Global observed changes in extremes of temperature and precipitation 

Lisa Alexander
Hadley Centre for Climate Prediction and Research
Exeter, UK.

Through the coordination of the joint World Meteorological Organization Commission for Climatology (CCl) / World Climate Research Programme (WCRP) project  on Climate Variability and Predictability (CLIVAR) Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI), a suite of climate change indices derived from daily data were calculated which primarily focus on extremes.  By setting an exact formula for each index and using specially designed software, analyses done in different countries or different regions can fit together seamlessly.  Here we present the results from a number of ETCCDMI-coordinated workshops held in data sparse regions combined with high quality station data supplied by numerous international scientists to provide a previously unseen global picture of the patterns of trends in temperature and precipitation extremes.  Seasonal and annual indices obtained from daily station data were gridded using an angular distance weighting technique and trends in the gridded fields were tested for significance.  Results showed large scale significant changes in temperature extremes, especially from those indices derived from daily minimum temperature.  Over large parts of the globe the occurrence of warm nights has significantly increased by more than 50% with some regions experiencing a more than doubling of these extremes.  This contrasts with a similar reduction in the trends of cool nights implying a shift in the distribution of global minimum temperature.  As expected, precipitation extremes did not have such large scale coherence but some indicators such as the annual trends in number of consecutive wet days and dry days and trends in heavy and very heavy precipitation were remarkably coherent over large areas.  We believe that this is the most comprehensive study to date of global climate extremes.