First published in the New Scientist 25 February 2012.
I once hitched a lift from New York to London in the private jet of an American gas billionaire. Robert Hefner III, who pioneered the drilling of deep wells in the 1960s, was planning to write a book and wanted to discuss it.
The Grand Energy Transition would argue that natural gas will solve “peak oil”, when global oil production starts to decline, and dramatically cut US emissions of greenhouse gases. Abundant and clean, gas offered a perfect bridging fuel to a future of limitless low-carbon energy based on hydrogen.
That was five years ago, with gas prices approaching near-record highs, so I was sceptical to say the least. But these days the US is awash with cheap, newly producible shale gas, and enthusiasts claim this “revolution” can be repeated around the world. So could it be that Mr Hefner, despite his obvious commercial interest, was right all along?
There is certainly far more gas around than most thought possible just a few years ago. Much of it comes from shale – petrified mud that was often rich in organic matter. Time, heat and pressure turned that organic content into oil and gas. In the past decade, the development of hydraulic fracturing, or “fracking”, has enabled gas companies to smash cracks deep underground that allow the trapped gas to flow back into the well. Fracking has raised US shale gas production from negligible levels in 2000 to 142 billion cubic metres in 2010 — nearly 20 per cent of US annual consumption. Other countries are now looking hopefully at their own shale deposits.
Investing in gas has certainly helped cut emissions in the past. In the 1990s, Britain switched away from coal to gas for generating electricity and reduced CO2 emissions from the power sector by 22 per cent over the decade. It’s no surprise then that some commentators have seized upon shale gas as an alternative to wind turbines, which they condemn as costly and unreliable.
And the benefits of gas need not be restricted to electricity generation, say its supporters. The Pickens Plan, devised by another US gas tycoon, T. Boone Pickens, is a scheme to replace petrol and diesel in transport. With compressed natural gas (CNG) selling for half the price of diesel, “we’re fools not to do it”, Pickens says. The benefits extend beyond the environmental: replacing oil imports with domestically produced gas would be good for energy security and the economy.
So if gas is newly abundant, low carbon and offers an alternative to scarce oil as a transport fuel, perhaps it really can cut greenhouse emissions and save the world?
On the face of it, the arguments for gas as a transport fuel are seductive. Hefner claims that swapping oil for CNG cuts CO2 emissions by up to 30 per cent, and converting the world’s vehicles would represent “a very large step forward in reducing global CO2 emissions”. He asserts that gas-powered vehicles like the Honda Civic “will always be much greener” than plug-in hybrid electric vehicles, such as the Chevrolet Volt, so long as they get much of their electricity from coal-fired power stations.
But do the figures back up his case? According to data from the US Argonne National Laboratory, over its lifecycle — from “well to wheels” — petrol emits 334 grams of CO2 equivalent for every kilowatt-hour of energy it contains, compared with CNG’s 297 grams. And according to figures from the US Environmental Protection Agency, the petrol and CNG versions of the Honda Civic achieve identical mileage per kWh. That means the emissions of the CNG car are 278gCO2e per mile, just 11% lower than those of the petrol version.
By contrast, a plug-in hybrid draws energy from the grid, which in the US pumps out a whopping 755 gCO2e/kWh, so like Mr Hefner you might assume the Volt’s emissions would be commensurately higher. But electric motors transform the picture because they are much more efficient than internal combustion engines. In all-electric mode, the Volt travels two and three quarter miles on one kilowatt hour – equivalent to 93 miles per US gallon – and that means its emissions are just 273 gCO2e /mile, fractionally lower than a CNG-powered Civic. The all-electric Nissan Leaf does better still, emitting 257 gCO2e/mile – 8% less than the CNG Civic.
So Mr Hefner’s contention does not stand up. The emissions from electric vehicles are already lower than those from CNG-powered cars. What’s more, if the Leaf is charged up in Europe — where grid power emits less carbon than in the US — the Leaf’s emissions fall to around 160 gCO2e/mile – 43 per cent lower than the Civic CNG. This shows that emissions from electric cars will continue to fall as electricity generation gets cleaner.
