CMIP6 GCM ensemble members versus global surface temperatures

Abstract The Coupled Model Intercomparison Project (phase 6) (CMIP6) global circulation models (GCMs) predict equilibrium climate sensitivity (ECS) values ranging between 1.8 and 5.7 $${^\circ }$$ ∘ C. To narrow this range, we group 38 GCMs into low, medium high ECS subgroups test their accuracy precision in hindcasting the mean surface warming observed from 1980–1990 to 2011–2021 ERA5-T2m, HadCRUT5, GISTEMP v4, NOAAGlobTemp v5 temperature records. We also compare GCM hindcasts satellite-based UAH-MSU v6 lower troposphere record. use 143 ensemble averaged simulations under four slightly different forcing conditions, 688 member simulations, Monte Carlo modeling of internal variability three model requirements. found that high-ECS run too hot up over 95% 97% cases, respectively. low agrees best with obtained records, 0.52 0.58 However, when comparing hindcasted on land ocean regions, surface-based records appear exhibit a significant bias. Furthermore, if UAH-MSU-lt record is accurate, actual 1980 2021 may have been around 0.40 C (or less), about 30% less than what reported by latter situation implies even low-ECS would produced excessive 2021. These results suggest be relatively i.e. 3 or 2 1980–2021 contain spurious warming, as some alternative studies already suggested. Therefore, projected next few decades could moderate probably not particularly alarming.