China's lesser-developed heartland is responsible for 80 percent of carbon dioxide emissions related to goods consumed along the wealthier coast, international researchers said Monday.

China is the world's largest emitter of carbon dioxide, and has vowed to reduce such emissions per unit of gross domestic product by 40 to 45 percent of the country's 2005 levels by 2020.

But the study in the US journal the Proceedings of the National Academy of Sciences suggests that current efforts to cut harmful greenhouse gases fall short because of the way they set targets for the highest polluting areas.

"China has set emissions targets which are more stringent in affluent coastal provinces than in less-developed interior provinces," said study co-author Laixiang Sun, a researcher at the University of Maryland.

"This may reduce emissions in one region, but in China as a whole, you find CO2 emissions continue to increase, because the polluting factories move into the less-developed regions."

China pumped out some 10 gigatons of carbon dioxide in 2011.

The current study is based on data available in 2007 when that figure was 7.2 gigatons, and used an economic input-output model to track trade flows across sectors and regions.

A total of 57 percent of China's fossil fuel emissions came from producing items that were eventually consumed in a different province or in another country, researchers found.

Up to 80 percent of emissions related to goods consumed in places like Beijing, Tianjin, Shanghai, and Guangdong were due to imports from less-developed central and western provinces, it said.

When accounting for the pollution linked to exports from the affluent coastal regions, researchers found that 40 percent of those emissions originated in central, northern, and western China.

In those lesser populated, interior regions of the country, inefficient technologies and factories that pump out fossil fuel pollution are widespread.

However, as part of China's pledge to cut pollution in increments, its plan to reduce carbon levels by 2015 calls for just a 10 percent cut in the west and 19 percent along the east coast.

"This is regrettable, because the cheapest and easiest reductions -- the low-hanging fruit -- are in the interior provinces, where modest technological improvements could make a huge difference in emissions," said University of California, Irvine climate change researcher Steve Davis.

"Richer areas currently have much tougher targets, so it's easier for them to just buy goods made elsewhere. A nationwide target that tracks emissions embodied in trade would go a long way toward solving the problem. But that's not what's happening."

The study also included researchers from the University of London, Austria's International Institute for Applied Systems Analysis, the University of Leeds, the Chinese Academy of Sciences, the University of Cambridge and the University of Chinese Academy of Sciences.