Tropical crop yields may plummet, scientists warn

Posted: 3 December 2001

Harvests of some of the world'smost important food crops could fall by as much as a third in some crucial parts of the planet as a result of climate change, scientists are warning.

The decline would come at a time when there is an urgent need to raise yields to feed a growing, global, population.

The scientists have found evidence that rising temperatures, linked with emissions of greenhouse gases, can damage the ability of vital crops such as rice, maize and wheat, to flower and set seed. The studies indicate that for every one degree C rise in areas such as the Tropics, yields could tumble by as much as 10 per cent.

The Intergovernmental Panel on Climate Change (IPCC), the team of scientists that advise governments, estimates that average, global, temperatures in the Tropics could climb by as much as three degrees C by 2100.

Survival under threat

The findings on cash crops have come from GRID Arendal, a UN Environment Programme (UNEP)collaborative centre, based in southern Norway, with high-level skills in mapping.

Commenting on the research, Klaus Toepfer, Executive Director of UNEP, said: "Billions of people across the tropics depend on crops such as rice, maize and wheat, for their very survival. These new findings indicate that large numbers are facing acute hunger and malnutrition unless the world acts to reduce emissions of carbondioxide and other greenhouse gases".

Speaking in November 2001, at the climate change negotiations in Marrakech, Morocco, he added: "A similar threat to cash crops is also emerging in areas such as East Africa. Poor farmers here face declining yields and incomes in the traditional coffee and tea growing areas pushing them into even more biting poverty. Just to survive, they will be forced to clear forests in higher, cooler, areas. This can only add to environmental damage which in turn can lead to increased poverty, hunger and ill-health".

"I would urge governments...to remember the billions of people living at or near the poverty line whose lives face ruin as a result of global warming." Climate change treaties should not only be agreed and be effective, but brought into force as matter of urgency, he said.

Near thermal limits

The work by IRRI is being spearheaded by Dr John Sheehy, a crop ecologist. He said that many food crops grown in the tropics are at or near their thermal limits making it difficult for them to withstand further rises in temperature.

The Tropics are between the Tropic of Cancer and the Tropic of Capricon and include large swathes of Africa, Asia and Latin America.

"In rice, wheat and maize, grain yields are likely to decline by 10 per cent for every one degree C increase. This effect appears to occur when temperatures in the tropics climb over 30 degrees C during flowering. I would say we are at or close to this threshold where damage appears tooccur.

"Heat damage has been seen in Cambodia and India. We are certainly seeing significant temperature rises with average night time temperatures at our own centre in the Philippines now 2.5 degrees higher than they were 50 years ago," said Dr Sheehy.

Flowering is critical

He said preliminary studies indicated that other functions of the plant could also be damaged by high temperatures. But flowering is criticalbecause it is a one-off event from which there is no possibility of recovery from failure. "One possible research solution is to find geneswhich will make flowering occur during the cool of the early morning," said Dr Sheey.

The scientists are poised to launch the Global Challenge Programme to more precisely chart the likely effects of climate change on a wide range of crops.

"Initial results indicate that yields in the Tropics might fall as much as 30 per cent over the next 50 years, " said Dr Sheehy.

He said their forecasts did not include other potentially damaging developments as a result of global warming including a rise in agriculturalpests, impacts on pollinating insects and declines in rain fall.

Population growing fast

Under scenarios developed by the Intergovernmental Panel on Climate Change,global warming could benefit agricultural production in some areas of the globe such as Canada and Siberia.

But Dr Sheehy said these gains are unlikely to offset the losses in the tropics even if food surpluses in one region could be effectivelydistributed to those suffering shortages.

"The population of Asia is expected to increase by 44 per cent in the next 50 years and yields must at least match that growth rate if famine is to be avoided. Currently more than half the people in South East Asia have a calorie intake inadequate for an active life, and ten million children die annually from diseases related to malnutrition. So any decline in yields asa result of climate change will have alarming consequences," added the scientist whose team are urgently trying to develop new strains of key crops that are more heat tolerant.

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