2004-7-5
This is Bob Doughty with the VOA Special English Agriculture
Report.
Scientists have had theories that climate change could harm
crops. Now, a study offers what it calls direct evidence that rising
temperatures at night can shrink harvests of rice.
Scientists from China, the Philippines and the United States did
the study for the International Rice Research Institute. The
institute is based outside Manila. The report appeared in the United
States in the Proceedings of the National Academy of Sciences.
The researchers used weather information gathered over
twenty-five years at the institute's own farm. They also used
information on rice harvests at the research farm from
nineteen-ninety-two until last year.
The scientists say every increase of one degree Celsius in the
average daily temperature would decrease rice harvests by fifteen
percent. Earlier studies found half that estimate. That was because
they did not consider the effects of temperatures at different times
of the day.
The new study found that the
average daily temperature in the twenty-five year period increased
by seven-tenths of one degree. But nighttime temperatures increased
more than a full degree. In fact, the increase was three times
greater than the increase in daytimes temperatures. The scientists
found that the daytime increase had no clear effect on productivity.
Professor Kenneth Cassman of the University of Nebraska-Lincoln
took part in the study. He says the new findings could be explained
by 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 suggest
that average temperatures could increase as much as four-point-five
degrees in the next one hundred years.
The researchers in the new study say higher nighttime
temperatures may cause the rice plants to spend less energy on
growing. Other studies have suggested that grains like wheat and
maze act the same way. But scientists say more work must be done to
understand how plants act under conditions of climate change.
Improved crops developed in the nineteen-sixties and seventies
mean that rice harvests are now two times greater. Rice production
has kept up with population growth so far. But Professor Cassman
says the gains needed in the future could be more difficult.
This VOA Special English Agriculture Report was written by Mario
Ritter. This is Bob Doughty.