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Too hot for the iron rice bowl

The US National Academy of Sciences journal is not normally a must-read publication for policymakers in Asia. But they would be wise to take note of findings that show how rice growth and grain yield will be more seriously affected by global warming than previously predicted. The conclusion is important because 90 per cent of all rice is grown and eaten in China and other parts of Asia. It is the staple food for 2 billion people. Shortages or high prices of basic food have in the past led to riots and political instability.

Industrial and transport growth around the world pump out ever more carbon dioxide and other so-called 'greenhouse' gases that warm the atmosphere. Agriculture, too, contributes to this warming effect because some animals and plants, including rice, emit large quantities of methane.

Temperatures are projected to rise by between 1.5 and 4.5 degrees Celsius in the coming century. The latest climate research concludes that rice yields will fall 15 per cent for every one degree Celsius rise in the mean daily temperature. This is twice the previous estimate. Global warming thus threatens to erase hard-won productivity gains.

This prediction is especially significant for China. With a population of 1.3 billion, it has always put grain security high on its policy agenda. Yet grain output - chiefly rice, wheat and corn - has declined for the past five years, to 431 million tonnes last year, below the government's minimum output target of 450 million tonnes.

China has just 123 million hectares of farmland, or about 0.095 hectares per person - less than half the world average. According to official figures, nearly 7 million hectares of arable land have been lost to industrial development and urban expansion in the past seven years. Measures have been taken to try to slow this loss and boost grain production. But rapid economic growth is leading to more jobs in cities, and labour shortages on farms. Officials estimate that the annual rice harvest will reach a 12-year low of 85 million tonnes by the end of this year, down 27 per cent on last year, and the worst result in more than 10 years. Prices in some areas have risen by 70 per cent since October.

Global warming can only make the situation more precarious. The field studies carried out at the International Rice Research Institute in the Philippines and published in the National Academy of Sciences journal confirmed predictions that global warming will make rice crops less productive. However, by combining 25 years of climate data collected at the institute with yield trends in adjacent fields over the past 12 years, researchers discovered that simulation models underestimated the problem by half because they overlooked the retarding effect of high minimum night temperatures. Since 1979, climate data gathered by the institute shows that the rise in air temperature was three times greater at night than during the day.

'Most studies of temperature and global warming effects on crop growth and grain yield are based on daily mean air temperature, which assumes no difference in the influence of the day versus night temperature,' wrote the nine-member research team from the institute, China and the United States, led by crop physiologist Peng Shaobing. 'This report provides direct evidence of decreased rice yields from increased temperature associated with global warming.' Dr Peng says that the challenge is to find the financial resources to develop new varieties that can still produce good yields even with temperature rises.

If science fails, however, Asia may have to choose between strengthening its agricultural roots and slowing breakneck economic growth.

Michael Richardson, a former Asia editor of the International Herald Tribune, is a visiting senior research fellow at the Institute of South East Asian Studies in Singapore. The views expressed in this article are those of the author