Global climate change, rated as the most serious threat to the environment, has been the center of debate among environmentalists and policy makers as it has become not only an environmental, a political and an economic issue, but also a global problem, of which agriculture is the major target. Therefore, the exponential growth of CO 2 and other greenhouse gasses in the atmosphere is causing climate change and it will be affected on agriculture, forestry, human health, biodiversity, snow cover and aquatic to mountain ecosystems. Changes in climatic factors like temperature, solar radiation and precipitation have potentials to influence crop production. Plants have been directly affected by rising atmospheric CO 2 concentration because they are the first molecular link between the atmosphere and the biosphere. The role of CO 2 in agriculture is complex in that it can be positive in some respects such as increasing [CO 2] will enhance photosynthesis and improve water use efficiency, thus increasing yield in most crops and negative in other respects. CO 2 concentration affects crop production directly by influencing the physiological processes of photosynthesis. The impact of increasing temperatures is more difficult to predict. Seed germination will probably be improved for most vegetables, as will vegetative growth in regions where mean daily temperatures during the growing season remain under 25°C, assuming adequate water is available. Reproductive growth is extremely vulnerable to periods of heat stress in many important vegetable fruiting crops, such as tomato, pepper, bean and sweet-corn, and yield reductions will probably occur unless production is shifted to cooler portions of the year. In many crops, high temperatures may decrease quality parameters, such as size, soluble solids and tenderness. For fresh-market vegetable producers, even minor quality flaws can make their crops completely unsaleable in some markets. Reduced or more irregular precipitation will also decrease vegetable yields and quality, although soluble solids and specific weight may increase in some crops. Leafy greens and most Cole crops such as broccoli, cabbage, cauliflower, are generally considered to be cool-season crops, so heat stress during the growing season would be detrimental to these species. Thus, planting dates, production areas and cultivars may need to be adjusted if temperatures change.
