Global Observed Changes in Temperature Extremes

Abstract:

We investigate changes in temperature extremes based on global gridded datasets of temperature observations covering the second half of the 20st and first decade of the 21^st centuries. These datasets include grids of annual extremes indices to investigate changes in frequency, intensity and duration of extreme temperature events, and daily temperature grids to relate the changes in extremes to changes in the distribution function.

Results show widespread and consistent changes in temperature extremes indices that are consistent with warming and include more frequent occurrence of warm days and nights, increased maximum temperatures and longer warm spell duration, for example. Similarly, observations show general changes towards less frequent and less intense cold extremes. These changes are consistent across multiple observational datasets including reanalyses.

Empirical probability distributions of daily maximum and daily minimum temperatures show significant shifts towards warmer conditions in almost all regions of the globe with sufficient observational coverage and globally. These shifts are stronger for daily minimum (i.e., night-time) temperatures. Changes in variance differ between regions but are generally not significant locally and no variance changes can be detected in the global distributions. Large regions show slight increases in skewness. In summary, shifts in the mean temperatures appear to be the dominant contribution to increased occurrence of hot extremes globally, while changes in higher statistical moments are less clear.