In June 2019, 91 signatories sent a petition to the Presidents of the Italian Republic, the Chamber of Deputies, and the Senate, challenging “climate alarmism” and calling for a scaling back of emissions reduction policies. As documented by Climalteranti.it, the vast majority of the signatories had no specific expertise in climate science. The petition did not challenge any specific IPCC data on the matter; rather, it challenged the intensity with which the scientific community communicated its findings. During the same period, the IPCC’s Sixth Assessment Report was finalizing analyses that would classify human influence on the climate system as “unequivocal”: a term that, in the IPCC lexicon, carries no associated probability, as it denotes a directly observable fact that transcends the probabilistic scale. In public discourse, “skepticism” and “doubt” describe very different positions. In the case of the petition, they described the same thing.
The IPCC uses two distinct scales to communicate scientific uncertainty. The first is a confidence scale (ranging from very low to very high), based on the quality and quantity of the available evidence and the level of agreement among researchers. The second is a probability scale, with different levels ranging from “virtually certain” (99–100%) to “exceptionally unlikely” (0–1%). These scales are applied to specific findings: the climate’s sensitivity to a doubling of CO₂, the contribution of ice sheet melting to sea-level rise, and the future frequency of extreme events. The conclusion that human influence on the climate system is “unequivocal,” as stated in the AR6 WGI Summary for Policymakers, falls outside the probability scale: it describes a fact directly observable from the data, not a projection.
Scientific skepticism has a specific meaning: it is the stance that requires verifiable evidence before accepting a claim, that applies the principle of falsifiability, and that revises conclusions in light of new data. A scientist who challenges a specific estimate of climate sensitivity by citing an alternative measurement method is exercising scientific skepticism. Someone who denies human influence on the climate—in contrast to the converging evidence from decades of observations and thousands of studies—is taking a different position. The documented problem is that in public discourse, these two positions are described using the same terms, producing two simultaneous effects: those who challenge specific estimates with methodological arguments are equated with systematic denial; those who systematically deny the influence of human activity can claim the epistemic legitimacy of “scientific skepticism.”
A doctor who seeks a second opinion before prescribing chemotherapy is exercising clinical caution. A patient who refuses to accept any diagnosis of cancer after four positive biopsies is taking a different stance. Calling both of these “questioning the diagnosis” places them in the same category, but they require opposite clinical responses.
The IPCC has formalized its uncertainty scales precisely to make this distinction operational in scientific communication. A statement classified as “virtually certain” (99–100%) is not in the same epistemic position as a statement with “medium confidence” regarding a specific parameter. Public discourse rarely makes this distinction. Instead, it uses a binary framework: those who challenge climate policy are labeled “deniers,” while those who support it are labeled “alarmists,” regardless of the specific issue being discussed or the degree of certainty with which the IPCC has classified it. The IPCC scale exists to prevent this oversimplification: not all climate uncertainties are equivalent, and not all challenges are of the same type.
The double standard has been a recurring theme in the Italian debate in recent years. On the one hand, those who express reservations about specific scenarios, projection methodologies, or the effectiveness of individual measures are sometimes equated, in public discourse, with those who deny the basic facts of climate change. On the other hand, those who wish to delay or limit climate policies may present themselves as voicing “scientific doubt” regarding findings that the IPCC classifies as having high or very high confidence. The 2019 petition is a documented example of the second mechanism. The difficulty of distinguishing it from the first—in the absence of a reference to the specific confidence scale—is part of the mechanism itself.
It must be acknowledged that the distinction between systematic denial and methodological skepticism is not always clear-cut. There are intermediate positions, scientifically unresolved questions, and areas where consensus is still emerging. Methodological skepticism is epistemically necessary: without it, science cannot correct itself. The history of climate science demonstrates this: some initial estimates of climate sensitivity have been revised, some scenarios reformulated, and some measurement methods replaced by more accurate ones. The documented problem is not that doubt is wrong: it is that “doubt,” “skepticism,” and “denial” are used as synonyms in public discourse, making it difficult to distinguish between challenging a specific parameter—where scientific debate is legitimate—and denying established findings—where the controversy is political.
This column explores climate-related terms whose technical meanings differ from their common perceptions. ““Skepticism,” “denial,” and “doubt” introduce a new dynamic: not a technical term that loses precision, but a continuous spectrum of epistemic positions that, in public discourse, is compressed into a dichotomy, simultaneously producing two opposing effects on the positions at either end of the spectrum.
The next time you read “scientific skepticism” or “denialism” in an article or political statement, there’s one question to ask: Which specific finding is being contested, and with what level of confidence had the IPCC classified it? If the finding has a high or very high level of confidence and the challenge does not cite a specific alternative method, the word “skepticism” is not describing an epistemic position.
