World's
Most Important Crops Hit
By Global Warming Effects
By Steve Connor
23 March, 2007
The
Independent
Global warming over the past
quarter century has led to a fall in the yield of some of the most important
food crops in the world, according to one of the first scientific studies
of how climate change has affected cereal crops.
Rising temperatures between
1981 and 2002 caused aloss in production of wheat, corn and barley that
amounted in effect to some 40 million tons a year - equivalent to annual
losses of some £2.6bn.
Although these numbers are
not large compared to the world-wide production of cereal crops, scientists
warned that the findings demonstrated how climate change was already
having an impact on the global production of staple foods. "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
has already had real effects on global food supply," said Christopher
Field of the Carnegie Institution in Stanford, California.
The study, published in the
journal Environmental Research Letters, analysed yields of cereals from
around the world during a period when average temperatures rose by about
0.7C between 1980 and 2002 - although the rise was even higher in certain
crop-growing regions of the world.
There was a clear trend,
showing the cereal crops were suffering from lower yields during a time
when agricultural technology, including the use of chemical fertilisers
and pesticides, became more intensive. The study's co-author, David
Lobell of America's Lawrence Livermore National Laboratory in California,
said that the observed fall in cereal yields could be clearly linked
with increased temperatures during the period covered by the study.
"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,"
Dr Lobell said.
The two scientists analysed
six of the most widely grown crops in the world - wheat, rice, maize,
soybeans, barley and sorghum. Production of these crops accounts for
more than 40 per cent of the land in the world used for crops, 55 per
cent of the non-meat calories in food and more than 70 per cent of animal
feed.
They also analysed rainfall
and average temperatures for the major growing regions and compared
them against the crop yield figures of the Food and Agriculture Organisation
for the period 1961 to 2002.
"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," Dr Lobell
said.
"If they have been adapting,
something that is very difficult to measure, then the effects of warming
may have been lower," he said.
The study revealed a simple
relationship between temperature and crop yields, with a fall of between
3 and 5 per cent for every 0.5C increase in average temperatures, the
scientists said.
© 2007 Independent News
and Media Limited.
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