Crops Feel The Heat As The World Warms*

The researchers focused 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 grass raised for grain. These crops occupy more than 40
percent of the world's cropland, and account for at least 55 percent of
non-meat calories consumed by humans. They also contribute more than 70
percent of the world's animal feed. The main value of this study, the
authors said, was that it demonstrates a clear and simple correlation
between temperature increases and crop yields at the global scale.

by Staff Writers
Stanford CA (SPX) Mar 20, 2007

Over a span of two decades, warming temperatures have caused annual
losses of roughly $5 billion for major food crops, according to a new
study by researchers at the Carnegie Institution and Lawrence Livermore
National Laboratory.

 From 1981-2002, warming reduced the combined production of wheat, corn,
and barley-cereal grains that form the foundation of much of the world's
diet-by 40 million metric tons per year. The study, which will be
published March 16 in the online journal Environmental Research Letters,
demonstrates that this decline is due to human-caused increases in
global temperatures.

"Most people tend to think of climate change as something that will
impact the future," said Christopher Field, co-author on the study and
director of Carnegie's Department of Global Ecology in Stanford, Calif.
"But this study shows that warming over the past two decades has already
had real effects on global food supply."

The study is the first to estimate how much global food production has
already been affected by climate change. Field and David Lobell, lead
author of the study and a researcher at Lawrence Livermore National
Laboratory, compared yield figures from the Food and Agriculture
Organization with average temperatures and precipitation in the major
growing regions.

They found that, on average, global yields for several of the crops
responded negatively to warmer temperatures, with yields dropping by
about 3-5 percent for every 1 degree F increase. Average global
temperatures increased by about 0.7 degrees F during the study period,
with even larger changes in several regions.

"Though the impacts are relatively small compared to the technological
yield gains over the same period, the results demonstrate that negative
impacts are already occurring," said Lobell.

The researchers focused 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 grass raised for grain. These crops occupy more than 40
percent of the world's cropland, and account for at least 55 percent of
non-meat calories consumed by humans. They also contribute more than 70
percent of the world's animal feed.

The main value of this study, the authors said, was that it demonstrates
a clear and simple correlation between temperature increases and crop
yields at the global scale. However, Field and Lobell also used this
information to further investigate the relationship between observed
warming trends and agriculture.

"We assumed that farmers have not yet adapted to climate change-for
example, by selecting new crop varieties to deal with climate change. If
they have been adapting-something that is very difficult to measure-then
the effects of warming may have been lower," explained Lobell.

Most experts believe that adaptation would lag several years behind
climate trends, because it can be difficult to distinguish climate
trends from natural variability. "A key moving forward is how well
cropping systems can adapt to a warmer world. Investments in this area
could potentially save billions of dollars and millions of lives,"
Lobell added.