Simulation of the role of solar and orbital forcing on climate

The climate system is excited by changes in the solar forcing caused by two effects: (a) by variations of the solar radiation caused by dynamical processes within the Sun, and (b) by changes in the orbital parameters of the Earth around the Sun. Numerical simulations with a three-dimensional coupled ocean-atmosphere climate model have been performed to investigate the sensitivity of the climate system to both kinds of changes in the forcing. The climate system responds to the (relatively) short term variations of the solar output variations with changes in the surface temperature of up to 2 K, but without any noticeable long lasting effect. The response to the changes in the orbital parameters is more dramatic: dependent if the orbital parameters correspond to the Eemian (a warm phase at around 125 kyr BP) or the one at 115 kyr BP (the onset of the last ice age), the simulation produces a warm state or the initiation of a cold climate. For the Eemian, the simulated climate agrees with the temperature distribution derived from pollen data. For the glacial inception, the model gradually builds up a large snow cover in the northern part of North America. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.