COMPARISONS OF 2 METHODS OF REMOVING ANTHROPOGENICALLY RELATED VARIABILITY FROM THE NEAR-SURFACE OBSERVATIONAL TEMPERATURE-FIELD

Assessments of the veracity of model-generated variability are difficu lt because variability in observed climate data during the 20th centur y is composed of natural and anthropogenic (greenhouse gas and sulfate aerosol) factors in addition to internal climate fluctuations. Compar isons should be improved if some of these factors could either be extr acted from real world data or additions be made to model-generated var iability. Both options involve several assumptions, the most important of which is that the climate system is linear to a first approximatio n. We discuss this and other assumptions and present results from two different methods of removing variability related to anthropogenic fac tors using energy balance models (EBMs) and atmosphere/ocean general c irculation models (A/OGCMs). At a global scale, the pattern of the tre nd of surface temperature over the 1966-1995 period, after removing th e anthropogenic effect, shows some strong similarities between the two methods, with the strongest residual warming evident over much of nor thern Asia and northern North America.