I FIRST heard the idea on a private jet flying from New York to London. The US oil billionaire Robert Hefner III, known as the “father of deep natural gas”, had offered me a lift to discuss a book he was planning. The idea was, perhaps unsurprisingly, that natural gas will solve the supply problem of “peak oil” – when global oil production starts to decline – and dramatically cut US emissions of greenhouse gases, making it a perfect bridging fuel to a low-carbon future.
With gas prices approaching record highs at the time, I was sceptical to say the least. But things have changed. Today the US is awash with cheap gas, thanks in part to the newfound ability to extract large amounts of shale gas. So could it be that Hefner, despite his obvious commercial interest, was right all along?
Fellow tycoon T. Boone Pickens has also been pushing the gas agenda and their ideas have found enthusiastic support among the US public and in Congress. Replacing oil imports with domestically produced gas may promise better energy security and economic benefits. Is it the best route for cutting carbon emissions, though? Natural gas, which is mainly methane, may generate less carbon dioxide than oil and coal when burned, but as recent research has found, there’s more to greenhouse gas emissions than just combustion.
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There is certainly far more gas around than seemed possible just a few years ago. Much of it comes from shale, deep petrified mud rich in organic matter that time, heat and pressure have turned into oil and gas. In the past decade, the development of hydraulic fracturing, or “fracking”, has enabled gas companies to break open cracks in the rock through which the gas escapes into the well. Conventional gas reserves are porous and don’t need such cracks. Fracking has raised US shale gas production from negligible levels in 2000 to 142 billion cubic metres in 2010 – nearly a fifth of annual consumption. Other countries are now looking hopefully at the rocks beneath them.
Converting to gas has cut emissions in the past. In the 1990s, the UK began switching from coal to gas for generating electricity and reduced CO2 emissions from its 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.
Making it happen
The benefits of gas need not be restricted to electricity generation, say its supporters. Pickens has even devised , 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. He and others have poured $1 billion into building CNG fuelling stations and they are lobbying Congress to pass a bill to subsidise natural gas vehicles.
Hefner’s book, The Grand Energy Transition, was eventually published in 2009, and in it he claims that replacing petrol and diesel with CNG in cars cuts CO2 emissions by up to 30 per cent. Converting the world’s vehicles would represent “a very large step forward in reducing global CO2 emissions”. He asserts that vehicles running on CNG, such as the Honda Civic Natural Gas “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 the US Argonne National Laboratory, over its life cycle – from source to use – petrol emits 334 grams of CO2 equivalent (gCO2eq) for every kilowatt-hour of energy it contains, compared with CNG’s 297 grams. And according to figures from the US Environmental Protection Agency (EPA), the petrol and CNG versions of the Honda Civic travel the same distance per kWh. That means the emissions of the CNG car are 173 gCO2eq per kilometre, 11 per cent lower than those of the petrol version (see diagram).
By contrast, a plug-in hybrid draws energy from the grid, which in the US pumps out a whopping 755 gCO2eq/kWh, so like Hefner you might assume that 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 is responsible for emissions of 168 gCO2eq/km, which is fractionally lower than a CNG-powered Civic. The all-electric Nissan Leaf does better still, accounting for just 160 gCO2eq/km.
So even now gas cannot match electricity for cutting emissions from cars. What’s more, if the Leaf is charged up in Europe – where – the Leaf’s emissions fall to 99 gCO2eq/km. And emissions from electric cars will keep falling as power generation gets cleaner.
CNG, however, is a dead end for reducing emissions. Even if Hefner’s 30 per cent cut in emissions could be delivered, methane burns to produce CO2, so 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 now working at the Cambridge Programme for Sustainability Leadership in South Africa. “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 makes more sense to burn natural gas in power stations and run 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 help to cut emissions by displacing coal in power plants. But here again the picture is not as simple as the gas industry 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.
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 ().
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 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), 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. 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, ).
Unexpected releases
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 , 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 of gas “displacing” coal for generating electricity now looks fanciful. In the US and China, the world’s biggest polluters, both coal and gas consumption are forecast to rise over the next 25 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, exploiting a new resource like shale means emissions will rise, not fall,” says , a professor of energy and climate change at the University of Manchester, UK.
“Demand for energy is so strong that the notion of gas ‘displacing’ coal now looks fanciful”
Even where energy use is not growing steeply, where displacing all coal with gas may seem sensible, this strategy is unlikely to deliver emissions targets. Take the European Union. To ward off dangerous climate change, it wants greenhouse gas emissions cut by 80 per cent of their 1990 levels by 2050. According to the Committee on Climate Change, which advises the UK government, this means CO2 emissions from electricity need to fall from around 500 g/kWh today to 50 g/kWh by 2030. The most efficient gas plants emit around 440 g/kWh, so gas might reduce emissions in the short term, but would make later targets harder to hit.
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 problems with greenhouse gas emissions.
Some conclude that it is no solution at all. Last November, Anderson contributed to 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 [will] 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.
Of course, none of this deters the gas industry from its crusade. After his private jet touched down in the UK, 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.
