Equilibrium Climate Sensitivity and Transient Climate Response biased
low in historical simulations of CMIP6 models
This study assesses the effective climate sensitivity (EffCS) and
transient climate response (TCR) derived from global energy budget
constraints within historical simulations of 8 CMIP6 global climate
models (GCMs). These calculations are enabled by use of the Radiative
Forcing Model Intercomparison Project (RFMIP) simulations, which permit
accurate quantification of the historical effective radiative forcing.
We find that long-term historical energy budget constraints generally
underestimate EffCS from CO2 quadrupling and TCR from CO2 ramping, both
by 12%, owing to changes in radiative feedbacks and changes in ocean
heat uptake efficiency. Atmospheric GCMs forced by observed warming
patterns produce lower values of EffCS that are more in line with those
inferred from observed historical energy budget constraints.
Understanding the discrepancies between modeled and observed historical
surface warming patterns remains critical for constraining EffCS and TCR
from the historical record.