Surface air temperature and its changes over the past 150 years

We review the surface air temperature record of the past 150 years, conside ring the homogeneity of the basic data and the standard errors of estimatio n of the average hemispheric and global estimates. We present global fields of surface temperature change over the two 20-year periods of greatest war ming this century, 1925-1944 and 1978-1997. Over these periods, global temp eratures rose by 0.37 degrees and 0.32 degrees C, respectively. The twentie th-century warming has been accompanied by a decrease in those areas of the world affected by exceptionally cool temperatures and to a lesser extent b y increases in areas affected by exceptionally warm temperatures. In recent decades there have been much greater increases in night minimum temperatur es than in day maximum temperatures, so that over 1950-1993 the diurnal tem perature range has decreased by 0.08 degrees C per decade. We discuss the r ecent divergence of surface and satellite temperature measurements of the l ower troposphere and consider the last 150 years in the context of the last millennium. We then provide a globally complete absolute surface air tempe rature climatology on a 1 degrees x 1 degrees grid. This is primarily based on data for 1961-1990. Extensive interpolation had to be undertaken over b oth polar regions and in a few other regions where basic data are scarce, b ut we believe the climatology is the most consistent and reliable of absolu te surface air temperature conditions over the world. The climatology indic ates that the annual average surface temperature of the world is 14.0 degre es C (14.6 degrees C in the Northern Hemisphere (NH) and 13.4 degrees C for the Southern Hemisphere). The annual cycle of global mean temperatures fol lows that of the land-dominated NH, with a maximum in July of 15.9 degrees C and a minimum in January of 12.2 degrees C.