higher sensitivity to future increases in temperature than precipitation. Further, they find that doubling CO2, which leads to rises in temperatures by 2 _°_ C and precipitation by 7%, would have a negative impact on sugarcane production. They also find that irrigation in sugarcane production does not provide an effective option for reducing climate change damages in South Africa. Gbetibouo and Hassan (2005) also use the Ricardian approach to analyze the economic impact of climate change on major South African field crops. They find that crops are quite sensitive to marginal changes in temperature compared to changes in precipitation. Contrary to findings by Deressa et al. (2005), they argue that irrigation would be an effective adaptation measure for limiting the harmful effects of climate change, and that the impact of climate change is agro-ecological zone specific and therefore that location is important in dealing with climate change issues.

# **_4.3 Production function approach studies_**

Turpie et al. (2002) analyze the economic impact of climate change in South Africa. Their study addresses impacts on natural, agricultural, man-made and human capital. They use the production function approach to measure the natural capital lost from global warming. They predict the impact of climate change on rangelands will be positive, with the fertilization impact of CO2 outweighing the negative effects of reduced precipitation. However, they find the impact of climate change on maize production will be negative both ‘with’ and ‘without’ CO2 fertilization. They found estimates of impact of climate change for other crops were not reliable.

Other studies that use the production function approach argue that climate change may have beneficial effects on agriculture, especially in more arable lands, but adverse effects on more arid zones (for example Downing 1992). The positive impact of CO2 fertilization effects and rising temperatures may however be determined by the adaptation measures adopted by farmers. Studies that support this argument include Inglesis and Minguez (1997), Mohamed et al. (2002) and Schulze et al. (1993). Inglesis and Minguez (1997) report that with a combination of different adaptation strategies in Spain, farmers not only derived higher crop yields with increased temperatures but also used water and land more efficiently. Mohamed et al. (2002) argue that climate change factors are significant determinants of millet productivity in Niger and predict a huge fall in crop productivity by 2025 as a result of global warming. Downing (1992) argues that potential food production in Kenya will increased if increased temperatures are accompanied by high rainfall, while marginal zones will be adversely affected by decreased rainfall. Fischer and Velthuizen (1996) (as cited by Kurukulasuriya & Rosenthal 2003) note that food productivity in Kenya may well increase with higher levels of atmospheric CO2 and climate change induced increases in temperatures accompanied by some increases in precipitation, as predicted by several GCMs. These arguments are also supported by Makadho (1996), who argues that maize production in Zimbabwe is expected to fall as a result of increased temperatures that shorten the crop growth period. Downing (1992) also shows that shifts in agro-climate potential would affect national food production and land use in Zimbabwe.

Schulze et al. (1993) in a study of South Africa, Lesotho and Swaziland find climate change to be associated with potential increases in maize production, though they argue that it is likely to have little effect in marginal areas where yields are already low. Sivakumar (1992) in a study for Niger argues that climate has significant implications for agriculture because farmers tend to change their farming patterns with climate change and this is likely to have 15