To fairly divide the climate change fight between rich and poor, a new study suggests basing targets for emission cuts on the number of wealthy people, who are also the biggest greenhouse gas emitters, in a country.

Since about half the planet's climate-warming emissions come from less than a billion of its people, it makes sense to follow these rich folks when setting national targets to cut carbon dioxide emissions, the authors wrote on Monday in Proceedings of the National Academy of Sciences.

As it stands now, under the carbon-capping Kyoto Protocol, rich countries shoulder most of the burden for cutting the emissions that spur global warming, while developing countries -- including fast-growing economies China and India -- are not required to curb greenhouse pollution.

Rich countries, notably the United States, have said this gives developing countries an unfair economic advantage; China, India and other developing countries argue that developed countries have historically spewed more climate-warming gases, and developing countries need time to catch up.

The study suggests setting a uniform international cap on how much carbon dioxide each person could emit in order to limit global emissions; since rich people emit more, they are the ones likely to reach or exceed this cap, whether they live in a rich country or a poor one.

For example, if world leaders agree to keep carbon emissions in 2030 at the same level they are now, no one person's emissions could exceed 11 tons of carbon each year. That means there would be about a billion high emitters in 2030 out of a projected world population of 8.1 billion.

EACH PERSON'S EMISSIONS

By counting the emissions of all the individuals likely to exceed this level, world leaders could provide target emissions cuts for each country. Currently, the world average for individual annual carbon emissions is about 5 tons; each European produces 10 tons and each American produces 20 tons.

With international climate talks set to start this week in Italy among the countries that pollute the most, the authors hope policymakers will look at the strong link between how rich people are and how much carbon dioxide they emit.

You're distributing the task of doing something about emissions reduction based on the proportion of the population in the country that's actually doing the most damage, said Shoibal Chakravarty of the Princeton Environment Institute, one of the study's authors.

Rich people's lives tend to give off more greenhouse gases because they drive more fossil-fueled vehicles, travel frequently by air and live in big houses that take more fuel to heat and cool.

By focusing on rich people everywhere, rather than rich countries and poor ones, the system of setting carbon-cutting targets based on the number of wealthy individuals in various countries would ease developing countries into any new climate change framework, Chakravarty said by telephone.

As countries develop -- India, China, Brazil and others -- over time, they'll have more and more of these (wealthy) individuals and they'll have a higher share of carbon reductions to do in the future, he said.

These obligations, based on the increasing number of rich people in various countries, would kick in as each developing country hit a certain overall level of carbon emissions. This level would be set fairly high, so that economic development would not be hampered in the poorest countries, no matter how many rich people live there.

Is this a limousine-and-yacht tax on the rich? Not necessarily, Chakravarty said, but he did not rule it out: We are not by any means proposing that. If some country finds a way of doing that, it's great.

This week's climate talks in Italy are a prelude to an international forum in December in Copenhagen aimed at crafting an agreement to follow the Kyoto Protocol, which expires in 2012. At the same time, the U.S. Congress is working on legislation to curb U.S. carbon emissions.

Climate