in the West Africa and the Sahel remain rather insignificant due to a sparse distribution of current croplands and low population density.

To further illustrate the range of impacts across the region, Figure 5 shows a geographic representation of results based on the SAGE cropland model and the NCAR, CCSR and CCC climate model (only the 2010–2039 period is shown). For reference, the actual and modeled distributions of croplands based on the SAGE model are depicted in the left and center panels in the top row, respectively, and the spatial patterns arising from an ensemble prediction of climate models are shown in the right panel in the top row. Figure 5 shows that despite differences in the model projections from various AOGCMs, general patterns of cropland sensitivity can be discerned. That is, while subtropical latitudes may experience increases in croplands at the margins due to relative increases in precipitations, eastern and northern Africa are likely to experience the highest relative and absolute losses in cropland area early in the century.

# **6. Conclusions and policy implications**

The objective of this analysis was to establish a quantitative relationship between land use in Africa and transient climate projections for the 21st century. The analysis presented here shows that current cropping patterns in Africa can be predicted reasonably well using a reduced set of geophysical variables including long-term seasonal temperature and precipitation and soil characteristics. To do this, spatially continuous representations of cropland share, climate and soil data were used to estimate the location specific sensitivities of current cropping patterns to perturbations in seasonal climate. Based on these sensitivities, a probabilistic and spatially differentiated estimate of the impact of climate change was calculated.

The first part of the analysis showed that despite significant discrepancies in alternative depictions of cropland share at the sub-regional level, the seasonal effects of precipitation and temperature changes are relatively consistent across models. However, because of differences in the geographic distribution of croplands, spatial sensitivity patterns vary considerably at finer spatial scales (e.g. at below-national levels) from model to model. Also, the projections of AOGCMs used here to characterize future climate have largely global to regional scope and need to be interpreted with caution at the sub-regional and local scale. The results presented here therefore highlight the patterns that emerge from a synthesis of an ensemble of cropland model regressions and climate model projections.

Geographically distinct patterns of climate sensitivity characterize different agro-ecological zones. Specifically, changes in precipitation in semi-arid and humid region have opposing effects, but the majority of the African continent has a unidirectional sensitivity to changes in temperature (with exceptions in some parts of southern and eastern Africa). This is consonant with the notion that increases in temperature tend to have negative effects on agriculture in tropical latitudes, and changes in precipitation largely affect the tail ends of precipitation regimes. It is important to note, however, that this analysis is concerned only with the allocation of land to cropping and does not consider climate impacts on crop yield and agricultural productivity.

While the first part of the analysis estimates the effect of uniform (and arbitrary) changes of climate across the region, the second part assesses the impact of cropland changes arising 12