Many scientists, economists, and policymakers agree that the world is facing a threat from climate warming (IPCC, 2001a). The degree of the impact and its distribution is still debated. The current evidence suggests that countries in temperate and polar locations may benefit from small economic advantages because additional warming will benefit their agricultural sectors (Mendelsohn et al., 2000; Mendelsohn and Williams, 2004). Many countries in tropical and subtropical regions are expected to be more vulnerable because additional warming will affect their marginal water balance and harm their agricultural sectors (IPCC, 2001b; Tol, 2002; Mendelsohn and Williams, 2004). However, little empirical research has been done on tropical countries, so that little is known about the extent of these damages. The problem is expected to be most severe in Africa, and especially sub-Saharan Africa, where the people are poor, temperatures are high, precipitation is low, technological change has been slow, and agriculture dominates domestic economies. African farmers have adapted to their current climates, but climate change may well force large regions of marginal agriculture out of production in Africa.
The agriculture sector is a major contributor to the current economy of most African countries. Across the continent, agriculture averages 21% of gross domestic product (GDP) but this value ranges from 10% to 70% of the GDP of individual countries (Mendelsohn et al., 2000).