Has There Been a Human Effect on Surface Air Temperature Extremes Regionally?

There is now a well established approach to detecting and attributing the causes of observed changes in mean climatic conditions that has been applied progressively from global scales to regional scales to temperature and other climate variables. While this research has provided a great deal of useful information about the causes of climate change observed during the past century or more, policy makers and others have also been demanding answers about whether there are attributable changes in frequency and/or intensity of extreme weather and climate events. We show that an anthropogenic influence is detectable globally, and in many regions, in the extremes of daily maximum and minimum temperatures. Globally, waiting times for extreme annual minimum daily minimum and daily maximum temperatures events that were expected to recur once every 20 years in the 1960s are now estimated to exceed 35 and 30 years respectively. .In contrast, waiting times for circa 1960s 20-year extremes of annual maximum daily minimum and daily maximum temperatures are estimated to have decreased to less than 10 and 15 years respectively.