A NEW PERSPECTIVE ON RECENT GLOBAL WARMING - ASYMMETRIC TRENDS OF DAILY MAXIMUM AND MINIMUM TEMPERATURE

Monthly mean maximum and minimum temperatures for over 50% (10%) of th e Northern (Southern) Hemisphere landmass, accounting for 37% of the g lobal landmass, indicate that the rise of the minimum temperature has occurred at a rate three times that of the maximum temperature during the period 1951-90 (0.84-degrees-C versus 0.28-degrees-C). The decreas e of the diurnal temperature range is approximately equal to the incre ase of mean temperature. The asymmetry is detectable in all seasons an d in most of the regions studied. The decrease in the daily temperatur e range is partially related to increases in cloud cover. Furthermore, a large number of atmospheric and surface boundary conditions are sho wn to differentially affect the maximum and minimum temperature. Linka ges of the observed changes in the diurnal temperature range to large- scale climate forcings, such as anthropogenic increases in sulfate aer osols, greenhouse gases, or biomass burning (smoke), remain tentative. Nonetheless, the observed decrease of the diurnal temperature range i s clearly important, both scientifically and practically.