Scientists warn that agricultural harvests in some parts of the world could fall by about one-third as global temperatures increase. Farmers growing crops like rice and wheat will find it harder to set seed, and they will have to find new places to grow crops like tea and coffee.

Dr. John Sheehy, a crop ecologist at the International Rice Research Institute, says many food crops grown in the tropics are at or near their thermal limits, and will find it difficult to cope with further temperature rises. ?In rice, wheat and [corn], grain yields are likely to decline by 10% for every one degree Celsius [33.8 degrees F] increase in temperature. This effect appears to occur when temperatures in the tropics climb over [86 degrees Fahrenheit] during flowering. I would say we are at or close to this threshold,? Sheehy says. ?Heat damage has been seen in Cambodia and India. Initial results indicate that yields in the tropics might fall as much as 30% over the next 50 years.?

The Intergovernmental Panel on Climate Change estimates that the global temperature rise from 1990 to 2100 will turn out to be somewhere between [34.5] and [42.4 degrees Fahrenheit]. The most likely increase, with a 50% probability, will be between [36.3] and [38.8 degrees Fahrenheit]. Night temperature changes might damage plants? ability to produce pollen, and even a small decline in yields could prove devastating.

?The population of Asia is expected to increase by 44% in the next 50 years, and yields must at least match that growth rate if famine is to be avoided,? says Sheehy. ?Currently more than half the people in southeast Asia have a calorie intake inadequate for an active life, and 10 million children die annually from diseases related to malnutrition.?

UN Environment Program scientists are concerned that higher temperatures will make it harder for African farmers to produce tea and coffee because traditional areas in Uganda and Kenya will have become too warm, forcing farmers to clear cooler land higher up. There will be similar problems for Asia, Latin America and the Caribbean.

The director, Dr. Klaus Toepfer, says, ?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.?

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