CO 2/H 2O and orbitally driven climate variability over central Asia through the Holocene

Abstract

Small variations in Earth's orbit have a direct impact on global climate with the greatest changes occurring over large land masses such as Asia. Orbitally driven climate signals are therefore likely to be identifiable in climate proxy records derived from sediment sections in the continental interior. Proxy records derived from temperature-dependent variables are also likely to display a signal due to temporal variability of atmospheric CO 2 and related climatic parameters such as water vapour content. To determine the magnitude of climate anomalies associated with shortwave and longwave radiative forcing over Asia, a suite of numerical atmospheric simulations is performed that spans most of the Holocene (from 10,000 to 2500 years BP) at 500-year intervals. Over central Asia, the amplitude of the summer–winter seasonal cycle is greater than today in all simulations but exhibits two distinct maxima at 9000 and 6000 BP. Simulated precipitation and snow accumulation over central Asia are markedly higher during the early mid Holocene and are oscillatory, exhibiting peaks at 8000–7500 and 4500 BP (the Atlantic and Subboreal times, respectively). CO 2/H 2O forcing and orbital forcing combine to drive temperature oscillations over central Asia which, in turn, regulate relative humidity and changes in surface hydrology. Correlation between simulated results and proxy records from across Asia suggest that CO 2/H 2O and orbital forcing are dominant factors driving fluctuations of large-scale, central Asian climate through the Holocene.