48 | IAASTD Synthesis Report

(IPCC) Fourth Assessment Report moderate local increases in temperature (1-2°C) can have small beneficial impacts on crop yields. However, in low-latitude regions, even such moderate temperature increases are likely to have negative yield impacts for major cereals. Some negative impacts are already visible, especially in developing countries.  [ESAP Chapter 2; Global Chapter 5; NAE Chapter 3]. Further warming will have increasingly negative impacts, particu­larly affecting production in food insecure regions. Warm­ing in NAE will lead to a northward expansion of suitable cropping areas as well as a reduction of the growing period of crops such as cereals, but results, on the whole, project the potential for global food production to increase with increases in local average temperature over a range of 1 to 3°C, and above this range to decrease.
     From an ecosystem perspective, the rate of change can be more important. By 2030, temperature increases of more than 0.2 C° per decade are projected. Rates in excess of this are considered by some experts to be dangerous, al­though our current understanding is still uncertain [Global Chapter 5].
     Although   the   state   of  knowledge   of  precipitation changes is currently insufficient for confidence in the de­tails, we expect that for many crops water scarcity will increasingly constrain production. Climate change will re­quire a new look at water storage to cope with the impacts of changes in total amounts of precipitation and increased

 

rates of evapotranspiration, shifts in ratios between snow­fall and rainfall and the timing of water availability, and with the reduction of water stored in mountain glaciers. Many climate impact studies project global water problems in the near future unless appropriate action is taken to im­prove water management and increase water use efficiency. Projections suggest that by 2050 internal renewable water is estimated to increase in some developed countries, but is expected to decrease in most developing countries [Global Chapter 5].
     Climate change will increase heat and drought stress in many of the current breadbaskets in China, India, and the United States and even more so in the already stressed ar­eas of sub-Saharan Africa. Rainfed agriculture, especially of rice and wheat in the ESAP, is likely to be vulnerable. For example, rainfed rice yield could be reduced by 5-12% in China for a 2°C rise in temperature. [ESAP Chapter 4; Global Chapter 6; NAE Chapter 3].
     Most climate models indicate a strengthening of the summer monsoon and increased rainfall in Asia, but in semiarid areas in Africa the absolute amount of rain may decline, and seasonal and inter-annual variation increase. Reductions in the duration or changes in timing of the on­set of seasonal floods will affect the scheduling and extent of the cropping and growing seasons, which may in turn have large impacts on livelihoods and production systems. For example, droughts occurring in the monsoon period se-