From: The Honest Broker
By: Roger Pielke Jr.
Date: April 29, 2026
RCP8.5 is Officially Dead
“[T]he high-emissions RCP8.5 scenario has long been described as a “business-as-usual” pathway with a continued emphasis on energy from fossil fuels with no climate policies in place. This remains 100% accurate . . .“ — from 2021, Chris Field (co-chair of IPCC WG2 AR5) and Marcia McNutt (president of U.S. National Academy of Sciences, Engineering, and Medicine )
Note: Work in progress — Caveat lector!
The international committee responsible for the official scenarios that feed into climate modeling that are the basis for most projective climate research and the assessments of the Intergovernmental Panel on Climate Change (IPCC) has just published the next generation of climate scenarios.
Big news: The new framework has eliminated the most extreme scenarios that have dominated climate research over much of the past several decades — specifically, RCP8.5, SSP5-8.5, and SSP3-7.0. This is an absolutely huge development in climate science which will have lasting impacts across research and policy.
The future is not what it used to be.
Today’s post commends the researchers who have brought climate scenarios more in line with current understandings, but also raises some significant continuing issues with the scenarios.
Let’s get started . . .
The new scenarios come from the Coupled Model Intercomparison Project (CMIP) — a project of the World Climate Research Programme (WCRP), co-sponsored by the World Meteorological Organization, the International Science Council, and UNESCO’s Intergovernmental Oceanographic Commission.
Under CMIP, now in its seventh iteration, sits another little-known committee with responsibility for developing the scenarios necessary for earth system models to project future climate.¹ That committee — called ScenarioMIP — just published the new scenario framework that will underpin the IPCC’s Seventh Assessment Report (AR7) and much of the research that it will draw upon. (continue reading)