U.S. corn belt defies global warming trend

Although the global average temperature has increased 1.4 degrees Fahrenheit over the past 100 years, the corn belt of the U.S., one of the most agriculturally productive regions of the world, has experienced a decrease in temperatures in the summer during the growing season. Known as the “U.S. warming hole,” this anomalous cooling phenomenon, which occurred in tandem with increasing rainfall, was responsible for boosting corn yields by 5%–10% per year, according to a new study published in Environmental Research Letters.

Most of the increases in corn yield over the 20th century have resulted from advancements in crop genetics, increased fertilizer application, and improved agricultural practices. “If however, the U.S. warming hole had not existed, corn yields for the average county in the central U.S. would have been approximately 10% lower per year,” explained lead author Trevor F. Partridge, a graduate student in the department of earth sciences at Dartmouth. “This benefit of a 10% higher corn yield translates to roughly $1.5 billion per year in additional value. Our results underscore how the central U.S. has been relatively sheltered from the impacts of climate change,” he added.

To examine the relationship between corn yields and climate, the researchers used over 70 years of historical climate and yield data, machine learning algorithms, and biophysical crop models to simulate corn yields under multiple climate scenarios. The scenarios included historical climate with the warming hole, where temperatures dropped in the late-1950s and rainfall increased.

The researchers found that cooler temperatures associated with the warming hole were responsible for most of the increased U.S. corn yield—62% of the simulated yield increase, whereas, summer precipitation was responsible for the remaining 38% of the simulated yield increase. The lower temperatures allowed corn to mature slower. Extended maturation time allows for more grain to accumulate on a corn plant, increasing yields.

The authors emphasize that the U.S. warming hole is an anomaly, one of two places in the world that has not warmed significantly. Climate projections suggest that by the mid-21st century, temperatures in the central U.S. will increase by up to 4.1 degrees Fahrenheit, and summer precipitation may decrease by approximately 10%. “The boost in yield that the corn belt has enjoyed from the effects of the warming hole is likely to diminish in the future. While this region has been an anomaly for the past half century, we need to be prepared for the challenges associated with climate change,” said co-author Jonathan Winter, an assistant professor of geography at Dartmouth.

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