Future Global Maize And Wheat Yields Negatively Affected By Climate-Warming Trends; Soy And Rice Yields Relatively Unaffected

Concerns about the stability of agricultural yields under the influence of warming climates cannot be addressed by policy-makers at the national level without information on likely future trends. With rising food prices and an expanding population, the strain on the global food supply is predicted to rise precipitously under the additional influence of global warming and its endemic temperature and precipitation changes. In an effort to identify the likely future effects of global warming on agricultural production, Lobell et al. (2011) utilized publicly available data in order to predict the likelihood and magnitude of changes in global agricultural yields due to climate change. By extrapolating data on yields and weather trends between 1980 and 2008, the team concluded that wheat and maize will experience lower yields much sooner than rice and soy, and that climate change is already decreasing yields globally for these grains.–Michael Gazeley-Romney
Lobell DB, Schlenker W, Costa-Roberts J. 2011. Climate trends and global crop production since 1980. Science 333: 616-620.

Lobell et al. compiled publicly available data on crop production, location, yields, growing season, monthly temperature (T) and precipitation (P) for past warming events and trends between 1980-2008 in order to extrapolate the magnitude of climate change’s effect on future global agricultural yields. Since maize (corn), wheat, rice, and soybeans represent roughly 75% of calories consumed by humans globally, the team identified the data sets for these four crops as having a greater share of global agricultural production and nutritional needs. The yield models were computed graphically on a world map to better illustrate national and regional trends. The researchers normalized temperature variations by applying the historical standard deviation of year-to-year fluctuations in temperature. Countries underwent warming trends of at least one standard deviation in growing regions for rice and maize 65% globally while 75% of rice and 53% of soybean regions experienced the same warming (except for the U.S. which experienced a cooling during the same period, and grows 40% of the net global maize and soy supply) while a quarter of countries experienced a shift of two standard deviations.
The authors used a regression model to infer relationships between the crops, climate change, and actual climate in the regions affected. For example, a 1°C° increase in temperature tended to lower yields by 10% except in high latitude countries, where warming is actually shown to increase rice gains. Results on the effect of precipitation were closely grouped across all four crops and all regions, except in time-specific instances of heavy rains where flooding greatly reduced the viability of the crop.
The authors took rising CO2 trends into account using data from an earlier study to adjust the effect of a changing atmosphere due to warming on the different crops.  The prior study had found that rising CO2 trends would likely raise production of C3 plant varieties like rice wheat and soybeans by 3%.  The yield models predicted global yield decrease of 3.8% for maize, 2.5% for wheat, but a 2.9% increase for rice, and 1.3% increase for soy. By dividing the climate induced yield change by the overall yield change the team posited that a decade of climate change would reverse the positive yield-growth effect of a year of technological advancements. Armed with a comparative measure of the yield impacts of climate change, the research team found maize and wheat to likely be exacting a heavy toll economically on a global scale due to their nutritional importance and regional susceptibility to temperature change.  By identifying the danger to the availability of two major food crops due to climate change, policymakers will be able to more accurately create contingencies to alleviate future pressure on the largest portion of global foodstuffs.

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