GLOBAL WARMING AND GEOTHERMAL PROFILES - THE SURFACE ROCK-TEMPERATURERESPONSE IN SOUTH-AFRICA

Southern hemisphere and South African regional air temperature anomali es for the period 1860-1996 are compared to borehole-derived surface r ock-temperature anomalies to assess the extent to which surface rock t emperatures reflect possible global warming in South Africa. The warmi ng of the southern hemisphere since the mid-nineteenth century is evid ent in the regional air temperatures for South Africa. Following a tem perature increase to a maximum in the 1920s, the climate cooled until strong warning recommenced in the mid 1970s. Highest temperatures have been experienced in the 1990s. Borehole-derived surface rock temperat ures followed a similar pattern, but with a lag of a few decades in th e case of the 1920s maximum. The overall warming trend is clearly evid ent in the rock temperatures. Despite uncertainties in the different d ata sets, an encouraging degree of agreement exists between the increa se in rock temperatures during the twentieth century the corresponding regional South African air temperature increase and the southern hemi sphere counterpart.