Cereal Crops Feel the Heat

Cereal Crops Feel the Heat



March 2007 - Warming 
temperatures since 1981 have caused annual losses of about 
US$5 billion for six major cereal crops, new research has 
found. This is the first study to estimate how much global 
food production already has been affected by climate change. 
From 1981 to 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 today in "Environmental Research 
Letters" online. 
"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," said 
Lobell. 
Annual global temperatures increased by about 0.7 degrees 
Fahrenheit between 1980 and 2002, with even larger changes 
observed in several regions. 
Effects of early drought on a wheat crop in the UK. April 
2002. 
"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 in Stanford, California. 
Lobell and Field studied climate effects on the six most 
widely grown crops in the world – wheat, rice, soybeans, 
barley, maize or corn, 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 United 
Nations 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 difficulty of 
distinguishing climate trends from natural variability. 
The importance of this study, the authors say, is that it 
demonstrates a clear and simple relationship at the global 
scale, with yields dropping by approximately three to five 
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." 
Agriculture's vulnerability to global warming was revealed 
late last year when the Consultative Group on International 
Agricultural Research, CGIAR, a network of 15 of the world's 
top crop research centers, issued an estimate of the impact of 
climate change on a single cereal crop, wheat, in one of the 
world's breadbasket regions. 
Researchers using computer models to simulate the weather 
patterns likely to exist around 2050 found that the best wheat 
growing land in an arc from Pakistan through Northern India 
and Nepal to Bangladesh would be destroyed. Much of the area 
would become too hot and dry for growing wheat, placing 200 
million people at greater risk of hunger. 
Water stress in the rice paddy. The lack of water in the soil 
reduces the ability of the plant to extract essential 
nutrients from the soil. 
CGIAR also warned in December that famines lie ahead unless 
new crop strains adapted to a warmer future are developed. To 
avert famine, CGIAR announced plans in December to accelerate 
efforts aimed at developing new strains of staple cereal crops 
including maize, wheat, rice and sorghum. 
"The impacts of climate change on agriculture will add 
significantly to the development challenges of reducing 
poverty and ensuring sufficient food production for a growing 
population," said Dr. Robert Zeigler, director general of the 
International Rice Research Institute, a CGIAR supported 
research center. 
"The livelihoods of billions of people in developing 
countries, particularly those in the tropics, will be severely 
challenged as crop yields decline due to shorter growing 
seasons," Zeigler said. 
CGIAR researchers are focused on a comprehensive climate 
change agenda that is already generating climate-resilient 
innovations, including crops bred to withstand heat, salt, 
submergence or waterlogging, and drought, and more efficient 
farming techniques to help poor farmers better use 
increasingly scarce water and fragile soil. 
Researchers are also focusing on boosting agriculture’s role 
in reducing climate-altering greenhouse gases. 
"Anticipating and planning for climate change is imperative if 
farmers in poor countries are to avert forecast declines in 
yields of the world’s most important food crops,” said Dr. 
Louis Verchot, a climate change scientist with the CGIAR 
supported World Agroforestry Centre in Kenya. "Yet, adaptation 
is not a substitute for reducing new and removing existing 
greenhouse gases from the atmosphere - our only long-term 
option." 
As a result of rising temperatures, the climatic conditions 
best suited to wheat growing will shift away from the tropics, 
where most of the world’s poorest countries are situated, 
toward the poles and to higher elevations. 
CGIAR expects that North American wheat growers will be able 
to farm new lands as far as 65 degrees north, 10 degrees 
beyond their current planting limit. Wheat growing would 
extend from its current limit – from Ketchikan, Alaska in the 
West to Cape Harrison, Labrador in the East – to less than two 
degrees beneath the Arctic Circle. 
In Eurasia, much of Siberia would become farmland. 
While poor tropical countries' capacity for food production 
will diminish, developed countries, most of which are located 
far from the equator, will experience an increase in 
productive capacity as land that was previously frost-bound 
opens to cultivation. 
Said Dr. Verchot, "Developing countries, which are already 
home to most of the world's poor and malnourished people and 
have contributed relatively little to the causes of global 
warming, are going to bear the brunt of climate change and 
suffer most from its negative consequences." 





 

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