ABSTRACT
The increased atmospheric carbon dioxide (CO2) concentrations can have a direct effect on the growth rate of crop plants and weeds. CO2-induced changes of climate may alter levels of temperature, rainfall and sunshine that can influence plant and animal productivity. CO2 is vital for photosynthesis, and the evidence is that increases in CO2 concentration would increase the rate of plant growth. The actual amount of increase in usable yield rather than of total plant matter that might occur as a result of increased photosynthetic rate is also problematic. In most of the tropical and equatorial regions of the world, and across large areas outside the tropics, the yield of agricultural crops is limited more by the amount of water received by and stored in the soil than by air temperature. Studies suggest that temperature increases may extend the geographic range of some insect pests currently limited by temperature.
