Global Warming May Boost Crop Yields, Study Says

John Pickrell
for National Geographic News
November 25, 2002

Escalating greenhouse gas levels may significantly boost production of fruits and seeds in crops such as wheat, rice, and soybeans, according to a recent study.

But the effect may be a double-edged sword; the increase in yield appears to be linked to a decrease in the nutritional value of these crops.

"Crops have higher yields when more [carbon dioxide] is available, even if growing conditions aren't perfect," said Peter S. Curtis, an ecologist at Ohio State University and co-author of the study. "But there's a trade-off between quantity and quality. While crops may be more productive, the resulting produce will be of lower nutritional value."

The findings could impact scientific thinking.

"There is no doubt but that quality matters," said Robert Mendelsohn, an environmental economist at Yale University. "If scientists can demonstrate a distinct loss of quality, this would be important and could change our impression of the global impact of climate change on agriculture from benign to harmful."

Gaseous Fertilizer

Carbon dioxide is a natural element in the Earth's atmosphere, and plants use it as a kind of "gaseous fertilizer," said Curtis.

However, human activities such as burning fossil fuels for heat, electricity, transportation, industry, and other purposes, are increasing the levels of carbon dioxide in the atmosphere.

Carbon dioxide, methane, nitrous oxide, and other gases are known collectively as greenhouse gases because they trap heat in the atmosphere. Most scientists believe the increasing levels of carbon dioxide and other greenhouse gases is causing global climate changes that could melt ice caps, raise sea levels, create deserts, and intensify adverse and unpredictable weather conditions such as tropical storms.

To understand the role that rising carbon dioxide levels might have on plant growth, Curtis and his colleagues pulled together data from 159 studies published over the last 20 years. These studies detailed the effects of higher-than-usual carbon dioxide levels on 79 plant species. The species included domesticated crops such as corn, cotton, wheat, and rice, as well as wild plants such as heath plants (blueberry and cranberry, for instance), wild radish, plantains, and pasture grasses.

Other researchers have summarized the positive effect of elevated carbon dioxide on leaves, stems and roots, said Curtis, but few have examined the overall effects on the reproductive traits of plants—seed and fruit number, size, and nutritional quality.

"Reproductive traits are key characteristics for predicting the response of communities and ecosystems to global change," said Curtis.

Continued on Next Page >>


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