Posted on Friday, March 30th, 2012
First published at New Scientist, 30 March 2012.
Coverage of the gas leak at Total’s Elgin platform in the North Sea, off the UK coast, has so far focused on the potential for an explosion, and damage to sea life from hydrogen sulphide contamination – the latter now discounted. But methane is a powerful greenhouse gas, so what about the global warming impact? Here’s what emerged from the back of my envelope.
A company spokesman is reported as saying about 200,000 cubic metres is escaping per day, based on the plume visible above the platform. Of that, around 90 per cent or 180,000 m3 is likely to be methane, according to gas expert John Baldwin, of CNG Services. Total says it may take six months to drill a relief well to plug the original, so if the leak continues at its estimated rate, 32,760,000 m3 of methane would be emitted altogether. At about 1500 m3 per tonne, that amounts to roughly 22,000 tonnes of methane. What would that mean in warming terms?
The standard global warming potential of methane is 25 over 100 years, meaning it has 25 times the warming effect of carbon dioxide over that period. So 22,000 tonnes of methane is the equivalent of 550,000 tonnes of CO2. That’s more than twice the annual emissions of the power station at the Sullom Voe oil terminal in Shetland, according to figures from the EU Emissions Trading Scheme.
However, scientists attribute methane with a much higher global warming potential over shorter periods, because it persists in the atmosphere for much less time than CO2, so its impact is concentrated in the early years. The IPCC’s 20-year global warming potential is 72, and on that basis the Total leak would emit the equivalent of 1,584,000 tonnes of CO2 over six months. That’s almost four times the annual emissions of the Lafarge cement works at Dunbar, and more than a year’s worth of CO2 from RWE’s power station at Staythorpe in Nottinghamshire, which serves almost 3 million homes.
Recent research has suggested methane should have an even higher short term global warming potential of 105, because it reduces the concentration of aerosols that cool the atmosphere. That would raise the emissions of a 6 month leak from Total to just over the equivalent of 2.3 million tonnes of CO2 – roughly equal to the 2010 emissions of the massive Teesside Power Station. At 1875MW Teesside was – until its partial shutdown in 2011 – the largest combined cycle gas turbine power station in Europe, capable of supplying 3 per cent of UK’s electricity needs.
Of course, the Total leak might turn out to be smaller than 200,000 m3 per day, or it could be fixed in less than 6 months. But if the BP Deepwater Horizon oil spill in the Gulf of Mexico in 2010 is anything to go by, early estimates of the size of the leak from the operator may turn out to be a massive underestimate.
No wonder Michael Liebreich, chief executive of Bloomberg New Energy Finance, has tweeted suggesting Total should be obliged to buy carbon offsets to compensate for the emissions.