China's booming economy and record levels of coal production appear to be driving a rise in global methane emissions, according to new research.

A study published yesterday in the international science journal Nature warns methane emissions from human activities have been increasing over the past seven years.

However, their global warming impact was counteracted by a reduction in methane emissions from northern Asia's wetlands over the same period - ironically, because of drier conditions caused by climate change.

One of the study's authors, CSIRO atmospheric scientist Paul Steele, said, "One balanced the other out, so the net increase in methane emissions was zero, but it masked the fact that human-made sources of methane were continuing to rise."

Methane emissions from human sources stabilised inthe early 1990s largely as a result of more efficient use of natural gas in the northern hemisphere, but began to rise againin 1999, Dr Steele said.

Methane is the second-most important greenhouse gas after carbon dioxide, and is estimated to warm the earth at a rate 23 times greater than carbon dioxide over a period of 100 years. Recent CSIRO research has shown atmospheric levels have tripled over the past 200 years, rising by 150 percent.

Dr Steele said satellite images showed the area of wetlands across Asia had significantly decreased, reducing emissions from rotting vegetation.

A drop in the global growth rate of methane emissions from 1991-93, was partially caused by the economic collapse of the former Soviet Union, the Nature paper says. But during 1997-98, "large abnormal peat fires in Indonesia" released huge amounts of methane into the atmosphere from smouldering combustion.

Dr Steele said methane emissions from coal mining had also contributed to the rise in methane emissions.

Coal contains methane gas, which is released during mining and emitted into the atmosphere through mine exhaust ventilation know as "gas drainage" systems.

According to a study by CSIRO and the Australian Greenhouse Office, China's coal industry is the world's largest source of mine methane emissions, responsible for around 45per cent. The industry is expanding rapidly, and in 2003 China achieved a new record in coal production of 1608 megatonnes, a 15.4per cent increase from the previous year.

But a new CSIRO technology called VAMCAT (ventilation air methane catalytic turbine) could help to cut China's methane emissions, if it can attract a commercial partner to fund and fast-track construction.

CSIRO Mining and Technology are completing the design of a prototype gas turbine that will capture and use methane emissions from underground coal mining to generate green power.

A chemical engineer with CSIRO Sustainable Mining Systems, Andrew Beath, said a pilot-scale demonstration turbine could be operating at a coal mine in China within the next five years.

"It's still early days, but once we're able to build and demonstrate it, we should be able to convince a commercial partner that it's viable. It's a very simple device, not high-tech and easy to install - perfect for China's coal mines."