Advanced Testing of Low, Medium, and High ECS CMIP6 GCM Simulations Versus ERA5-T2m

Abstract

The equilibrium climate sensitivity (ECS) of the CMIP6 global circulation models (GCMs) varies from 1.83°C to 5.67°C. Herein, 38 GCMs are grouped into three ECS classes (low, 1.80–3.00°C; medium, 3.01–4.50°C; high, 4.51–6.00°C) and compared against the ERA5-T2m records from 1980–1990 to 2011–2021. We found that all models with ECS > 3.0°C overestimate the observed global surface warming and that spatial t-statistics rejects the data-model agreement over 60% (using low-ECS GCMs) to 81% (using high-ECS GCMs) of the Earth's surface. Thus, the high and medium-ECS GCMs are unfit for prediction purposes. The low-ECS GCMs are not fully satisfactory yet, but they are also found unalarming because by 2050 they predict a moderate warming (ΔTpreindustrial→2050 ≲ 2°C).