Climate of the Past | 2021
Mid-Pliocene West African Monsoon rainfall as simulated in the PlioMIP2 ensemble
Abstract
Abstract. The mid-Pliocene warm period (mPWP; ∼3.2\xa0million\xa0years ago) is seen as the most recent time period characterized by a\nwarm climate state, with similar to modern geography and ∼400\u2009ppmv atmospheric CO2 concentration, and is therefore often considered\nan interesting analogue for near-future climate projections.\nPaleoenvironmental reconstructions indicate higher surface temperatures,\ndecreasing tropical deserts, and a more humid climate in West Africa\ncharacterized by a strengthened West African Monsoon (WAM). Using model\nresults from the second phase of the Pliocene Modelling Intercomparison\nProject (PlioMIP2) ensemble, we analyse changes of the WAM rainfall during\nthe mPWP by comparing them with the control simulations for the pre-industrial\nperiod. The ensemble shows a robust increase in the summer rainfall over\nWest Africa and the Sahara region, with an average increase of 2.5\u2009mm/d,\ncontrasted by a rainfall decrease over the equatorial Atlantic. An anomalous\nwarming of the Sahara and deepening of the Saharan Heat Low, seen in\n>90\u2009% of the models, leads to a strengthening of the WAM and\nan increased monsoonal flow into the continent. A similar warming of the\nSahara is seen in future projections using both phase 3 and 5 of the\nCoupled Model Intercomparison Project (CMIP3 and CMIP5). Though previous\nstudies of future projections indicate a west–east drying–wetting contrast\nover the Sahel, PlioMIP2 simulations indicate a uniform rainfall increase in\nthat region in warm climates characterized by increasing greenhouse gas\nforcing. We note that this effect will further depend on the long-term\nresponse of the vegetation to the CO2 forcing.\n