Extreme temperatures expected to change more quickly than average temperature     

When assessing the consequences of climate change for human health and most ecosystems, very high temperatures are much more important than average temperatures. Earlier studies have shown that cold extremes will warm faster than warm extremes and that warm extremes will warm faster than average temperatures. European scientists have published a study focused on extremely high air temperatures, represented by the 100-year return temperature (T₁₀₀). (T₁₀₀ is a specific statistical expression that means that every year you have a 1% chance of getting that temperature.) Their results show a projected global-mean temperature increase of 3.5°K by 2100, which is at the upper end of the range given by the models analyzed in the 2007 IPCC-AR4. The authors acknowledge that the present generation of climate models, including the one used in this study, tends to overestimate extreme temperature values. However, even after correcting for this bias, they found that by 2090-2100, projected T₁₀₀ far exceeds 40°C in Southern Europe and the U.S. Midwest and even reaches 50°C in large parts of the area equatorward of 30°, notably in India and the middle East, and also in most of Australia. The projected T₁₀₀ values, the authors note, should be taken seriously, since they indicate that potential for dangerously high future temperatures in densely populated areas.

Source: Sterl, A., C. Severijns, H. Dijkstra, W. Hazeleger, G. Jan van Oldenborgh, M. van den Broeke, G. Burgers, B. van den Hurk, P. J. van Leeuwen and P. van Velthoven, 2008. When can we expect extremely high surface temperatures? Geophysical Research Letters, vol. 35, L14703, doi:10.1029/2008GL034071, 5pp.