By Roger Pielke Jr., originally posted at The Honest Broker, April 29, 2026
The international committee responsible for the official scenarios that feed into climate modeling, which 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. (Emphasis, links added by Principia Scientific)
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 that 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. Extreme computer-modeled scenarios drive the attribution science industry, which has been trying to link hydrocarbon use to bad weather.
Let’s get started…
The new scenarios come from the Coupled Model Intercomparison Project (CMIP) — a project of the World Climate Research Programme (WCRP), cosponsored 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 responsible for developing the scenarios that Earth system models use 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.
In a paper released earlier this month, Van Vuuren et al. (VVetal26) introduce a new set of seven scenarios.
The authors write of the obsolete high-end emissions scenarios (emphasis added):
For the 21st century, this range will be smaller than assessed before: on the high-end of the range, the CMIP6 high emission levels (quantified by SSP5-8.5) have become implausible, based on trends in the costs of renewables, the emergence of climate policy and recent emission trends.
Read that again — the high-end scenarios are implausible.1
I disagree that the implausibility of the high-end scenarios resulted from the falling costs of renewables or the emergence of climate policy, but that is a debate for another day.
What matters today is that the group with official responsibility for developing climate scenarios for the IPCC and broader research community has now admitted that the scenarios that have dominated climate research, assessment, and policy during the past two cycles of the IPCC assessment process are implausible: They describe impossible futures. Research papers, governments, and media headlines frequently cite these implausible scenarios.
Tens of thousands of research papers have been — and continue to be — published using these scenarios, and a similar number of media headlines have amplified their findings, and governments and international organizations have built these implausible scenarios into policy and regulation.
We now know that all of this is built on a foundation of sand.
Read the full substack at The Honest Broker.
Wind Concerns is a collaboration of citizens of the Lakeland Alberta region against proposed wind turbine projects.