Corn is a crop of tropical origin, so temperatures up to 100 or even 105 degrees are not detrimental, unless water is limited. If water is inadequate, water loss from leaves slows down, and the cooling effect of this water loss (similar to the cooling that people experience when sweat evaporates) decreases, so leaf temperatures can go up quickly in bright sunlight. Leaf death can result if this lasts long enough or if temperature is high enough. On balance, however, lower rainfall that is expected to accompany global warming in some areas is a bigger threat to the corn crop than increases in temperature.
Corn is what plant scientists call a “C4” crop, which refers to the way the crop takes in CO2 from the air. Such crops—sorghum and sugarcane are others—tend to produce high yields and to be very efficient in water use because of how they take up CO2. But because of this high efficiency, increasing the CO2 level in the air, which usually increases the yield of non-C4 crops such as soybean and wheat, is expected to have only a small effect on corn yield.
