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Experts: Decline in Rice Yields Linked to Global Warming - 2004-07-07


In Hollywood's version of climate change, New York gets buried under an ice sheet. Science isn't usually that dramatic, but a new study indicates that food production could take a hit in a global warming scenario. The research links a decline in crop yields with warmer temperatures.

Shaobing Peng of the International Rice Research Institute and his colleagues analyzed 25 years worth of weather and production data at the institute's farm in the Philippines. Over that period, there was a average temperature increase of about three-quarters of a degree Celsius, but most of the increase was at night. In other words, it wasn't getting as cool after sundown.

According to Kenneth Cassman, an American researcher on the team, the higher nighttime temperatures force the rice plants to, in effect, work harder.

"And what happens then is that diverting energy to maintain important metabolic functions that keep the plant alive during the nighttime diverts energy away from producing biomass and grain yield," he explained.

The effect is quite dramatic. The researchers concluded that rice yield declined by 10 percent for each one-degree increase in minimum nighttime temperature.

"The elevated temperature, we believe, increases what we call the 'maintenance respiration costs' of the plant at night. That is, the amount of energy the plant needs to use to keep itself alive during the nighttime," said Mr. Cassman.

Professor Cassman says that the rice was under controlled conditions where best growing practices were in place.

"So that the yields aren't limited by weeds or insects or diseases or nutrient deficiencies or water - too much water, too little water - so that year in and year out, the only thing that determines the yield of that crop is the amount of solar radiation and the temperature," he said.

Previous studies, using computer simulations or hothouse experiments, also predicted declining yields with higher temperatures. But the University of Nebraska researcher says the real world data used in this study indicates the effect of higher temperatures is even greater than predicted by earlier experiments.

"Our study shows that the magnitude of the yield decrease due to increasing night temperatures that we measured from the field studies was double the rate of decrease predicted by computer simulation models," Mr. Cassman went on to say.

Rice, along with wheat and maize, is one of the top three food crops on planet Earth. And Professor Kenneth Cassman points out that feeding an increasing population when warmer climates could cut production presents a critical challenge for the world's farmers in the years ahead.

The study of rice yields was published in the Proceedings of the National Academy of Sciences.

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