Implications of increasing carbon dioxide and climate change for agricultural productivity and water resources

Green plants need CO2 to grow. A higher concentration of atmospheric CO2 will stimulate the photosynthetic process, promoting plant growth and agricultural productivity without increasing the water demand for crop transpiration. On the otherhand, expected climatic warming may have adverse effects on agriculture, partly offsetting the positive direct CO2 effects. The availability of water resources depends on precipitation and potential evaporation, but also on many other factors. Interannual variability cannot be used to extract information of the impact of gradual climatic change. About 5 to 10% of the actual rate of increase of agricultural productivity worldwide can be ascribed to the fertilizing effect of rising atmospheric CO2. Thepositive direct effect of CO2 on plant growth is often smaller when crops are poorly fertilized, but it is fully retained when water shortage limits productivity. Beneficial and detrimental effects of climatic change will not be evenly distributed over the world. Cool and temperate climatic zones will benefit, but in the tropics a further increase in temperature will be undesirable. These changes will exert their influence at such a slow rate that they will be hardly noticeable compared with changes in technology and in economy. Yet they will gradually affect the range of options available.