Livermore, California
March 16, 2007
Warming temperatures since 1981
have caused annual losses of roughly $5 billion for the major
cereal crops, a study has found.
From 1981-2002, fields of wheat, corn and barley throughout the
world have produced a combined 40 million metric tons less per
year because of increasing temperatures caused by human
activities.
“There is clearly a negative response of global yields to
increased temperatures,” said David Lobell, a
Lawrence Livermore National
Laboratory researcher and lead author of the study that
appears online March 16 in Environmental Research Letters.
“Though the impacts are relatively small compared to the
technological yield gains over the same period, the results
demonstrate that negative impacts of climate trends on crop
yields at the global scale are already occurring.”
This is the first study to estimate how much global food
production already has been affected by climate change. Annual
global temperatures increased by about 0.7 degrees Fahrenheit
between 1980 and 2002, with even larger changes observed in
several regions.
“Most people tend to think of climate change as something that
will impact the future, but this study shows that warming over
the past two decades already has had real effects on global food
supply,” said Christopher Field, co-author on the study and
director of Carnegie Institution’s Department of Global Ecology.
Lobell and Field studied climate effects on the six most widely
grown crops in the world – wheat, rice, maize (corn), soybeans,
barley and sorghum (a genus of about 30 species of grasses
raised for grain). Production of these crops accounts for more
than 40 percent of global cropland area, 55 percent of non-meat
calories and more than 70 percent of animal feed.
Using global yield figures for 1961-2002 from the Food and
Agriculture Organization, Lobell and Field compared yields with
average temperatures and precipitation over the major growing
regions.
They found that, on average, global crop yields respond
negatively to warmer temperatures for several of the crops.
Lobell and Field then used these relationships to estimate the
effect of observed warming trends.
“To do this, we assumed that farmers have not yet adapted to
climate change, for example by selecting new crop varieties to
deal with climate change,” Lobell said. “If they have been
adapting – something that is very difficult to measure – then
the effects of warming may have been lower.”
Most experts believe that adaptation would lag several years
behind climate trends, because of the difficultly of
distinguishing climate trends from natural variability.
The importance of this study, the authors said, was that it
demonstrates a clear and simple relationship at the global
scale, with yields dropping by approximately 3-5 percent for a
one-degree Fahrenheit increase. “A key moving forward is how
well cropping systems can adapt to a warmer world,” Lobell said.
“Investments in this area could potentially save billions of
dollars and millions of lives.”
Founded in 1952, Lawrence Livermore National Laboratory has a
mission to ensure national security and apply science and
technology to the important issues of our time. Lawrence
Livermore National Laboratory is managed by the University of
California for the U.S. Department of Energy's National Nuclear
Security Administration. |
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