandates that any federal planning relying on RCP8.5 or its successor, SSP5-8.5, must include explicit disclaimers that the scenarios are "implausible."[1][5]

The directive prohibits these high-end projections from serving as the central or "business-as-usual" baseline for funding decisions, infrastructure design, or regulatory rules. Local governments building sea walls, power grids, and zoning laws based on federal guidelines will now see those guidelines recalibrated to intermediate warming scenarios. The USGCRP director stated that the amendment is intended to ensure the federal government's principal climate assessment reflects current scientific understanding, bringing the national climate assessment back into a realm of plausible scenarios rather than extreme outliers.[1][2]

The administrative move aligns with a growing consensus in the broader climate science community. Earlier in 2026, the United Nations Intergovernmental Panel on Climate Change (IPCC) and the international climate-modeling community moved to retire RCP8.5 and similar extreme pathways from their primary reference cases. For more than a decade, RCP8.5 represented a future in which greenhouse gas emissions rose dramatically, leading to extreme warming of about 4.4 degrees Celsius by 2100. It assumed the world would burn roughly five times more coal by the end of the century and actively resist the energy transition.[7]

However, updated assessments have deemed that trajectory implausible given real-world trends. Rapid growth in renewable energy, falling costs for solar and wind power, and the plateauing of global coal use have bent the emissions curve downward. Current policies and trends now point toward 2.5 to 3 degrees Celsius of warming by 2100. While this is still enough to intensify heatwaves, droughts, and sea-level rise, it is significantly lower than the catastrophic RCP8.5 baseline that has dominated climate research and media headlines for years.[7]

While the scientific community has acknowledged the implausibility of RCP8.5, the Trump administration's mandate goes further by actively restricting agencies from using these models to justify stringent environmental regulations or infrastructure spending. The USGCRP is now led by Matthew Wielicki, a former University of Alabama geochemist appointed by the White House in July 2026. Wielicki, who has a history of criticizing mainstream climate science and arguing that prior federal assessments overstated certainty, was brought in after the administration dismissed the scientists developing the upcoming Sixth National Climate Assessment.[3][6]

Critics and environmental groups argue the administration is using a legitimate scientific recalibration as a pretext to deregulate and downplay the severe risks of climate change. They note that while the worst-case scenario has been averted, the current trajectory still poses profound risks to global ecosystems and human infrastructure. Environmental advocates warn that the administration is weaponizing a nuanced scientific update to systematically dismantle environmental protections, pointing to the dismissal of federal climate researchers as evidence of a politicized agenda.[6]

Conversely, conservative think tanks and free-market advocates have praised the retirement of RCP8.5 as a long-overdue correction. Organizations like the Competitive Enterprise Institute have long argued that the climate establishment misused the extreme scenario as a baseline projection to exaggerate the magnitude of climate risks and justify expansive government intervention. They contend that federal planning has been fundamentally distorted by these implausible worst-case scenarios, leading to misallocated infrastructure funds and overly burdensome regulations that stifle economic growth without providing proportional environmental benefits.[4]

The immediate impact of the amendment will be felt across federal agencies, which must now audit their existing policies and funding criteria to ensure they do not rely on the retired models without proper disclosure. Engineering standards, insurance catastrophe models, and state regulatory requirements that draw on federal baselines will likely face pressure to adjust their risk assessments accordingly. Retiring these models forces a recalibration of federal planning toward lower warming projections, fundamentally altering how the U.S. government prepares for climate risks over the coming decades.[1][3][5]