From The New York Times

THE CLIMATE DIVIDE; Wealth and Poverty, Drought and Flood: Reports From 4 Fronts In the War on Warming

By Andrew C. Revkin

April 3, 2007

Over the last few decades, as scientists have intensified their study of the human effects on climate and of the effects of climate change on humans, a common theme has emerged: in both respects, the world is a very unequal place.

In almost every instance, the people most at risk from climate change live in countries that have contributed the least to the atmospheric buildup of carbon dioxide and other greenhouse gases linked to the recent warming of the planet.

Those most vulnerable countries also tend to be the poorest. And the countries that face the least harm -- and that are best equipped to deal with the harm they do face -- tend to be the richest.

To advocates of unified action to curb greenhouse gases, this growing realization is not welcome news.

''The original idea was that we were all in this together, and that was an easier idea to sell,'' said Robert O. Mendelsohn, an economist at Yale. ''But the research is not supporting that. We're not in it together.''

The large, industrialized countries are more resilient partly because of geography; they are mostly in midlatitude regions with Goldilocks climates -- neither too hot nor too cold.

Many enjoy gifts like the thick, rich soil and generous growing season of the American corn belt or the forgiving weather of France and New Zealand.

But a bigger factor is their wealth -- wealth built at least partly on a century or more of burning coal, oil and the other fossil fuels that underlie their mobile, industrial, climate-controlled way of life.

The United States, where agriculture represents just 4 percent of the economy, can endure a climatic setback far more easily than a country like Malawi, where 90 percent of the population lives in rural areas and about 40 percent of the economy is driven by rain-fed agriculture.

As big developing countries like China and India climb out of poverty, they emit their own volumes of greenhouse gases; China is about to surpass the United States in annual emissions of carbon dioxide.

But they remain a small fraction of the total human contribution to the atmosphere's natural heat-holding greenhouse effect, which is cumulative because of the long-lived nature of carbon dioxide and some other heat-trapping gases. China may be a powerhouse now, but it has contributed less than 8 percent of the total emissions of carbon dioxide from energy use since 1850, while the United States is responsible for 29 percent and Western Europe 27 percent.

Disparities like these have prompted a growing array of officials in developing countries and experts on climate, environmental law and diplomacy to insist that the first world owes the third world a climate debt.

The obligation of the established greenhouse-gas emitters to help those most imperiled by warming derives from the longstanding legal concept that ''the polluter pays,'' many experts say.

''We have an obligation to help countries prepare for the climate changes that we are largely responsible for,'' said Peter H. Gleick, the founder of the Pacific Institute for Studies in Development, Environment and Security in Berkeley, Calif. His institute has been tracking trends like the burst of new desalination plants in wealthy places running short of water.

''If you drive your car into your neighbor's living room, don't you owe your neighbor something?'' Dr. Gleick said. ''On this planet, we're driving the climate car into our neighbors' living room, and they don't have insurance and we do.''

Around the world, there are abundant examples of how wealth is already enabling some countries to gird against climatic and coastal risks, while poverty, geography and history place some of the world's most crowded, vulnerable regions directly in harm's way.