Warming in the Heartland: Is the nation’s “breadbasket” toast?—Another preparedness challenge

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Yields of three of the most important crops produced in the United States – corn, soybeans, and cotton – are predicted to “fall off a cliff” if temperatures rise due to climate change, according to a paper published online this week in Proceedings of the National Academy of Sciences.  Global warming impacts on agricultural production should be included in the adaptation component of the Senate climate and clean energy bill—and estimates of potential CO2 “offsets” in the agricultural sector should factor-in the potential crop loss due to climate change-induced heat stress and drought.

Post by Anne Polansky

U.S. crop yields could decrease by 30 to 46 percent over the next century, as predicted by slow global warming scenarios used in a sophisticated computer model. But more rapid warming scenarios show much greater losses, between 63 to 82 percent, according to an online paper in Proceedings of the National Academy of Sciences. The work was described in a news release from North Carolina State University, home to one of the research scientists.

The study shows that crop yields tick up gradually with warming in the temperature range between roughly 10 and 30 degrees Celsius, or about 50 to 86 degrees Fahrenheit. But when temperature levels go over 29 degrees C (84.2 degrees F) for corn, 30 degrees C (86 degrees F) for soybeans, and 32 degrees C (89.6 degrees F) for cotton, yields fall steeply.

The research team used new weather data merged with crop-yield information from U.S. counties between 1950 and 2005.  The results have global implications, as the United States produces 41 percent of the world’s corn, and 38 percent of the world’s soybeans.

An abstract of the paper follows.

“Nonlinear temperature effects indicate severe damages to U.S. crop yields under climate change”

Authors: Wolfram Schlenker, Columbia University and Michael Roberts, North Carolina State University

Published: Aug. 24, 2009, in the online version of Proceedings of the National Academy of Sciences

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.

Cliimate Wire (by subscription) picked up the story today:  “Big U.S. cash crops could decline by 80% from heat”

Three of the biggest cash crops in the United States could decline by as much as 80 percent over the next century because of climate change, a new study finds.
The magic number for the destruction of corn, soybeans and cotton is 86 degrees Fahrenheit, researchers from two universities discovered. Both the number of days and the number of degrees that these crops bake in the sun over that temperature threshold are equally destructive. ….“Ten days with 1 degree above 86 is as bad as one day with 10 degrees above it,” said Wolfram Schlenker.

Crops in Texas were found to be just as vulnerable as crops in colder regions like Minnesota when there are temperature extremes. The authors claim the best adaptation strategy is to develop more heat-resistant crops.

We also posted today on the availability of a new interactive tool, ClimateWizard, developed by The Nature Conservancy and researchers at two US universities, that allows anyone to see how temperature and precipitation patterns are changing over time, from 50 years ago, up to the year 2100.  The analysis supporting this tool also found that the US Heartland will experience greater heat gains than other regions of the country.

And in our series on impacts across regions in the US, drawn from the material in the June 2009 USGCRP report, Global Climate Change Impacts in the United States, we describe what the latest scientific literature reveals about what to expect in the Great Plains

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