Roger Pielke is an American political scientist and a nonresident senior fellow at the American Enterprise Institute. He is not a knee-jerk climate alarmist or denier.
Pielke is a long-time critic of the Intergovernmental Panel on Climate Change (IPCC) and its assessments of the impact of climate change.
The last two years have seen some extraordinary changes in the debate over climate change. The counterrevolution is being led by what the mainstream media calls "climate deniers" (a deliberate takeoff of "Holocaust deniers") but can more accurately be referred to as "climate realists."
Pielke, the environmental scientist Steven Koonin, Judith Curry, the former chair of Georgia Tech’s School of Earth and Atmospheric Sciences, the Danish political scientist Bjorn Lomborg, and Michael Shellenberger, the former activist and author of Apocalypse Never: Why Environmental Alarmism Hurts Us All, among others, questioned the orthodoxy. They didn't deny that the climate was changing. Their sin was in not catastrophizing climate change.
For years, the most terrifying media headlines and worst-case policy projections were fueled by a specific baseline scenario known as RCP 8.5 (Representative Concentration Pathway 8.5) and its updated counterpart, SSP5 8.5 (Shared Socioeconomic Pathway 5 - Radiative Forcing 8.5). Both designations reflected the widely held belief that we were doomed by the year 2100 unless we drastically reduced carbon emissions.
The RCP and SSP5 emerged in response to an expected massive, highly implausible surge in global coal use (a fivefold increase by 2100), leading to a catastrophic atmospheric temperature rise of 4-5 degrees centigrade above pre-industrial levels.
However, the IPCC has increasingly sidelined these trajectories, shifting the scientific consensus away from an inevitable global apocalypse toward a more nuanced, manageable reality.
That new reality includes (finally) the acknowledgment that there is no demonstrable connection between climate change and severe weather. The dramatic spike in global financial losses from natural disasters is primarily driven by societal and economic growth, not an exponential increase in storm intensity. More people are living in harm's way, and significantly more expensive infrastructure is being built along vulnerable coastlines and floodplains.
Peilke has been a major critic of the IPCC for many years. And now, he has the receipts to prove one of his major criticisms: that the IPCC exaggerates the bad news in IPCC assessments.
A new preliminary paper by Galiani et al. claims that "the IPCC Summary for Policymakers (SPM) is biased toward making claims more extreme than the underlying science represented elsewhere in the IPCC reports, according to Pielke in his The Honest Broker substack.
Galiani et al. scored ~114,000 matched claim pairs drawn from all six IPCC Assessment Reports (1990–2023) and 116,000 newspaper articles from ten major US and UK outlets, using three independent large language models — GPT-5-mini, Claude Haiku 4.5, and Gemini 2.5 Flash — to evaluate each pair on the three dimensions: severity shift, uncertainty compression, and scenario salience. The headline result is unambiguous: at every measured stage, in every Assessment Report, claims shift systematically toward the more severe end of the scientific ranges presented by the IPCC in its Technical Summary.
The dominant effect is severity shift — the tendency to emphasize the upper end of reported quantitative ranges while backgrounding or ignoring the lower end. At the TS-to-SPM stage, severity shift ranges from +4% to +13% of the maximum possible upward distortion under their unitless ordinal scale (across the six Assessment Reports, peaking in AR4 (2007). Media coverage adds a further +5% to +9% bias on top of what the SPM already contains.
"Uncertainty compression — the stripping of calibrated IPCC confidence qualifiers — is a secondary but consistent effect," writes Pielke. "However, the analysis fails to recognize that the largest scenario bias effect is already baked into the severity shift."
By removing the most extreme, physically impossible scenarios from active consideration, the baseline for global planning has shifted. The future is no longer framed as an unavoidable apocalypse, but as a complex challenge of balancing energy transitions with economic reality.
Galiani et al. is the "first systematic, cross-validated, multi-cycle empirical measurement of how IPCC climate science is transformed as it moves from technical assessment to policy summary to media coverage," Pielke notes. The scientists found "a consistent amplification bias by the IPCC and in the media, across 33 years, six Assessment Reports, and using three independent AI scoring systems."
I'm not sure that the IPCC is going to change how it reports its findings to better reflect the science done. But at least we know that whether it was a deliberate act of scientific malfeasance or a casualty of groupthink, the IPCC and the media need to do a better job of releasing facts to the general public.
More importantly, Galiani et al. measure only two transitions in a seven-stage chain. The stages they do not assess — from CMIP scenario selection through the published literature to IPCC chapter assessments — carry potential amplification that could also be significant. We already know that the CMIP scenario prioritization process has biased climate science towards implausibly extreme scenarios for decades.
Perhaps most importantly, Galiani et al. offer the promise that AI tools can improve the practice of scientific assessment in climate and beyond.
As I often say, if the IPCC did not exist, we’d have to invent it. Since we have it, the top priority should be to improve it, because assessment matters.
Governments responding to the IPCC assessments have already spent trillions of dollars. It would be nice if the bias — intentional or not — could be kept to a minimum in assessing the impact of climate change on our societies.
