GSAT changes are in 2081–2100 (SSP1-2.6 in b) relative to 1850–1900. The black curves show unconstrained projections, while the blue curves show projections constrained using the raw GSAT trend as a predictor. The red curves show projections constrained using the GSAT trend with ETP internal variability removed as a predictor (the scatter plot illustrating the PDF can be found in Extended Data Fig. 8). The corresponding 5–95% uncertainty ranges are shown by the horizonal lines with means shown as vertical tick marks. The orange lines show IPCC-assessed projections 33, 34. The grey lines show constrained projections from multivariate linear regression models, based on a set of climatological metrics derived from tropical and subtropical low-level cloud. Following Liang et al. 6, the first of these two cloud metrics is derived from the regression coefficient of monthly marine boundary layer cloud fraction against SST changes across the seasonal cycle averaged over the subtropics. The second cloud metric characterizes cloud shallowness defined by Brient et al. 10 based on the ratio of cloud fraction at levels below 900 hPa to that below 800 hPa over weakly subsiding tropics based on a climatology over the 1980–2005 period. The faint grey vertical line in b marks the 2 C global warming threshold of the Paris Agreement. Similar results relative to the base period 1995–2014 are shown in Extended Data Fig. 7.
