demand for cereal crops can be expected to rise by about 25% over the same period. {5.1}

Up to roughly 2ºC global warming, studies suggest that crop yield gains and adaptation measures (especially in higher latitude areas) could balance yield losses in tropical and other regions, but warming above 2ºC is likely to increase global food prices. Major increases in trade of food from temperate to tropical areas are expected as a result of warming and represent one form of adaptation. Temperate growers are also likely to shift to earlier planting and longer maturing varieties as climate warms. However, adaptations are expected to be less effective in tropical regions where soil moisture, rather than cold temperatures, limits the length of the growing season. Very few studies have considered the evidence for ongoing adaptations to existing climate trends and have quantified the benefits of these adaptations. Future development of new varieties that perform well in hot and dry conditions may also promote adaptation, but the extent to which this will be effective remains unclear. At the higher warming scenarios considered in this report, it will be increasingly difficult to generate varieties with a physiology that can withstand extreme heat and drought while still being economically productive. Without adaptation, studies suggest that food prices could more than double if global warming were to be 5ºC. These estimates do not include additional losses due to weeds, insects, and pathogens, changes in water resources available for irrigation, effects of increased flood or drought frequencies, or responses to temperature extremes. {5.1}

Global warming of 2ºC would be expected to lead to average yield losses of U.S. corn of roughly 25% (±16% very likely range) unless effective adaptation measures are discovered and implemented. Nearly 40% of global corn production occurs in the United States, much of which is exported to other nations. The future yield of U.S. corn is therefore important for nearly all aspects of domestic and international agriculture. Higher temperatures speed development of corn and increase soil evaporation rates; further warming above 35ºC can compromise pollen viability, all of which reduce final yields. A major challenge in developing drought- and heat-tolerant varieties is that traits that confer these attributes often reduce yields in good years. {5.1}

Fire

Wildfire frequency and extent is expected to change in many countries as the global average temperature increases. Site-specific studies suggest that large increases in the area burned are expected in parts of Australia,



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