Warmer daily temperatures since 1951



Days and nights have indeed become warmer over the past 60 years, a new study finds. Although several observation-based studies have shown that daily average temperatures as well as daily maximum and minimum temperatures have increased over the past few decades, controversy has remained as to how the observed trends in extreme and average temperatures are related to each other: Are the warming trends in extreme temperatures a result of a shifting mean climate, or have temperatures become more variable? Using a global observational data set of daily temperatures, Donat and Alexander compared the probability distributions of daily maximum and minimum temperatures over two 30-year periods, 1951–1980 and 1981–2010. The authors show that the maximum and minimum daily temperatures all over the globe have significantly shifted toward higher values during the latter period. They further show that the distributions have become skewed toward the hotter part of the distribution; changes are greater for daily minimum (nighttime) temperatures than for the daily maximum (daytime) temperatures. The authors conclude that the distribution of global daily temperatures has indeed become “more extreme” compared to the middle of the twentieth century. (Geophysical Research Letters, doi:10.1029/2012GL052459, 2012)