Jean Jouzel

The growth rate of greenhouse gas (GHG) climate forcing increased rapidly in the last 15 years to about 0.5 W/m2 per decade, as shown by the “colorful chart” for GHG climate forcing that we have been publishing for 25 years (Fig. 1).[1] The chart is not in IPCC reports, perhaps because it reveals inconvenient facts. Although growth of GHG climate forcing declined rapidly after the 1987 Montreal Protocol, other opportunities to decrease climate forcing were missed. If policymakers do not appreciate the significance of present data on changing climate forcings, we scientists must share the blame.

22 of the planet’s 34 vital signs are at record levels, with many of them continuing to trend sharply in the wrong direction. This is the message of the sixth issue of the annual “State of the climate” report. The report was prepared by an international coalition with contribution from the Potsdam Institute for Climate Impact Research (PIK) and led by Oregon State University scientists. Published today in BioScience, it cites global data from the Intergovernmental Panel on Climate Change (IPCC) in proposing “high-impact” strategies.

Une bonne politique climatique repose sur une bonne science climatique. Et une bonne science climatique repose sur le Groupe d’experts intergouvernemental sur l’évolution du climat (GIEC*) depuis sa création par les gouvernements en 1988. Le GIEC est composé de dizaines de milliers de scientifiques issus de dizaines de pays, qui couvrent les multiples facettes du « pourquoi » et du « comment » du changement climatique. Il établit une ligne consensuelle dans des rapports (*) volumineux publiés tous les cinq ou six ans. Il a si bien rempli cette mission qu’il a reçu en 2007 le prix Nobel de la paix aux côtés de l’ancien vice-président Al Gore.

This article examines the technocentric bias that characterizes climate mitigation literature, focusing on the reports of the IPCC's Working Group III. This bias stems from structural features of the scientific field that prioritizes innovation, leading to the overrepresentation of technological solutions in climate research. Funding mechanisms further reinforce this tendency by incentivizing collaboration with industrial R&D, creating a self-reinforcing loop in which scientific authority and industrial interests converge. The IPCC's institutional positioning—as a policy-relevant yet politically cautious body—amplifies this dynamic by favoring allegedly “cost-effective” technological pathways that lack practical feasibility.

Climate sensitivity is substantially higher than IPCC’s best estimate (3°C for doubled CO2), a conclusion we reach with greater than 99 percent confidence. We also show that global climate forcing by aerosols became stronger (increasingly negative) during 1970-2005, unlike IPCC’s best estimate of aerosol forcing. High confidence in these conclusions is based on a broad analysis approach. IPCC’s underestimates of climate sensitivity and aerosol cooling follow from their disproportionate emphasis on global climate modeling, an approach that will not yield timely, reliable, policy advice.

A critical examination of climate science risk assessments and the growing challenge from global actuaries

In a rapidly changing climate, evidence-based decision-making benefits from up-to-date and timely information. Here we compile monitoring datasets (published at https://doi.org/10.5281/zenodo.15639576; Smith et al., 2025a) to produce updated estimates for key indicators of the state of the climate system: net emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. This year, we additionally include indicators for sea-level rise and land precipitation change. We follow methods as closely as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One report.

– how climate scientists and the IPCC still won’t tell the truth about accelerating climate change.

Global temperature for 2025 should decline little, if at all, from the record 2024 level. Absence of a large temperature decline after the huge El Nino-spurred temperature increase in 2023-24 will provide further confirmation that IPCC’s best estimates for climate sensitivity and aerosol climate forcing were both underestimates. Specifically, 2025 global temperature should remain near or above +1.5C relative to 1880-1920, and, if the tropics remain ENSO-neutral, there is good chance that 2025 may even exceed the 2024 record high global temperature.

Figure TS.15 | Contribution to (a) effective radiative forcing (ERF) and (b) global surface temperature change from component emissions for1750–2019based on Coupled Model Intercomparison Project Phase 6 (CMIP6) models and (c) net aerosol ERF for 1750–2014 from different lines of evidence.