Newcastle Greens spokesman John Sutton said the Cornell University study showed more work was needed before Eastern Star Gas was allowed to mine coal-seam gas in western NSW for export through Newcastle.

Cornell environmental biologist Professor Robert Howarth says his work on shale gas is relevant to Australian coal-seam gas, which he says is a similar product extracted using similar methods.

Eastern Star spokesman Peter Fox said the industry-funded Energy in Depth group had found holes in Professor Howarth's calculations.

Professor Howarth said his work was peer-reviewed and his critics either worked in the industry or had been funded to promote it.

Writing in the April edition of the Climactic Change journal, Professor Howarth and his team say "the footprint for shale gas is greater than that for conventional gas or oil when viewed on any time horizon, but particularly so over 20 years".

"Compared to coal, the footprint of shale gas is at least 20 per cent greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years."

Mr Fox said a Worley Parsons report published last month said coal-seam gas as a short-term peaking fuel in an efficient closed-cycle turbine produced up to 87 per cent less greenhouse gas than coal.

But as a baseload fuel in a simple open-cycle, turbine gas was as little as 5 per cent more efficient than coal.

It found that 94 per cent of the greenhouse gas emissions from export coal would be released when combusted in the importing nation. In contrast, 22 per cent of coal-seam gas emissions were released during mining and transport in Australia.