But India, already one of the world's top polluters, has never measured methane emissions from its 4,500 large dams and has therefore never taken it into account in official data.

According to a study by scientists from Brazil's National Institute for Space Research, methane equivalent of 825 million tonnes of carbon dioxide is released annually by India's dams.

"I am quite positive that surface methane emission estimations are correctly estimated," said Ivan B.T. Lima, lead author of "Methane Emissions from Large Dams as Renewable Energy Resources: A Developing Nation Perspective".

"I am confident that Indian dams might be altering atmospheric methane although not precisely to what extent," Lima told Reuters in an e-mail interview.

India's carbon emissions, which excluded the contribution of methane from dams, were around 1,890 million tonnes in 2000, according to the World Resources Institute, a Washington-based environmental think-tank.

FLAWED RESEARCH?

Government officials say methane emissions from dams is not an issue.

"In India, the practice is that all the vegetation is removed before the water flows into the reservoir," said Prodipto Ghosh, a former environment secretary.

"So given that these are our practices in dam construction, you would believe any such study to be deeply flawed."

India, whose economy has surged between 8 and 9 percent in recent years, currently contributes around four percent of global emissions as its consumption of fossil fuels gallops.

But as a developing nation, it is not required to cut emissions, said to be rising 2 to 3 percent annually, under the Kyoto Protocol despite mounting pressure from environmental groups and developed nations.

India, which has the largest number of dams in the world after the US and China, has constructed many to service its farm sector, which makes up around 22 percent of the country's GDP and employs 70 percent of the workforce.

The dams have also been used to help power industry and bring electricity to some of the country's 1.1 billion people, most of whom live in villages.

But the dam constructions have frequently sparked protests for displacing tens of thousands of poor people, ravaging prime forests housing rare flora and fauna as well as destroying river ecosystems.

Activists said India's dam emissions were a serious concern and urged the government to conduct its own investigation.