CCSM SIMULATED CLIMATE AND VEGETATION FOR 6K NORTH AFRICA

The Community Climate System Model (CCSM) consists of four synchronously coupled components: atmosphere, ocean, sea ice, and land. The land model (Community Land Model) now includes a vegetation dynamics module with most routines from the Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM) of Sitch et al. (2003) and phenology adapted from the IBIS-DGVM (Kucharik et al. 2000). Three simulations are performed using the CCSM: (1) a present-day simulation (Control), (2) a 6000 year before present (6 kaBP) simulation with vegetation cover fixed at the present-day extent simulated in the Control (R), (3) a 6 kaBP simulation (RV). Present-day CO2 is set to 355 ppmv, while 6kaBP CO2 is set to 280 ppmv. CO2 for photosynthesis calculations only is kept at 355 ppmv in all three simulations, so CO2 fertilization of plants is not addressed here. Focusing on North Africa, simulation R shows an intensified monsoon compared to the Control. In simulation RV, grasslands expand northward and result in a positive feedback which intensifies the monsoon further. In particular, in the region from 15 to 25°N and 12°W to 34°E, July through September precipitation increases from 1.79 mm day-1 in the Control to 4.26 in R to 4.39 in RV. Previous coupled experiments (eg, Doherty et al. 2000) have shown similar results. Here we also show the trends in dust and biogenic volatile organic compound (BVOC) emissions in response to expanding grasslands. Annual dust emission decreases from 6 g dust m-2 day-1 in the Control to 5 in R to 4 in RV. Annual BVOC emission increases from 153 ugC m-2 day-1 in the Control to 434 in R to 1427 in RV. The CCSM does not yet simulate climate feedbacks due to these emissions. Inclusion of these feedbacks will add one more piece to the puzzle we call the Earth System.