Empirical estimation of anthropogenic and natural contributions to surface air temperature trends at different latitudes

Abstract: How strong are quantitative contributions of the key natural modes of climate variability and the anthropogenic factor characterized by the changes of the radiative forcing of greenhouse gases in the atmosphere to the trends of the surface air temperature at different latitudes of the Northern and Southern Hemispheres on various time intervals? Such contributions to trends are estimated here from observation data with the simplest empirical models. Trivariate autoregressive models are fitted to the data since the 19th century and used to assess the impact of the anthropogenic forcing together with different natural climate modes including Atlantic Multidecadal Oscillation, El-Nino / Southern Oscillation, Interdecadal Pacific Oscillation, Pacific Decadal Oscillation, and Antarctic Oscillation. For relatively short intervals of the length of two or three decades, we note considerable contributions of the climate variability modes which are comparable to the contributions of the greenhouse gases and even exceed the latter. For longer intervals of about half a century and greater, the contributions of greenhouse gases dominate at all latitudes as follows from the present analysis of data for polar, middle and tropical regions.