Trump Administration Moves to Limit Use of Worst-Case Climate Scenarios in Federal Policy

The Trump administration has proposed a retroactive revision to the Fifth National Climate Assessment, aiming to restrict federal agencies from using the report's most severe emissions projections when drafting regulations or designing infrastructure. The move, initiated three years after the assessment was published in 2023, targets the use of "worst-case" scenarios that model a future with unchecked greenhouse gas emissions and rapid warming.[1][4]

The proposed changes focus on the Representative Concentration Pathways (RCPs), specifically RCP 8.5, which models a future where global emissions continue to rise throughout the 21st century. The White House argues that this scenario is increasingly improbable given recent shifts toward renewable energy and that its continued use artificially inflates the projected costs of climate change, leading to overly burdensome regulations.[2]

Under the new directive, federal agencies would be instructed to prioritize mid-range scenarios, such as RCP 4.5, which assume significant global emissions reductions in the coming decades. This shift would fundamentally alter the baseline for federal policy, affecting everything from the design standards for coastal military bases to the social cost of carbon used in cost-benefit analyses for new energy projects.[1][4]

The National Climate Assessment, mandated by Congress in 1990, is the US government's definitive report on the impacts of climate change. It is produced by the US Global Change Research Program, a consortium of 13 federal agencies. The fifth iteration, released in 2023, warned of accelerating impacts across all US regions and sectors, heavily citing the high-emissions scenarios to illustrate the risks of inaction.[1][3]

Environmental groups and climate scientists have sharply criticized the proposed revision, arguing that it represents political interference in established science. The Environmental Data and Governance Initiative characterized the move as an attempt to "amend" the scientific record to justify deregulation, noting that while RCP 8.5 may be less likely than previously thought, it remains a critical tool for understanding the upper bounds of climate risk.[3][4]

The debate over RCP 8.5 has been ongoing within the scientific community for several years. Some researchers argue that the scenario, which assumes a massive expansion of coal use, is no longer a plausible "business-as-usual" baseline. However, others maintain that it remains relevant, particularly given the uncertainties surrounding climate feedback loops and the potential for emissions to rebound.[2]

The administration's push to revise the assessment aligns with its broader deregulatory agenda. By lowering the projected costs of climate change, the administration can more easily justify the repeal of emissions standards for power plants and vehicles, and streamline the approval process for fossil fuel infrastructure.[1][4]

The proposed changes are currently undergoing interagency review and are expected to face significant legal challenges if finalized. Environmental organizations have indicated they will sue to block the revisions, arguing that they violate the Global Change Research Act of 1990, which requires the assessment to reflect the best available science.[1][4]