By contrast, CNG is a dead end for reducing emissions. Even if Mr Hefner’s 30 per cent cut in emissions could be delivered, the remaining 70 per cent would continue to spew from exhaust pipes. “By far the best way to eliminate tailpipe emissions is to eliminate tailpipes”, says Gary Kendall, a former Exxon chemist who wrote the 2008 report for WWF called Plugged In:The End of the Oil Age. “That means switching to electric cars, which get cleaner along with the electricity mix, and are the only vehicles capable of eliminating their emissions altogether”.
Another implication of the emissions data is that it would make more sense to burn natural gas in power stations and run electric vehicles on the electricity they produce than to compress the gas and burn it in car engines. This might suggest that natural gas can still save civilization — or at least start to — by displacing coal in power plants. But here again the picture is not as simple as the gas industry and its supporters would have us believe.
One reason is that gas may not be as clean as many people think. Methane is a more potent global warming gas than CO2, and plenty of it is released inadvertently from wells. These “fugitive” emissions make a big difference to the life-cycle emissions of natural gas.
Robert Howarth and his team at Cornell University in Ithaca, New York, analysed official emissions data from conventional gas wells and five fracked wells. They found methane emissions from unconventional wells are at least 30 per cent higher than those from regular wells and may be more than 100 per cent higher (Climatic Change Letters, vol 106, p 679).
Fracking involves pumping water and chemicals at high pressure into shale to crack the rock. Much of the fluid returns to the surface in the following weeks, before the well is sealed and a pipeline installed. With the fluid comes methane, and Howarth estimates that these emissions can amount to 1.9 per cent of a well’s total output. Subsequent leaks from pipework further downstream can raise total fugitive emissions to as much as 8 per cent of a well’s production over its lifetime. These downstream losses are shared by conventional gas production.
Next, Howarth and his colleagues compared the greenhouse gas footprint of natural gas with those of oil and coal. They concluded that over 20 years, shale gas emits up to twice as much CO2-equivalent as coal for each unit of energy it contains. Even when allowing for the greater efficiency of gas-fired power stations over coal-fired, electricity from shale gas could still release as much as 40 per cent more CO2-equivalent than coal. Gas from conventional wells did not fare much better. These findings “certainly call into question the idea of using shale gas as a bridging fuel”, says Howarth.
The research provoked an outcry from the gas industry and some academics. The quality of the data is poor, they argue, the 20-year timescale is too short and Howarth’s team has assumed that methane is a more potent greenhouse gas than it really is. Howarth accepts that emissions figures are scarce and approximate but says they are the best available.
He defends his work against the other criticisms. For example, according to the Intergovernmental Panel on Climate Change (IPCC), methane’s potential to warm the atmosphere is 72 times that of CO2 over 20 years, but because it stays in the atmosphere for only one-tenth as long as CO2, this potential falls to 25 times over 100 years. Howarth, however, uses values of 105 and 33, respectively, which include an added effect that methane has in the atmosphere: it reduces the concentration of aerosols, tiny particles that cool the planet.
And whereas many climate scientists stress the 100-year time frame, Howarth emphasises the 20-year period because of the need to start reducing greenhouse gas emissions in the coming decades. Cutting methane emissions now would have an earlier impact on global temperatures than cuts in CO2, he argues, and that would give more time for cuts in CO2 to take effect. “Without controlling methane we’re in a lot of trouble,” he says.
The true state of affairs over shale gas emissions and how to interpret their impact is still disputed. Although Howarth’s paper is the first peer-reviewed report on methane emissions from shale gas, other studies using the IPCC values for global warming potential and a 100-year time frame come up with far lower life-cycle emissions from shale gas, though all of them show that they are increasing the emissions from natural gas generally. Last year the EPA upped its estimate of fugitive emissions. A study by Deutsche Bank and the Washington DC-based research organisation Worldwatch Institute shows this revision increases the life-cycle greenhouse gas emissions of electricity produced from gas, but only to a level that is half that emitted by electricity generated from coal.
