Roger Pielke Jr. is a senior fellow at the American Enterprise Institute and author of the Honest Broker Substack.
The climate apocalypse isn’t around the corner after all. That’s the upshot of a recent report from the international panel that supplies official “scenarios” to researchers, governments and banks. It turns out that the most extreme assumptions about the future — the doomsaying predictions embodied in the worst-case scenario known as RCP8.5 — are “implausible.” In their place, Dutch researcher Detlef van Vuuren and his co-authors have proposed new ones that will form the basis of the United Nations’s next major climate assessment.
The substance of the paper, released last month, won’t shock anyone who has followed the subject scrupulously. The old scenarios described an impossibility, a world committed to the increasing consumption of coal at the expense of all other energy technologies. Scenarios based on those faulty assumptions nevertheless caught on: They dominated the assessments of the Intergovernmental Panel on Climate Change, academic papers and media reports that warned of a looming catastrophe.
The scenarios aren’t just wonky inputs to research. National climate assessments that inform policy in the United States‚ Britain, Germany, Canada, Australia, Japan and the Netherlands all emphasize them. More than 150 central banks calibrate capital stress tests against them, and lawyers cite them in litigation. It’s no stretch to say that even though most people have never heard of them, the scenarios influence decisions that affect everyone.
In a February 2021 paper, University of British Columbia professor Justin Ritchie and I explained that such work “distorted the view of our climate future.” It’s good, then, to have a more sensible understanding of things. Based on preliminary estimates, the new scenario framework brings projected warming down sharply — from about 4.8 degrees Celsius above preindustrial levels by 2100 to about 2.6 degrees. At the low end, the scenarios with the most rapid rates of emissions reduction have also been retired, affirming that the 1.5 Celsius temperature target of the 2015 Paris Agreement is infeasible.
The committee that produced the new scenario set deserves credit. It could have quietly swapped the old scenarios for slightly less extreme ones, held on to the Paris goal and pretended that little had changed. It didn’t, and the consequences will reverberate through climate policy for years. But four problems remain.
First, the new highest emissions scenario still rests on an inflated population projection — with more than 14 billion people on Earth by 2100. The U.N. expects roughly 10 billion in its medium projection, and many demographers believe it will be less than that. A back-of-the-envelope estimate suggests that using a more realistic population outlook reduces projected 2100 warming by another half-degree Celsius.
Second, the new “middle” scenario, marketed as a forward projection of current policies, is considerably more pessimistic than its peers. The International Energy Agency, which independently tracks what policies governments have enacted, anticipates that emissions will fall through the end of the century. In contrast, the new “current policy” scenario projects the opposite.
Third, there is no capacity to test whether any climate scenario corresponds to the real world, setting the stage for repeating the problems that gave us RCP8.5. Climate scenarios and the projections built off of them are so important in research and policy that their plausibility should be assessed as they are created, not after they have already been widely used.
Fourth, climate scenarios are produced by a small committee that operates with no governmental oversight, public consultation or accountability proportionate to its influence. Scenarios and scenario-based projections shape trillions of dollars in regulatory decisions, bank capital and infrastructure planning. The assumptions that underlie them may have once been contained within the boundaries of science. No more.
The new scenarios will have significant implications. Among them: The IPCC should accurately label its new high-end scenario as a thought experiment, not a forecast. Scientific journal editors should require that every paper that still uses the old, implausible scenarios clearly acknowledges as much in print. The next U.S. National Climate Assessment should drop the retired scenarios, and central banks should no longer require stress tests based on them. Insurance and infrastructure planners should likewise reexamine past decisions based on faulty inputs. Apocalyptic-sounding climate research has no place in the newsroom anymore, either.
Science works because it corrects course when off track. The most extreme scenarios have met an overdue but welcome demise. The question now is whether the rest of the world will follow.
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