Recent climate changes in the northwestern Qaidam Basin inferred from geothermal gradients

Abstract

Temperature perturbations under the ground surface are a direct thermal response to temperature changes on the ground surface. Thus, borehole temperature measurements can be used to reconstruct the temperature history of the ground surface using borehole Paleothermometry. In this study, we use seven borehole temperature profiles to reconstruct the ground surface temperature variation for the past 514 years in the Qaidam Basin, northwestern China. Borehole transient temperature measurements from seven sites in the northwestern Qaidam Basin were separated from the geothermal gradients and analyzed using the functional space inversion method to determine the ground surface temperature variation history of the region. All of the temperature profiles show the effects of recent climatic disturbances. The inversion reveals that during the last 514 years, the ground surface temperature has increased by an average of 1.2 °C (−0.11 to 2.21 °C). Clear signs of a cold period between 1500 and 1900 A.D. were found, which corresponds to the Little Ice Age. The coldest period occurred between 1780 and 1790 A.D. with a ground surface temperature of 5.4 °C. The reconstructed ground surface temperature shows an increasing trend during the 19th and the 20th centuries, but the temperature began to decrease in the late twentieth century. However, during the past 514 years, the highest temperature occurred in the 1990s. This reconstructed ground surface temperature variation history is verified by the simulated annual surface air temperature computed using EdGCM, while the cooling trend is confirmed by reconstructions of the winter half-year minimum temperatures from tree rings on the northeastern Tibetan Plateau.