from spatially and seasonally differentiated changes in climate as projected by AOGCMs. Again, while there is a relatively high degree of disagreement among models on the direction and magnitude of climate change, some salient patterns emerge from a systematic comparison of model projections. East Africa is expected to experience the highest absolute loss in cropland share due to a relatively high density of croplands today, whereas less densely cultivated areas will remain characterized by sparse cropping patterns despite positive changes at the margins. In general, the relative impact across the continent is highly differentiated and most pronounced in the tropical latitudes. Subtropical regions experience the least relative change due to positive perturbations in precipitation and temperature, respectively. Despite uncertainties in these estimates, the results make it clear that policy interventions in regard to land management, food policy, markets or poverty, intended to mitigate the impacts of climate change on agro-ecosystems, need to be tailored to each subregion, and that climate change needs to be considered when making long-term investments in agricultural infrastructure such as irrigation or the development of markets.

It is important to note that this analysis addresses only the impacts of changes in long-term average conditions of climate. However, there is a large body of evidence that shows that inter-annual variability in climate plays an important role for farmers’ risk management and livelihood strategies, crop choices and safety nets. In particular, shock-like events such as droughts, floods or storms can have detrimental effects on farmers’ welfare. Based on first order climate mechanisms, however, it is conceivable that patterns associated with these extreme events are likely to become more frequent with climate change (IPCC 2001) and may outweigh the effects of gradual changes in mean climate.

Ricardian analyses for Africa (Kurukulasuriya & Mendelsohn, 2006) suggest that agricultural productivity exhibits a negative or a U-shaped relationship with cropland density. That is, the marginal effect of increasing cropland does not result in higher land productivity in lowdensity systems, whereas in areas of higher cropping probability the effect is small or slightly positive. In other words, current land use is a reflection of cropping systems having adapted to normal conditions in the natural environment. Expansion of croplands as a result of more favorable climate is a meaningful policy only in productive agro-ecosystems, but will perpetuate low agricultural productivity and, by extension, poverty (Mendelsohn et al., 2004) in marginal cropping areas. Conversely, in productive agro-ecosystems trends towards less favorable climate can be compensated for to some extent by further cropland expansion. However, this policy raises issues of the opportunity costs associated with converting from non-cropping land uses (urban, forest, land conservation) to agriculture.

The results suggest significant changes of cropping patterns across the region, which are likely to have implications for food security, agricultural markets and trade. Population trends projected for Africa (United Nations 2004) are likely to exacerbate demand for crops unless increases in agricultural productivity can compensate for the loss of cultivable land. The analysis also shows that measurable changes in cropping patterns are likely to occur within the next several decades, which stresses the importance of institutions and land use policies in identifying and managing the impacts of climate change on agro-ecosystems in response to changes in climate. An important aspect of this is the creation of a system of incentives to facilitate the adaptation of agro-ecosystems to new conditions.

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