====== Climate Science - Scientific Consensus ====== **Page type:** Consensus | **Domain:** Climate Science | **Status:** Broad consensus on core physical claims; active expert disagreement on magnitude, timing, and policy implications --- ===== Lede ===== Within the climate science research community, broad consensus exists on several core physical claims: that Earth's average surface temperature has increased over the industrial era, that atmospheric concentrations of CO2 and other greenhouse gases have risen substantially since the mid-18th century, and that human activity - primarily fossil fuel combustion and land-use change - is the dominant cause of observed warming since roughly 1950. This consensus reflects independently-arrived-at agreement across research groups in multiple countries with varied funding sources, and is reflected in successive assessment reports by the Intergovernmental Panel on Climate Change (IPCC). Consensus is partial or absent on several related questions: the precise magnitude of climate sensitivity (how much warming results from a doubling of CO2), the probability and timing of threshold or tipping-point events, the reliability of regional projections, and the net economic and social consequences of projected warming. Expert disagreement is more pronounced - and crosses disciplinary lines - on questions of mitigation policy, adaptation strategy, and risk framing. Institutional endorsement by the EPA, the Royal Society, and similar bodies is noted here for context but is not itself treated as constituting consensus under this wiki's sourcing standards. Consensus is assessed from the underlying evidence and the degree of independent replication across research communities. --- ===== Evidence Base ===== ==== Surface Temperature Record ==== Multiple independent groups - including NASA's Goddard Institute for Space Studies, NOAA's National Centers for Environmental Information, the UK Met Office Hadley Centre, and the Berkeley Earth project - have reconstructed global mean surface temperature from overlapping but methodologically distinct instrumental records. These reconstructions agree that global average surface temperature rose by approximately 1.1-1.2 degrees C above the pre-industrial baseline (roughly 1850-1900) through the early 2020s, with most warming occurring after 1970.((IPCC, //Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change//, eds. V. Masson-Delmotte et al. (Cambridge: Cambridge University Press, 2021), SPM-5 to SPM-8.)) The degree of methodological independence across these reconstructions - different station networks, different interpolation methods, different sea-surface temperature datasets - strengthens the inference that the trend reflects a real signal rather than a shared artifact.((Zeke Hausfather, Kevin Cowtan, David C. Clarke, Peter Jacobs, Mark Richardson, and Robert Rohde, "Assessing Recent Warming Using Instrumentally Homogeneous Sea Surface Temperature Records," //Science Advances// 3, no. 1 (2017): e1601207.)) ==== Atmospheric CO2 and Greenhouse Forcing ==== Direct atmospheric measurements at Mauna Loa (continuous since 1958) and at other stations show CO2 concentration rising from approximately 315 ppm in 1958 to over 420 ppm by the early 2020s. Ice core records extend this to pre-industrial baselines of approximately 280 ppm.((Pieter Tans and Ralph Keeling, "Trends in Atmospheric Carbon Dioxide," NOAA Global Monitoring Laboratory, accessed 2024, https://gml.noaa.gov/ccgg/trends/.)) The physical mechanism by which CO2 and other greenhouse gases trap outgoing longwave radiation is established by laboratory spectroscopy and is not scientifically contested. Satellite measurements of outgoing radiation confirm that the wavelengths absorbed by CO2 show reduced emission to space, consistent with the predicted greenhouse effect.((J. E. Harries, H. E. Brindley, P. J. Sagoo, and R. J. Bantges, "Increases in Greenhouse Forcing Inferred from the Outgoing Longwave Radiation Spectra of the Earth in 1970 and 1997," //Nature// 410 (2001): 355-357.)) ==== Attribution of Observed Warming ==== Attribution science uses climate models, paleoclimate data, and physical reasoning to assess how much of observed warming can be explained by natural forcings (solar variability, volcanic eruptions) versus anthropogenic forcings. The IPCC Sixth Assessment Report (AR6, 2021) concluded that it is "unequivocal" that human influence has warmed the climate, and that human-caused warming likely accounts for approximately 1.07 degrees C of the observed ~1.1 degrees C rise - with natural forcings contributing negligibly to the trend over the same period.((IPCC, //Climate Change 2021: The Physical Science Basis//, SPM-7. The 1.07 degrees C figure carries a likely range of 0.8 degrees C-1.3 degrees C.)) Attribution rests on the detection of a "fingerprint" - a spatial and temporal pattern of warming (e.g., greater warming at night than day, greater warming at the poles, stratospheric cooling concurrent with tropospheric warming) that matches greenhouse gas forcing but not solar or volcanic forcing. Fingerprint-consistent signals have been detected across multiple climate variables and independently replicated across modeling groups.((Benjamin D. Santer et al., "Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes," //Science// 301, no. 5632 (2003): 479-483.))((Benjamin D. Santer et al., "A search for human influences on the thermal structure of the atmosphere," //Nature// 382 (1996): 39-46.)) ==== Survey Evidence on Researcher Agreement ==== Several studies have attempted to quantify the degree of agreement among publishing climate scientists on the anthropogenic warming claim. Cook et al. (2013) and Lynas et al. (2021) each reported agreement rates above 97% among peer-reviewed abstracts or papers that took a position on the question.