Comparison Between Doubled Co2 Time-Slice and Coupled Experiments

The production of climate simulations using global coupled ocean-atmosphere models at high resolution is currently limited by computational expense and the long periods of integration that are necessary. A method of increasing the number of experiments that can be performed is the so-called time-slice technique. Using the Arpege-climat atmospheric model three 5-yr integrations of this type were run: a control and two integrations forced with sea surface temperatures derived from coupled model simulations of the transient response to increasing carbon dioxide. These coupled models are the ECHAM1 model of the Max-Planck Institute (Hamburg, Germany) and the U.K. Meteorological Office model of the Hadley Centre. The sensitivity of the response to the oceanic forcing is studied. The results are compared with the 10-yr mean atmospheric response of the coupled models at the time of the doubling of CO2. Global warmings ranging from 1.3 K to 1.9 K are obtained. Special attention is given to the modifications that occur in the hydrological cycle and their sensitivity to the SSTs. Climatic signals related to oceanic forcing, such as the modification of the ITCZ maximum of precipitation, are separated from signals due to the internal feedbacks and physical parameterizations of the models.