Climate change bad news for U.S. farmers, especially in Midwest
August 27th, 2009 by Jim JustThe American Midwest will suffer the most from climate change, according to a new analysis of U.S. climate projections from The Nature Conservancy.
Temperatures in the worst-hit U.S. states could be up to 10 degrees Fahrenheit hotter than present-day levels by the year 2100. Kansas, Nebraska and other Great Plains states would be the hardest-hit by climbing temperatures. But temperatures everywhere in the U.S. could rise by 3 degrees Fahrenheit or more.
In the agricultural states of the Great Plains, rising temperatures will cause shifts in the optimal zones for growing certain crops; milder winters and earlier springs will exacerbate outbreaks of insect pests; and water sources will become taxed as aquifers are depleted and soil moisture declines.
Another study by North Carolina State University agricultural and resource economists Dr. Michael Roberts and Dr. Wolfram Schlenker, published online this week in Proceedings of the National Academy of Sciences, predicts that U.S. crop yields could decrease by 30 to 46 percent over the next century under the most benign global warming scenarios and by a devastating 63 to 82 percent under the most rapid global warming scenarios.
The study shows that when temperature levels go over 29 degrees Celsius (84.2 degrees Fahrenheit) for corn, 30 degrees Celsius (86 degrees Fahrenheit) for soybeans and 32 degrees Celsius (89.6 degrees Fahrenheit) for cotton, yields fall steeply.
Co-author Roberts says:
While crop yields depend on a variety of factors, extreme heat is the best predictor of yields . . . this study shows that temperature extremes are not good.
While the study examined only U.S. crop yields under warming scenarios, the implications are ominous for the entire world.
Here’s the abstract:
The United States produces 41% of the world’s corn and 38% of the world’s soybeans. These crops comprise two of the four largest sources of caloric energy produced and are thus critical for world food supply. We pair a panel of county-level yields for these two crops, plus cotton (a warmer-weather crop), with a new fine-scale weather dataset that incorporates the whole distribution of temperatures within each day and across all days in the growing season. We find that yields increase with temperature up to 29° C for corn, 30° C for soybeans, and 32° C for cotton but that temperatures above these thresholds are very harmful. The slope of the decline above the optimum is significantly steeper than the incline below it. The same nonlinear and asymmetric relationship is found when we isolate either time-series or cross-sectional variations in temperatures and yields. This suggests limited historical adaptation of seed varieties or management practices to warmer temperatures because the cross-section includes farmers’ adaptations to warmer climates and the time-series does not. Holding current growing regions fixed, area-weighted average yields are predicted to decrease by 30-46% before the end of the century under the slowest (B1) warming scenario and decrease by 63-82% under the most rapid warming scenario (A1FI) under the Hadley III model.