You may remember seeing scare stories like these in the media.
Claim: Climate Change will Cause a Global Corn Crop Failure
Reality bites in two ways; 1. Actual data shows yield increases, and 2. New study says warming has actually helped corn yields.
Research links warming temperatures and localized cooling to increased maize production
The past 70 years have been good for corn production in the midwestern United States, with yields increasing fivefold since the 1940s. Much of this improvement has been credited to advances in farming technology but researchers at Harvard University are asking if changes in climate and local temperature may be playing a bigger role than previously thought.
In a new paper, researchers found that a prolonged growing season due to increased temperatures, combined with the natural cooling effects of large fields of plants, have had a major contribution to improved corn production in the U.S.
“Our research shows that improvements in crop yield depend, in part, on improvements in climate,” said Peter Huybers, Professor of Earth and Planetary Sciences in the Department of Earth and Planetary Sciences (EPS) and of Environmental Science and Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS).
“In this case, changing temperatures have had a beneficial impact on agricultural production, but there is no guarantee that benefit will last as the climate continues to change. Understanding the detailed relationships between climate and crop yield is important as we move towards feeding a growing population on a changing planet.”
The research is published in the Proceedings of the National Academy of Sciences (PNAS).
“Understanding the detailed relationships between climate and crop yield is important as we move towards feeding a growing population on a changing planet.”
The researchers modeled the relationship between temperature and crop yield from 1981 to 2017 across the so-called Corn Belt: Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Nebraska, Ohio, South Dakota, and Wisconsin. They found that as temperatures increased due to global climate change, planting days got earlier and earlier, shifting by about three days per decade.
“One of farmers’ biggest decisions is what they plant and when they plant it,” said Ethan Butler, first author of the paper and former graduate student in EPS. “We are seeing that farmers are planting earlier – not only because they have hardier seeds and better planting equipment — but also because it’s getting warmer sooner.”
Butler is currently a Postdoctoral Research Associate in the Department of Forest Resources at the University of Minnesota.
Early planting means the corn has more time mature before the end of the growing season.
There is also a second, more surprising trend that has benefited corn yields. Whereas the vast majority of temperatures have warmed over the last century, the hottest days during the Midwestern growing season have actually cooled.
“Increasingly productive and densely-planted crops can evaporate more water from leaves and soils during hot days,” said Nathaniel Mueller, a former postdoctoral research fellow at the Harvard University Center for the Environment and co-author of the paper. “Widespread increases in rates of evaporation apparently helps shield maize from extreme heat, cooling the surrounding area and helping to boost yields.”
Mueller is currently an Assistant Professor of Earth System Science at the University of California, Irvine.
The researchers estimate that more than one-quarter of the increase in crop yield since 1981 can be attributed to the twin effects of a longer growing season and less exposure to high temperatures, suggesting that crop yield is more vulnerable to climate change than previously thought.
The researchers also show that the planting and harvest dates farmers currently use is significantly better adapted to the present climate than it would be to climates in earlier decades.
“Farmers are incredibly proactive and we’re seeing them take advantage of changes in temperature to improve their yield. The question is, how well can they continue to adapt in response to future changes in climate,” said Huybers.
This research was supported in part by the Packard Foundation and the National Science Foundation.
The paper (open access) http://www.pnas.org/content/early/2018/10/31/1808035115
Peculiarly pleasant weather for US maize
Over the course of the 20th century, US maize yields have improved by more than a factor of five. Whereas this trend is often attributed exclusively to technological improvements, here, we also identify contributions from improved temperatures during the growing season. More than one-quarter of the increase in crop yield since 1981 is estimated to result from trends toward overall warmer conditions, but with cooling of the hottest growing-season temperatures, and from adjustments in crop timing toward earlier planting and longer maturation varieties.
Continuation of historical trends in crop yield are critical to meeting the demands of a growing and more affluent world population. Climate change may compromise our ability to meet these demands, but estimates vary widely, highlighting the importance of understanding historical interactions between yield and climate trends. The relationship between temperature and yield is nuanced, involving differential yield outcomes to warm (C) and hot (C) temperatures and differing sensitivity across growth phases. Here, we use a crop model that resolves temperature responses according to magnitude and growth phase to show that US maize has benefited from weather shifts since 1981. Improvements are related to lengthening of the growing season and cooling of the hottest temperatures. Furthermore, current farmer cropping schedules are more beneficial in the climate of the last decade than they would have been in earlier decades, indicating statistically significant adaptation to a changing climate of 13 kg·ha−1· decade−1. All together, the better weather experienced by US maize accounts for 28% of the yield trends since 1981. Sustaining positive trends in yield depends on whether improvements in agricultural climate continue and the degree to which farmers adapt to future climates.