((John Cook et al., "Quantifying the Consensus on Anthropogenic Global Warming in the Scientific Literature," //Environmental Research Letters// 8, no. 2 (2013): 024024.))((Mark Lynas, Benjamin Z. Houlton, and Simon Perry, "Greater Than 99% Consensus on Human Caused Climate Change in the Peer-Reviewed Scientific Literature," //Environmental Research Letters// 16, no. 11 (2021): 114005.)) These studies have been criticized methodologically - particularly for abstract-based coding, the exclusion of papers that took no position, and the framing of "97%" as a precise figure rather than a floor estimate. The criticisms do not overturn the finding of broad agreement but do argue that specific percentage claims warrant caution.((Richard S. J. Tol, "Quantifying the Consensus on Anthropogenic Global Warming in the Literature: A Re-analysis," //Energy Policy// 73 (2014): 701-705.)) --- ===== Limits and Open Questions ===== The existence of broad consensus on core attribution claims does not extend to several significant downstream questions. **Climate sensitivity.** Equilibrium climate sensitivity (ECS) - the warming expected from a sustained doubling of CO2 - remains a subject of active research. AR6 assessed ECS as "likely" between 2.5 degrees C and 4.0 degrees C, with a best estimate of 3.0 degrees C, narrowing somewhat from prior ranges. The tails of the distribution - particularly the probability of high sensitivity above 4.5 degrees C - remain disputed.((IPCC, //Climate Change 2021: The Physical Science Basis//, Chapter 7, 7-3 to 7-5.)) **Tipping points and nonlinearities.** Whether the climate system contains tipping elements - thresholds beyond which changes become self-sustaining and effectively irreversible (e.g., Greenland ice sheet destabilization, Amazon dieback, permafrost carbon release) - is an active area of research with genuine expert disagreement on both the existence of specific tipping points and the temperature thresholds at which they become relevant. Current estimates suggest multiple tipping elements may be at risk at warming levels between 1.5 degrees C and 2.0 degrees C above pre-industrial levels, but threshold estimates carry substantial uncertainty.((David I. Armstrong McKay et al., "Exceeding 1.5 degrees C global warming could trigger multiple climate tipping points," //Science// 377, no. 6611 (2022): eabn7950.))((Timothy M. Lenton et al., "Tipping Elements in the Earth's Climate System," //Proceedings of the National Academy of Sciences// 105, no. 6 (2008): 1786-1793.)) **Regional projections.** Global mean temperature projections carry substantially lower uncertainty than regional projections of precipitation, storm frequency, drought extent, and sea-level change. Confidence levels vary significantly by region and variable. **Economic and social impacts.** Integrated assessment models that translate physical climate projections into economic damages involve assumptions about discount rates, adaptation capacity, non-market harms, and distributional effects that are contested among economists, ethicists, and policy analysts - not merely between climate scientists and critics. These are not questions the physical science consensus settles. **Aerosol forcing.** The cooling effect of aerosol emissions (sulfur dioxide, black carbon, etc.) is the largest single source of uncertainty in attributing total radiative forcing, and has implications for both climate sensitivity estimates and projections of near-term warming. --- ===== Dissenting Viewpoints ===== The following viewpoint pages address positions that challenge, qualify, or offer alternative framings of the scientific consensus described above. Existence of a consensus does not render these viewpoints without merit; several involve genuine methodological disputes engaged with by researchers in the field. * [[climate-science-natural-variability-viewpoint]] - Arguments that natural climate variability accounts for a larger share of observed warming than the consensus attributes to it * [[climate-science-low-sensitivity-viewpoint]] - Arguments that equilibrium climate sensitivity lies at the lower end of assessed ranges, with implications for projected warming * [[climate-science-temperature-record-reliability-viewpoint]] - Critiques of the surface temperature record, including station siting, urban heat island adjustments, and homogenization methods * [[climate-science-attribution-methodology-viewpoint]] - Critiques of fingerprinting and detection-attribution methods used to establish human causation * [[climate-science-consensus-surveys-viewpoint]] - Critiques of the 97% consensus survey literature on methodological grounds * [[climate-science-benefits-of-co2-viewpoint]] - Arguments that elevated CO2 has net positive effects on plant growth and food production that are underweighted in impact assessments --- ===== Related Pages ===== * [[climate-science]] - Main topic * [[climate-science-history]] - History of climate science and the development of consensus * [[climate-change-policy-debate]] - Debate on mitigation and adaptation policy * [[climate-sensitivity-debate]] - Debate on equilibrium climate sensitivity * [[climate-change-economics-debate]] - Debate on economic modeling of climate impacts * [[ipcc-assessment-reports-history]] - History and methodology of IPCC assessment reports * [[epa-climate-endangerment-finding-controversy]] - Controversy over the EPA's 2009 Endangerment Finding * [[climate-change-tipping-points-debate]] - Debate on climate tipping points and threshold effects --- ===== Footnotes ===== ~~FOOTNOTES~~