Implications of changes in the atmospheric circulation on the detection of regional surface air temperature trends

Abstract

Previous studies have shown that observed significant warming trends in surface air temperature (SAT) consistent with the response to anthropogenic forcing are detected at scales on the order of 500 km in many regions of the globe. However, regional SAT trends project strongly on the dominant natural atmospheric circulation modes, such as the Arctic Oscillation (AO) and the hemispheric Pacific-North America (PNA)-like patterns. The warming associated with the changes of atmospheric circulation is not well simulated in current coupled climate models. In this study, we explore the influence of the exclusion of warming related to changes of the atmospheric circulation on the detection of a regional response to combined anthropogenic and natural forcings. We compare observed SAT trends over the second half of the 20th century with those simulated in response to natural and anthropogenic climate forcings in a suite of six current coupled general circulation models. Control runs from these models are used to provide estimates of the internal variability of trends. We find that the detection of the regional response to combined anthropogenic and natural forcing is robust to the exclusion of warming related to changes of the atmospheric circulation considered here. Copyright 2007 by the American Geophysical Union.