This is Bob Doughty with the VOA Special English AgricultureReport.
Scientists have had theories that climate change could harmcrops. Now, a study offers what it calls direct evidence that risingtemperatures at night can shrink harvests of rice.
Scientists from China, the Philippines and the United States didthe study for the International Rice Research Institute. Theinstitute is based outside Manila. The report appeared in the UnitedStates in the Proceedings of the National Academy of Sciences.
The researchers used weather information gathered overtwenty-five years at the institute’s own farm. They also usedinformation on rice harvests at the research farm fromnineteen-ninety-two until last year.
The scientists say every increase of one degree Celsius in theaverage daily temperature would decrease rice harvests by fifteenpercent. Earlier studies found half that estimate. That was becausethey did not consider the effects of temperatures at different timesof the day.
The new study found that theaverage daily temperature in the twenty-five year period increasedby seven-tenths of one degree. But nighttime temperatures increasedmore than a full degree. In fact, the increase was three timesgreater than the increase in daytimes temperatures. The scientistsfound that the daytime increase had no clear effect on productivity.
Professor Kenneth Cassman of the University of Nebraska-Lincolntook part in the study. He says the new findings could be explainedby the theories of scientists about the effects of global warming.
The scientists say industrial gasses trap heat in the atmosphere,so the ground cannot cool as much at night. Climate studies suggestthat average temperatures could increase as much as four-point-fivedegrees in the next one hundred years.
The researchers in the new study say higher nighttimetemperatures may cause the rice plants to spend less energy ongrowing. Other studies have suggested that grains like wheat andmaze act the same way. But scientists say more work must be done tounderstand how plants act under conditions of climate change.
Improved crops developed in the nineteen-sixties and seventiesmean that rice harvests are now two times greater. Rice productionhas kept up with population growth so far. But Professor Cassmansays the gains needed in the future could be more difficult.
This VOA Special English Agriculture Report was written by MarioRitter. This is Bob Doughty.