Burning methane (whether from shale gas or elsewhere) produces half as much CO2 per unit energy as coal. So switching from coal fired power stations to gas leads to significant reductions in CO2 emissions. This is why 5 to 10 years ago, every environmentalist was calling for a 'golden age for gas'.
However, methane itself is a potent greenhouse gas: 75 times more potent than an equivalent mass of CO2 over 20 year timescales, 20 times more potent over 100 years (the potency goes down over time because methane comes out of the atmosphere faster than CO2, meaning that if equivalent masses are released, the methane gets removed faster). So, if while extracting methane you end up releasing lots of it to the atmosphere, it can cause more warming than you save by burning gas instead of coal.
This was the suggestion made by Howarth, a professor at Cornell. Since then, the debate has rumbled on, with a number of rebuttals, including from Howarth's colleagues at Cornell. Nevertheless, I still see the 'shale gas is as bad as coal for the climate' line being trotted out regularly in news reports and discussions about shale gas.
However, I think the shale-gas and climate change issue can finally be put to bed. A new report for the European Commission has been produced, looking at the life-cycle greenhouse gas emissions for European shale gas. It runs to 158 pages, so I can't tell you I've read it all, but here are the highlights. These number are based on an assumption of a loss of 1 - 5% of the methane at the well head during the fracking process - generally accepted numbers for most people. So, what does that mean?
1.) Shale gas isn't as good as conventional European gas (i.e. from conventional fields, mainly in the North Sea and onshore Netherlands). GHG emissions from shale gas are 4% - 8% higher than conventional gas. But that was hardly surprising. However, our conventional gas fields are all beginning to run out.
2.) European shale gas may well be better than gas piped from Russia or Algeria, or shipped in as LNG. Obviously, it takes energy to transport gas from these distant places in to Europe, increasing the amount of GHG emitted per unit of energy you generate. So European shale gas has emissions 2% - 10% lower than piped Russian or Algerian gas, and 7% - 10% lower than gas imported as LNG. This is REALLY interesting - it says that if we plan to burn gas (even as a backup to large wind farms and solar), it should be our home-grown European shale gas, rather than gas imported from afar (not to mention the geopolitical implications of having to give Mr Putin et al all our money).
3.) Shale gas is significantly better than coal. Not surprising to people who have studied that numbers from previous studies, but hopefully if enough reports say this, I'll get to stop reading in newspapers and environmental publicity that shale gas is more dirty than coal. Emissions from shale gas-fueled electricity are 41 - 49% lower than emissions from coal. That's a really significant chunk we could take out of our GHG emissions just by switching from coal fired power to gas.
And is there evidence to back this up? There sure is! US CO2 emissions are plummeting as cheap shale gas displaces coal from the electricity generation market. While some of the 9% decrease in CO2 emissions can be attributed to improved efficiency reducing demand, and increased renewable energy sources, the major bulk (77% by John Hanger's estimate). Wouldn't it be nice if we could have cheaper energy bills while reducing our CO2 emissions over here in Europe?