Observed decadal mean seasonal temperature change

Observed decadal mean temperature change (deviations from the 1901-1960 average, F) for the Midwest U.S. for winter (top left, blue line), spring (top right, green line), summer (bottom left red line), and fall (bottom right, orange line). Based on a new gridded version of COOP data from the National Climatic Data Center, the CDDv2 data set (R. Vose, personal communication, July 27, 2012). Gray lines indicate 20th and 21st century simulations from 15 CMIP3 models, for the high (A2) emissions scenario. The observed amount of 20th century warming is within the envelope of model simulates in winter, spring, and fall, but it is less than model simulations in summer.