63-82% Cut in US Crop Yields for Temperature Alone …

We are at or above A1F1. This confirms major crop losses to North America when the summer Arctic sea ice goes.

Wolfram Schlenker and Michael J. Roberts

Nonlinear temperature effects indicate severe damages to U.S. crop

yields under climate change

PNAS 2009 106:15594-15598; published online before print August 28,

2009, doi:10.1073/pnas.0906865106

Nonlinear temperature effects indicate severe damages to U.S. crop

yields under climate change

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.

climate US agro.doc


~ by Cory Morningstar on November 21, 2009.

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