Fugitive emissions from shale gas wells could be much reduced with equipment to capture them at the well site, and the EPA has proposed a regulation that would encourage this. In a critique of Howarth’s paper, Lawrence Cathles, who is also at Cornell University, says that measures to reduce fugitive emissions are already in place (Climatic Change, DOI: 10.1007/s10584-011-0333-0).
But it is not happening everywhere. Earlier this month, it emerged that scientists monitoring air quality north of Denver, Colorado, were surprised to find high levels of natural gas and tracked them down to unconventional wells in the nearby Denver-Julesburg basin. The researchers from the US National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado, Boulder, estimate that the wells are leaking 4 per cent of their gas into the air.
“There is twice as much gas in the atmosphere compared with what the state and industry expect,” says Gabrielle Pétron, who works for both the university and NOAA. She thinks the team’s findings, which are soon to be published in the Journal of Geophysical Research, complement Howarth’s but stresses that more measurement is needed.
Yet in one sense, the exact level of emissions from unconventional wells is irrelevant: even if all natural gas turns out to be as “clean” as conventional gas is generally believed to be, it still could not deliver the emissions cuts proposed by climate scientists to avoid dangerous climate change.
One reason is that global demand for energy is so strong that the notion that gas will “displace” coal for generating electricity now looks fanciful. In the US and China, the world’s biggest polluters, coal and gas consumption are both forecast to increase over the next twenty-five years. So at best increasing gas production will reduce the rate of growth in emissions from coal, but will not reduce them in absolute terms. “In a world that is clamouring for energy”, says Kevin Anderson, professor of energy and climate change at the University of Manchester, UK, “exploiting a new resource like shale means emissions will rise, not fall”.
Even for nations where energy use is not growing steeply, where displacing all coal with gas might seem sensible, this strategy cannot deliver climate targets. Take the European Union, for example. To ward off dangerous climate change, it wants greenhouse gas emissions cut by 80 per cent of 1990 levels by 2050. To hit this target, the UK government’s Committee on Climate Change calculates that average emissions from British electricity need to fall from around 500g/kWh today to 50g/kWh by 2030. Yet the most efficient gas plants emit around 440g/kWh, so gas might reduce emissions in the short term, but would make later targets harder to hit.
They could also make it more expensive, according to a report from the Green Alliance thinktank, entitled ‘Avoiding Gas Lock-in: why a second dash for gas is not in Britain’s interest’. The report warns that so much gas fired plant is either under construction or being planned that power stations worth ₤10 billion will have to be retired early if emissions targets are to be achieved in the 2020s. Author Dustin Benton says in future, gas power stations will have to operate as ‘peaking’ plant, generating only a few hours per year, or be fitted with expensive carbon capture and storage (CCS) technology, which is not yet commercially available.
Clearly, the case for natural gas as a bridging fuel to a low-carbon future is far weaker than the industry would have us believe. It’s certainly no panacea for our energy problems. If used widely in transport and unabated electricity generation, gas could prevent countries from achieving legally binding climate targets, and allow emissions to continue to soar.
Some conclude that risk is too great. Last November, Anderson contributed to a report by the Tyndall Centre for Climate Change Research into the potential of shale gas for the UK. It concludes that “shale gas offers no meaningful potential as even a transition fuel”. Developing shale gas now is likely to prove “economically unwise or risk jeopardising the UK’s international reputation on climate change”. Far better, it argues, to go for the grand prize and invest in very low carbon energy technologies.
None of which will deter the gas industry from continuing to insist that “natural gas is truly the bridge fuel to civilization’s sustainable future”, in the words of Robert Hefner. But perhaps that’s no surprise. After his private jet touched down in the UK, Mr Hefner was quickly on the phone to a drilling rig that was about to penetrate a new gas reservoir. The value of gas it was expected to produce? $8 billion.