# **_5.1 Ensemble projections of climate_**

The models used to evaluate the impact of climate change on cropland distributions in Africa for 2010–2099 are from (1) the Center for Climate Systems Research (CCSR) (Emori et al. 1999), (2) the Canadian Center for Climate Modeling and Analysis (CCC) (Boer, Flato & Ramsden 2000), (3) the Goddard Fluid Dynamics Laboratory (GFDL) (Delworth et al. 2002), (4) Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO) (Hirst et al. 1996), (5) the Hadley Center for Climate Prediction and Research (HCCPR) (Gordon et al. 2000), (6) the Max-Planck Institute for Meteorology (MPIM) (Roeckner et al. 1996), and (7) the National Center for Atmospheric Research (NCAR) (Washington et al. 2000). These models provide dynamic pathways of climate up to 2099 at a monthly time step and capture changes in the general patterns of atmospheric circulation as a result of increased greenhouse gases in the atmosphere. The model runs chosen for this analysis are based on the A2 emission scenario defined by the Intergovernmental Panel on Climate Change, which provides projections based on a very heterogeneous world with continuously increasing global population and regionally oriented economic growth that is relatively fragmented and slow (Nakicenovic & Swart 2000).

Long-term mean conditions of future climate were evaluated for three distinct periods (2010– 2039, 2040–69 and 2070–2099) and expressed as 30-year monthly means. The monthly predictions were seasonally adjusted in the same fashion as the historical 1961–2000 baseline record and resampled to the same grid resolution (0.5°). The resulting estimates were then used to predict changes in cropland share at the grid cell level.

For reference, changes in long-term seasonal precipitation and temperature for the 2010–2039 period are shown in Figure 3, and the respective agreement in the direction of change across seven AOGCMs is shown in Figure 4. The comparison shows that the models tend to agree on decreases in precipitation in the eastern and central part of the continent and a general increase in precipitation in subtropical latitudes (Figure 4). The largest increase in precipitation in these regions is projected for the summer and spring season (left hand panels in Figure 3), and projected decreases in precipitation are most significant in the equatorial coastal regions of the continent. For the winter and fall seasons, spatial patterns of precipitation change are less coherent.

Projected changes in surface temperature exhibit an equally non-uniform pattern, with the strongest temperature increase for the central and southern part of the continent during winter/spring and for the coastal areas in the southwestern and northern regions during summer/fall. The spatial patterns are less coherent in the central and eastern part of the continent throughout all seasons, and cooling is more likely in the high altitude regions of eastern and northeastern part of Africa (Figure 3). In general, the highest absolute changes in projected climate coincide with the regions of inter-model agreement and the seasons that exhibit a strong climate response, e.g. precipitation during the spring/summer and temperature during winter/spring (Figure 4).

Table 4 shows a breakdown of changes in mean annual precipitation and temperature for each 30-year period and each climate model in each sub-region (North: 20–38°N/10°W–40°E; West: 5–20°N/20°W–20°E; East: 20°N–15°S/30–50°E; Central: 5°N–15°S/8–30°E; and South: 15–35°S/20–50°E). Changes in temperature are given in °C and changes in precipitation in % relative to the 1961–2000 baseline. The table shows significant discrepancies across climate models. Specifically, while most models predict continuous warming across all regions for the entire time period, the CCC and NCAR model project a 10