Modelling climatic change in South Africa from perturbed borehole temperature profiles

The climatic history over South Africa during the past few centuries is mod elled by mathematical inversion of perturbations in temperature profiles me asured in boreholes drilled in solid rock. Preliminary investigation reveal s that 19th and 20th century rapid warming of the ground surface commenced about 170 years ago and that on average surface temperatures have increased by 1.1 K since then in comparison to the 0.8 K rise observed in global air temperatures over land since the mid-18th century. Lowest temperatures der ived from the South African borehole temperature data set were reached arou nd 1790 in the last phase of the Little Ice Age when mean conditions were 0 .3 K cooler than in preceding centuries. The model is shown to have conside rable potential for determining regional magnitudes and gradients of climat ic change in the period before meteorological records. It may even be possi ble to resolve changes in climate earlier than the Little Ice Age in South Africa if temperature data from deep boreholes become available. (C) 1999 I NQUA/Elsevier Science Ltd. All rights reserved.