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Paleoclimate Modelling Intercomparison Project

Project Description
[Source: S. Joussaume and K. E. Taylor, proceedings of the third PMIP workshop, Canada, 4-8 october 1999, in WCRP-111, WMO/TD-1007, edited by P. Braconnot, 9-24, 2000. ]

Atmospheric general circulation models (AGCMs) are continually improving in their ability to simulate the major features of today´s climate. Many of these models are being used to predict future climate change and although there is broad agreement among the models, there are also many differences in the details of their predictions. In order to determine whether models can simulate climatic conditions much different from today, the models can be used to simulate paleoclimates, and paleodata can be used to evaluate the results. Moreover, AGCMs have proved their usefulness to investigate mechanisms of past climate changes (e.g., Joussaume, 1999)). The Paleoclimate Modeling Intercomparison Project (PMIP) was initiated in order to coordinate and encourage the systematic study of AGCMs and to assess their ability to simulate large changes of climate such as those that occurred in the distant past. It also is serving to encourage the preparation of global reconstructions of paleoclimates that can be used to evaluate climate models.

The PMIP effort developed out of a NATO Advanced Research Workshop, convened in 1991, which led to a cooperative and coordinated effort to compare model simulations with paleoclimate data. The workshop participants agreed to focus initially on two specific periods in the past : the last glacial maximum, 21 000 years before present (BP), and the mid-Holocene climate, 6 000 years BP, which correspond to extreme conditions that are relatively well documented. Simulating the last glacial maximum provides an opportunity for assessing the models´ ability to simulate extreme cold conditions as well as for studying the feedbacks associated with both a decrease of the atmospheric CO2 concentration and ice sheet elevation of 2 to 3 km above North America and northern Europe. The simulation of the mid-Holocene conditions is on the other hand a sensitivity experiment in which the seasonal contrast of incoming solar radiation at the top of the atmosphere is changed; 6000 years BP, the seasonal contrast was larger in the northern summer, leading to an increase of summer monsoons over Africa and South Asia.

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