The Influence of Changing Orbital Parameters and Surface Boundary Conditions on Climate Simulations for the Past 18 000 Years

Abstract

Abstract General circulation model experiments at 3000-year intervals for the past 18 000 years were made to estimate the magnitude, timing, and pattern of the climatic response to prescribed changes of orbital parameters (date of perihelion, axial tilt, eccentricity) and glacial-age lower boundary conditions (ice sheets, land albedo, sea ice and sea surface temperature). The experiments used the Community Climate Model (CCM) of the National Center for Atmospheric Research (NCAR). The response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial-age boundary conditions. The continental interior of Eurasia was 2–4 K warmer in summer, and summer monsoon precipitation of North Africa-South Asia was increased by 10–20% between 12 000 and 6000 yr BP (before present) when perihelion occurred during northern summer (rather than in winter as now) and the earth's axial tilt was larger than now. Southern Hemisphe...