Anthropogenic Forcing and Decadal Climate Variability in Sensitivity Experiments of Twentieth- and Twenty-First-Century Climate

A methodology is formulated to evaluate the possible changes in decadal-timescale (10‐20-yr period) surface temperature variability and associated low-frequency fluctuations of anthropogenic forcing and changes in climate base state due to the forcing in simulations of twentieth- and twenty-first-century climate in a global coupled climate model without flux adjustment. The two climate change experiments both start in the year 1900. The first uses greenhouse gas radiative forcing (represented by equivalent CO2) observed during the twentieth century, and extends greenhouse gas forcing to the year 2035 by increasing CO2 1% yr21 compound after 1990 (CO2only experiment). The second includes the same greenhouse gas forcing as the first, but adds the effects of timevarying geographic distributions of monthly sulfate aerosol radiative forcing represented by a change in surface albedo (CO2 1 sulfates experiment). The climate change experiments are compared with a 135-yr control experiment with no change in external forcing. Climate system responses in the CO 2-only and CO2 1 sulfates experiments in this particular model are marked not only by greater warming at high latitudes in the winter

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