IPCC co-chair Martin Parry said that rains that nourish crops are pushing toward the poles and away from the arid regions nearer the Equator that need them most.
"It's exactly what we don't want," he said. "It makes the world much less even and more inequitable. We've got 500 million hungry people in the world today. Those numbers are likely to increase as a result of climate change."
Yields of cereals and other crops are likely to increase in northern countries, Parry said, but there's a temperature tipping point at which overall food production starts to fall.
"At about one or two degrees you get a global downturn in productivity," he said.
Water Shortages, Lusher Northern Forests
The IPCC's other main forecasts include:
More than a billion people may face freshwater shortages by 2050, especially in Asia, where rising living standards will lead to increased water demand.
Millions more will be threatened by floods due to rising sea levels, with island inhabitants and populations in large river-delta regions in Asia most at risk.
Mountain ecosystems could lose more than half of their wildlife species by 2080 if greenhouse gas emissions continue unchecked, with winter tourism set to dwindle along with snow cover and glaciers.
Coral bleaching due to ocean warming will cause massive reef die-offs unless coral species can adapt. (Related: "Global Warming Has Devastating Effect on Coral Reefs, Study Shows" [May 16, 2006].)
Dry areas may become drier, with crop yields dropping by as much as 50 percent in sub-tropical regions by 2020. (Related: "U.S. Southwest Drought Could Be Start of New Dust Bowl" [April 5, 2007].)
Commercial timber production could rise globally with increased rates of tree growth in northern countries.
Higher rates of climate-related illness, including malnutrition, malaria, dengue fever, and heatstroke could take effect.
The report is the second of three being released this year as part of IPCC's latest global climate assessment—the fourth such assessment carried out since the panel was created in 1988.
The final report will focus on ways to combat climate change by reducing the amounts of carbon dioxide and other heat-trapping greenhouse gases being poured into the atmosphere by the burning of fossil fuels and other human activities.
Environmentalists said the latest IPCC findings highlight the need for urgent action by countries to cut greenhouse gas pollution.
"From turtles to tigers, from the [Mexican] desert of Chihuahua to the great Amazon—all these wonders of nature are at risk from warming temperatures," WWF climate change scientist Lara Hansen said in a statement.
"While adaptation to changing climate can save some, only drastic action by governments to reduce emissions can hope to stop their complete destruction," she added.
Cold-loving animals such as polar bears will find it difficult to keep pace with the rapid temperature change, causing local extinctions, said zoologist Love Dalén of Royal Holloway University of London.
"The arctic fox may disappear from continental Europe, Asia, and North America, surviving only on Arctic islands," he added.
Dalén noted, however, that these animals have faced and survived the challenge of climate warming in the past.
At the same time, aid organizations expressed fear that the effect of more severe drought in Third World countries will trigger human impacts including forced migration and armed conflict.
International Alert, an independent peace-building organization, has identified 61 countries that face the "double-headed risk" of climate change and conflict potential.
"If these conflicts turn violent, they will be fought out across divisions marked out by ethnicity, religion, and political allegiances," International Alert secretary general Dan Smith said.
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