Simulated difference in the mean annual number of heating degree days for the contiguous United States, for the 2041-2070 time period with respect to the reference period of 1980-2000 (top). Color with hatching (category 3) indicates that more than 50% of the models show a statistically significant change in the number of heating degree days, and more than 67% agree on the sign of the change (see text). Mean annual number of heating degree days for the 1980-2000 reference period (bottom left). Simulated mean annual number of heating degree days for the 2041-2070 future time period (bottom right). These are multi-model means from 8 NARCCAP regional climate simulations for the high (A2) emissions scenario. There are decreases everywhere with the largest changes in high elevation areas.