An Assessment of Earth's Climate Sensitivity Using Multiple Lines of Evidence
By S. Sherwood, M. Webb, J. Annan, K. Armour, Piers M. Forster, J. Hargreaves, Gabriele C. Hegerl, Stephen A. Klein, K. Marvel, E. Rohling and 15 more. Reviews of Geophysics, 2020
853 citations recorded by the source corpus.
We assess evidence relevant to Earth's equilibrium climate sensitivity per doubling of atmospheric CO2, characterized by an effective sensitivity S. This evidence includes feedback process understanding, the historical climate record, and the paleoclimate record. An S value lower than 2 K is difficult to reconcile with any of the three lines of evidence. The amount of cooling during the Last Glacial Maximum provides strong evidence against values of S greater than 4.5 K. Other lines of evidence in combination also show that this is relatively unlikely. We use a Bayesian approach to produce a probability density function (PDF) for S given all the evidence, including tests of robustness to difficult‐to‐quantify uncertainties and different priors. The 66% range is 2.6–3.9 K for our Baseline calculation and remains within 2.3–4.5 K under the robustness tests; corresponding 5–95% ranges are 2.3–4.7 K, bounded by 2.0–5.7 K (although such high‐confidence ranges should be regarded more cautiously). This indicates a stronger constraint on S than reported in past assessments, by lifting the low end of the range. This narrowing occurs because the three lines of evidence agree and are judged to be largely independent and because of greater confidence in understanding feedback processes and in combining evidence. We identify promising avenues for further narrowing the range in S, in particular using comprehensive models and process understanding to address limitations in the traditional forcing‐feedback paradigm for interpreting past changes.
Subfields: Atmospheric Science, Global and Planetary Change
View Paper: https://www.semanticscholar.org/paper/05c658043efb5934eb092aba9d53f5403a491e53
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Citations in the corpus
- Opinion: Cloud-phase climate feedback and the importance of ice-nucleating particles (2020, background): “Whether these high ECS values (Gettelman et al., 2019; Zelinka et al., 2020; Bodas-Salcedo et al., 2019) are possible or probable is a matter of debate (Palmer, 2020; Forster et al., 2020; Sherwood et al., 2020).”
- Reduced global warming from CMIP6 projections when weighting models by performance and independence (2020, background): “Compared with the unweighted case, these results clearly show that the CMIP6 models that lead to the highest warming are less probable, confirming earlier studies (e.g., Nijsse et al., 2020; Sherwood et al., 2020; Tokarska et al., 2020).”