DO 99% of scientists agree that climate change is caused by human activities? if not, what do 99% agree on, and where does that come from?
Executive summary
The short answer is: not always in the literal phrasing “99% of scientists,” because the precise percent depends on which study, which population (all scientists vs. climate specialists vs. peer‑reviewed papers) and which method is used, but the substantive finding across methods is unanimous in practice: an overwhelming majority of climate experts and the peer‑reviewed literature attribute recent warming primarily to human activities (IPCC and major science bodies), with common estimates ranging from about 97% of actively publishing climate scientists to studies of the literature that report >99% agreement [1] [2] [3].
1. Why the headline numbers differ: methods and populations
Consensus figures vary because researchers measure different things: surveys of individual scientists ask about beliefs and expertise while literature reviews code papers for endorsement of human‑caused warming, producing different numerators and denominators; for example, widely cited surveys and institutional summaries cite ~97% agreement among actively publishing climate scientists that humans are causing warming (NASA, IPCC summaries) whereas a 2021 literature survey of 88,125 climate‑related papers reported greater than 99% agreement in the peer‑reviewed literature [1] [2] [3].
2. What the largest, reputable studies actually find
Multiple independent efforts converge on a very high level of concordance: synthesis work repeatedly finds consensus estimates clustered around the high‑90s for climate specialists, and the IPCC’s assessment language — “unequivocal that human influence has warmed the atmosphere, ocean and land” — echoes that expert agreement [4] [5] [6]. The 2013 Cook et al. and follow‑up analyses placed the consensus near 97% for papers expressing a position, while later re‑analyses of larger corpora of abstracts and papers have pushed literature‑based estimates above 99% [7] [3].
3. Where the “97%” and “>99%” claims come from, exactly
The oft‑quoted 97% originates from several lines of work: surveys of publishing climate scientists and a synthesis paper that combined independent estimates (e.g., Cook et al., Doran & Zimmerman) which reported ~97% endorsement among those expressing a position; the >99% figure comes from later, larger literature‑coding efforts such as Lynas et al. , which analyzed tens of thousands of climate‑related papers and concluded that more than 99% of peer‑reviewed studies endorsed human causation [7] [3].
4. Where critiques and nuance matter
Critics caution about overstatement when the denominator expands beyond climate specialists: analyses that include broad groups of scientists or non‑publishing respondents sometimes find lower agreement (e.g., analyses suggesting 80–90% when including many specialties), and methodological choices — how “endorsement” is coded, whether neutral papers are excluded, and how expertise is weighted — materially affect headline percentages [8] [7]. Those critiques do not deny a strong consensus among qualified climate researchers; they argue precision and transparency in claims are important.
5. What virtually all consensus measures do agree on
Regardless of whether the exact number is 97%, 99%, or 99.9%, the consistent conclusion across surveys, literature reviews, and institutional assessments is that recent global warming is primarily caused by human activities — chiefly greenhouse‑gas emissions from burning fossil fuels — and that the consensus is robust enough that major scientific organizations and the IPCC treat it as settled science for policy and communication purposes [2] [5] [6].
6. Why the distinction matters for public discourse
Public perception underestimates this scientific agreement by a large margin, and research shows communicating the strength of the consensus increases belief in human‑caused climate change and concern for action; yet consensus messaging can be politicized and misrepresented, so accuracy about which number is cited (97% of active climate scientists vs. >99% of peer‑reviewed papers) matters for credibility and trust [9] [10] [11].