Large-scale changes in the world's climate probably will deepen the gap between the richest and poorest nations--potentially crippling food production in parts of Africa, South Asia and South America--according to the first worldwide assessment of food production and climate change.
Forty of the world's poorest countries are likely to see major losses in their ability to produce food--declines of up to 25%--if the climate continues to warm substantially, according to the assessment, which was released Tuesday at a major gathering of world climate scientists here.
The report emphasizes how differently global warming would affect various parts of the world. Nations in tropical climates, including India, Brazil and much of sub-Saharan Africa, would probably see huge losses in food production, it says.
More temperate climates, by contrast, could experience large gains in crop yields as higher temperatures lengthen growing seasons. Because nations in the tropics already are far poorer than those in the world's north, the impact on them could be catastrophic, with widespread starvation and malnutrition, the report projects. The projections cover several decades, with the full impact hitting by 2080.
For the poorest nations, "there is no margin for loss," said Mahendra Shah, one of the report's authors and a United Nations advisor and expert on land use from Austria's International Institute for Applied Systems Analysis.
"Many of these countries already have a food gap," he said, noting that the 40 countries considered most at risk now cope with 450 million malnourished people.
Globally, the report projects a small net increase in food production, but the effects on different areas would be uneven. Though poor nations would bear the heaviest burden as a group, some of the largest developing nations--China, Indonesia, Mexico, Chile, Congo and Kenya, for example--would probably see increased production.
Some developed countries, including Britain, the Netherlands and Australia, could see crop yields decline as warmer, wetter weather increases diseases and pests.
The overall impact on the United States--the world's largest emitter of so-called greenhouse gases, which are believed to contribute to global warming--is likely to be minimal, with possible small declines in the ability to grow cereal grains, according to the report.
The report is unique because, although others have tried to estimate the effect of climate change on individual countries, Shah and his colleagues attempted to analyze food production worldwide. Their work takes into account current climates, soil, terrain and land use.
The report comes as several developed countries, especially the U.S., are balking at ratifying the Kyoto Protocol, which seeks to limit emissions of greenhouse gases. One of the major arguments advanced by the Bush administration and other critics of the treaty is that it does not require developing countries to curb emissions.
The report's authors, however, assert that the developed countries, which emit the bulk of greenhouse gases, must ratify the treaty to prevent more suffering in poorer nations.
"The plight of the poorest countries must be at the center of negotiations," Shah said. "They have no voice."
"The report raises issues of equity and fairness," said one of the co-authors, Guenther Fischer. "The burden will undoubtedly fall disproportionately on the poorest and most vulnerable."
Though many scientists here applauded the study and called it the most thorough to date, it is not without its critics. Representatives of industries that have opposed the Kyoto agreement said any attempts to predict the effects of climate change on specific regions are notoriously unreliable.
Climate "modeling capability is so poor, it makes it impossible to do regional impacts. That right there calls the accuracy of the results into question," said Glenn Kelly, executive director of the Global Climate Coalition, a Washington-based group that represents business and industry.
Shah and his colleagues attempted to compensate for those uncertainties by using three international models of climate change to predict how food production would shift in this century.
Predictions differed slightly with each model, but under each, "developing countries lose as a group," Shah said. "Developed countries gain."
In nations close to the equator, crop losses would come as plants are stressed by heat and weakened by disease. Other declines could come as some regions dry out as a result of decreased rainfall and increased evaporation.
Robert Watson, chairman of the U.N.'s Intergovernmental Panel of Climate Change, said factors ranging from increased population to changes in land use will exacerbate the effects of climate change in struggling nations.
"Climate change is not simply an environmental issue," he added. "It is a development issue."
Yvo de Boer, a Dutch environment minister who is among the European leaders seeking to resuscitate the dying Kyoto Protocol, argued that developing countries should not be expected to do as much as developed countries to reduce emissions because they don't have the financial or technological resources and have historically contributed a small amount of greenhouse gases to the atmosphere.
"Damage caused by climate change exacerbates the inequities that already exist," De Boer said. Developing countries "are the first hit and the least able to defend themselves."