Surface air temperature and its changes over the past 150 years

Abstract. We review the surface air temperature record of the past 150 years, considering the homogene-ity of the basic data and the standard errors of estima-tion of the average hemispheric and global estimates. We present global fields of surface temperature change over the two 20-year periods of greatest warming this century, 1925-1944 and 1978-1997. Over these periods, global temperatures rose by 0.37 ø and 0.32øC, respec-tively. The twentieth-century warming has been accom-panied by a decrease in those areas of the world affected by exceptionally cool temperatures and to a lesser extent by increases in areas affected by exceptionally warm temperatures. In recent decades there have been much greater increases in night minimum temperatures than in day maximum temperatures, so that over 1950-1993 the diurnal temperature range has decreased by 0.08øC per decade. We discuss the recent divergence of surface and satellite temperature measurements of the lower troposphere and consider the last 150 years in the con-text of the last millennium. We then provide a globally complete absolute surface air temperature climatology on a 1 ø x 1 ø grid. This is primarily based on data for 1961-1990. Extensive interpolation had to be under-taken over both polar regions and in a few other regions where basic data are scarce, but we believe the climatol-ogy is the most consistent and reliable of absolute sur-face air temperature conditions over the world. The climatology indicates that the annual average surface temperature of the world is 14.0øC (14.6øC in the North-ern Hemisphere (NH) and 13.4øC for the Southern Hemisphere). The annual cycle of global mean temper-atures follows that of the land-dominated NH, with a maximum in July of 15.9øC and a minimum in January of 12.2øC. 1