* World's richest emit about half of Earth's carbon
* Tracking the wealthy could break climate impasse
* New method would follow individual greenhouse emissions
By Deborah Zabarenko, Environment Correspondent
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.