Group members preparing summary: Francis, Amanda, Heather, and JesseClimate change is expected to impact agricultural production both positively and negatively. The impact and its severity remain uncertain due to uncertainties in the degree of temperature increase and its geographic distribution, likely concomitant precipitation pattern changes and the physiological response of crops to enriched carbon dioxide in the atmosphere. Understanding the agro-ecosystems and what happens when any one of its elements is changed will determine the appropriate societal responses. Results from controlled environments such as growth chambers and greenhouses suggest that CO2 increase may benefit C3 crops but C4 are less responsive to enriched concentrations. Overall however, other climatic changes such as severe droughts may negate such benefits of increased yields from C3 crops.
Warm temperatures may expand crop producing lands but crops that have become adapted to the growing-season day lengths of the middle and lower latitudes and may not respond well to the much longer days of the high latitude summers. Less than optimal conditions for net growth are more likely in warmer lower latitude regions.
The occurrence of moisture stress during flowering, pollination, and grain filling is harmful to most crops and particularly so to corn, soybeans, and wheat. Increased evaporation from the soil and accelerated transpiration in the plants themselves will cause moisture stress; as a result there will be a need to develop crop varieties with greater drought tolerance. Peak irrigation demands are also predicted to rise due to more severe heat waves. Additional investment for dams, reservoirs, canals, wells, pumps, and piping may be needed to develop irrigation networks in new locations. Finally, intensified evaporation will increase the hazard of salt accumulation in the soil. Frequent droughts not only reduce water supplies but also increase the amount of water needed for plant transpiration. Higher air temperatures will also be felt in the soil, where warmer conditions are likely to speed the natural decomposition of organic matter and to increase the rates of other soil processes that affect fertility.
Longer growing seasons and warm winter will enable insect pests to complete a greater number of reproductive cycles and also allow larvae to winter-over in new areas and cause greater infestation during the following crop season. Altered wind patterns may change the spread of both wind-borne pests and of the bacteria and fungi that are the agents of crop disease. Agriculture in low- lying coastal areas, where impeded drainage of surface water and of groundwater, as well as intrusion of seawater into estuaries and aquifers, might take place would be threatened by sea-level rise. Adaptations may come in the form of switching crop varieties, introduction of irrigation high-efficiency irrigation which may involve major investments. Another way would be to breed heat- and drought-resistant crop varieties by utilizing genetic resources that may be better adapted to new climatic and atmospheric conditions. Genetic manipulation may also help to exploit the beneficial effects of CO2 enhancement on crop growth and water use. Adaptation may not be easy as for example, where major shifts in crops needs to be made. Grain farmers may find themselves more exposed to marketing problems and credit crises brought on by higher capital and operating costs of fruit and vegetable production.
Africa, right on the edge of the worldīs largest, driest desert, the Sahara, there is a large freshwater lake, Lake Chad. This is a great example of effects on an area due to agricultural use. Lake Chad was once the sixth-largest lake in the world, but constant drought since the 1960īs has shrunk it to 1/10 its size. The Chari River, at the southeast, which provides 90% of Lake Chadīs water, now averages only about half of its original 40 billion cubic meters per year in the 1930-60s. The recent low levels are a concern, and have been monitored through satellite and other means by the Lake Chad Basin Commission and others.
People around Lake Chad are among Africaīs most chronically vulnerable to food insecurity. They have dealt with variability through mobility and through diversity of food sources. People who raise livestock typically moved closer to the lake for grass in the dry season, then move up to 100 km away in the rainy, mosquito season. After the 1970s droughts, herders shifted from grazing animals (cattle and camels) to browsing animals (sheep and goats), which affected the areaīs vegetation by consuming the woody plants. 8 Crop strategies have included farming the lake bottom and on "recessional lands", where the lake water recedes every year, in the "polder" depressions between dunes. In a traditional polder, one crop a year is grown as the lake water recedes. If dams and pumps are used, up to three crops a year can be grown. The potential impacts of increases droughts in the Lake Chad region would lead to further land degradation from browsing animals and the shorter shoreline from receding lake implies fewer polders to grow crops. Furthermore a low lake also means fewer fish, which may lead to an increase in other lake-related activities such as soda mining.