Long-term surface air temperature trend and the possible impact on historical warming in CMIP5 models

Abstract

Whether large trends exist in pre-industrial control (PICTL) runs is critically important for evaluating simulations of present climate change. This study examined the long-term trends in PICTL surface air temperature (SAT) in CMIP5 models. Small trends (<0.06 °C/100 year) in the globally averaged SAT (GASAT) exist in most CMIP5 models. Of these, positive (negative) trends result from positive (negative) net radiation fluxes at the TOA. This conclusion was further confirmed by the significant positive correlations between the TOA and the SAT tendency. The PICTL GASAT trends constitute less than 10% of the historical trends, indicating that such trends are of negligible importance in estimates of historical global warming in most models. Spatially, relative to the historical trends, the PICTL trends comprise a nontrivial fraction (>20%) in the Southern Ocean between 50°S and 65°S and in the northern Atlantic and Pacific oceans north of 40°N, with large inter-model spread. The long-term behavior of SAT is significantly related to ocean circulation adjustment in the mid–high latitudes.