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Global warming could hurt crop yields: study

India will be among the harder-hit regions; half of the world’s population could face serious food shortages

india Updated: May 21, 2010 10:31 IST

Bangalore: Global warming could seriously dent crop yields in the tropics and subtropics, including India by the end of the century, and if the agriculture systems don’t adapt, at least half of the world’s population could face serious food shortages, says a new report in Friday’s Science.

Using data from 23 climate models, which contributed to the Intergovernmental Panel on Climate Change, or IPCC, 2007 report, David S. Battisti, University of Washington, and Rosamond L. Naylor of Stanford University’s Program on Food Security and the Environment say India will be among the harder-hit regions due to its high growing-season heat and decrease in soil moisture.

Researchers say there is greater than a 90% probability that by 2100 the lowest growing-season temperatures in the tropics and subtropics will be higher than any temperatures recorded there to date. The temperate zones won’t be spared either, even though the IPCC is optimistic about them.

“It’s a very interesting approach at looking into the future and has a serious message for India. IPCC has not done such an analysis,” says N.H.

Ravindranath, professor at the Centre for Ecological Sciences, Indian Institute of Science in Bangalore and co-author in most of the IPCC climate reports.

Unlike other reports, this study has used historical instances of extreme warming, hurricane, drought, etc. to illustrate the magnitude of damage to food production, showing that these short-run extreme events could become the norm in later part of the century.

The study includes severe heat episodes in France in 2003, Ukraine in 1972 and Sahel, western Africa, in the 1960s-70s. In the case of the Ukraine, a near-record heat wave reduced wheat yields and contributed to disruptions in the global cereal market that lasted two years. “We are taking the worst of what we’ve seen historically and saying that in the future it is going to be a lot worse unless there is some kind of adaptation,” says Naylor. Though India has had many instances of high seasonal heat (and extreme heat waves), Battisti and Naylor say they couldn’t include those examples in their study as there is not enough documentation of damage from these events. Most documentation for India and other parts of Asia focuses on drought episodes as opposed to heat episodes.

That’s true, we don’t scientifically document such events and crop damages, says Ravindranath. India had severe drought and heat episodes as recent as in 2000 and 2001 in Gujarat, Rajasthan, Karnataka and other parts but the crop yield was not assessed, as they were considered extreme events. But this could be the norm in next 50 years, says Ravindranath. For instance, the IPCC predicts 2-3 degrees centigrade change in temperature in Europe by 2050. But Europe already experienced such a rise in temperature in 2003 when an estimated 52,000 people died and various crops faced decline in yield ranging from 35 to 21%.

This could serve as a good example for policy makers, says Ravindranath, who, as part of several New Delhi committees on climate policy, regrets India not basing its climate policy on “sound scientific and economic analysis”.

Scientists say this finding provides a compelling reason for investment in adaptation as it will take decades to develop new food crop varieties that have more heat tolerance. In the tropics, the higher temperatures can cut yields of the staple crops such as rice and maize by 20-40%. Even crops such as wheat, says Battisti, which makes up one-quarter of the calories consumed in India, have not seen any growth in yields for the last decade. He suggests “the government of India should take these projections seriously”, as the ensemble of models in this study includes all of the science that contributed to the

IPCC and is the “best available in the world”. “India has to worry about its own crop productivity; it also has to worry about migration from other regions of South Asia, notably Bangladesh, when sea level rises and wipes out a large share of their agricultural region,” says Naylor.