Discriminants of Twentieth-Century Changes in Earth Surface Temperatures
An approach to identifying climate changes is presented that does not hinge on simulations of natural climate variations or anthropogenic changes. Observed interdecadal climate variations are decomposed into several discriminants, mutually uncorrelated spatiotemporal components with a maximal ratio of interdecadal-to-intradecadal variance. The dominant discriminants of twentieth-century variations in surface temperature exhibit large-scale warming in which, particularly in the Northern Hemisphere summer months, localized cooling is embedded. The structure of the large-scale warming is consistent with expected effects of increases in greenhouse gas concentrations. The localized cooling, with maxima on scales of 1000–2000 km over East Asia, eastern Europe, and North America, is suggestive of radiative effects of anthropogenic sulfate aerosols.
© Copyright by American Meteorological Society 2001 (Manuscript received July 25, 2000, in final form August 18, 2000) T. Schneider was supported by a NASA Earth System Science Fellowship. We thank Keith Dixon for providing an ensemble of climate simulations with which we tested the analysis methods; Tom Delworth, Stephen Griffies, Tom Knutson, Paul Kushner, Thomas Müller, and Francis Zwiers for comments on drafts of this paper; and Heidi Swanson for editing the manuscript.