Two Contrasting Views of Multidecadal Climate Variability in the 20th Century

Thursday, 18 December 2014
Anastasios Tsonis1, Sergey Kravtsov1, Marcia G Wyatt2 and Judith A Curry3, (1)University of Wisconsin Milwaukee, Milwaukee, WI, United States, (2)University of Colorado at Boulder, Boulder, CO, United States, (3)Georgia Tech-Earth & Atmos Sci, Atlanta, GA, United States
The bulk of our knowledge about causes of 20th century climate change comes from simulations using numerical models. In particular, these models seemingly reproduce the observed nonuniform global warming, with periods of faster warming in 1910–1940 and 1970–2000, and a pause in between. However, closer inspection reveals some differences between the observations and model simulations. Here we show that observed multidecadal variations of surface climate exhibited a coherent global-scale signal characterized by a pair of patterns, one of which evolved in sync with multidecadal swings of the global temperature, and the other in quadrature with them. In contrast, model simulations are dominated by the stationary — single pattern — forced signal somewhat reminiscent of the observed “in-sync” pattern most pronounced in the Pacific. While simulating well the amplitude of the largest-scale — Pacific and hemispheric — multidecadal variability in surface temperature, the model underestimates variability in the North Atlantic and atmospheric indices.