Interchangeability of multi-decade skin and surface air temperature trends over land in models

Abstract

Satellite land surface temperature (Ts) records have now reached 20+ year length, but their trends may differ from historical records built from in-situ measurements of near-surface air temperature (Tas). In the ERA5 reanalysis, 60°S—60°N land Ts and Tas trends can differ by up to ±0.06 °C decade-1 over 20 years, depending on the period, or more on smaller spatial scales. Here I use 1979—1998 outputs from ACCESS1-0 climate model simulations with prescribed land Ts to understand changes in Ts and Tas. CO2’s effective radiative forcing (ERF) causes adjustments that warm Tas relative to Ts. In ACCESS1-0, vegetation enhances the adjustments to CO2 over land. Meanwhile, feedbacks in ACCESS1-0 oppose the adjustments, resulting in small long-term net effects on global temperature estimates. In coupled simulations from other models, there is no agreement on whether Ts or Tas warms more and the most extreme case shows global long-term differences of just 5 % between land Ts or land Tas trends. The results contrast with over-ocean behaviour where adjustments and feedbacks reinforce each other, and drive larger long-term Tas warming relative to Ts across all models.