Gas has worse climate footprint than coal

February 12, 2013

As the fossil fuel lobby tells it, natural gas — in chemical terms, almost all methane — is clean and green. Burn it in a modern power plant, and per unit of electricity produced, only about half as much carbon dioxide is sent up the exhaust stack compared to good-quality coal.

That’s like saying you’re making progress if you get off heroin onto amphetamines. Natural gas is still a fossil fuel. Even if the sums worked the way the gas corporations suggest, a wholesale switch to gas would put off climate disaster only by a few decades.

In any case, the real sums are quite different. When you extract and burn natural gas, you never get to burn all of it. Some escapes, meaning that the gas-fired electricity you produce will almost always have a worse “climate footprint”, over the most relevant period, than if you were using coal.

That statement would have seemed highly speculative just a few years ago. But methane has long been known to be a powerful greenhouse gas. Now, new studies are showing that in practical gasfield operations, far more methane reaches the atmosphere than the guesses of the energy corporations would suggest.

The worst leakage, it used to be thought, occurred with so-called unconventional sources — coal seam gas and shale gas. But “fugitive emissions” from conventional gasfields, evidence now shows, can also be alarmingly high.

And whatever the source of the methane leaks, recent research has substantially raised the estimate for their warming impact — to an astonishing 105 times the figure for carbon dioxide, measured over 20 years.

Three field studies, reported over the past year, have exposed the claims of the gas industry that its product has a role to play in limiting climate change.

All three of these studies use “top-down” methods to calculate methane leakage rates. Top-down methods sample methane concentrations in the air above gasfields, and use mathematical models to calculate the amount of methane that would need to have leaked to produce this effect. “Bottom-up” calculations, by contrast, examine the wells, valves and pipes, and try to total up the quantity of gas that is lost from them.

Top-down methods are complex, but yield a fairly robust figure for the emitted methane. With bottom-up calculations, leaks are inevitably missed. Of course, not all the methane detected above gasfields results from extraction operations; some has come from sources such as wetlands or cattle and sheep. But by observing the ratio of different carbon isotopes found in the methane molecules, scientists can tell “new” methane from fossil methane that has been underground for millions of years.

Colorado conventional

In 2008, geochemist Gabrielle Pétron of the US National Oceanic and Atmospheric Administration (NOAA) observed that methane readings in data from an observation tower north of Denver, Colorado, were markedly higher when the wind blew from the north-east — that is, from the direction of the Denver-Julesburg (conventional) oil and gas basin, with its more than 14,000 active gas and condensate wells.

Years of complex work followed, culminating in February last year with the publication by Pétron and colleagues of a paper concluding that leakage from the field was probably around 4% of the gas produced, and perhaps significantly higher.

That suggests leakage at least twice the rate earlier assumed. An October blog for the journal Nature explains: “Most estimates suggest that around 1-2% of the methane is lost… These [estimates] come from ‘bottom-up’ calculations by industry and government regulators, but there is very little hard data.”

The Pétron team’s findings were disputed in a peer-reviewed commentary published by the Journal of Geophysical Research in November. But preliminary results from a subsequent study, using isotopic analysis of methane emissions from the Denver-Julesburg field, now reportedly line up with the findings by Pétron and her collaborators.

Queensland coal seam

For the next blow against the fossil gas merchants, we need look no further than Southern Cross University in northern New South Wales. Importing a specialised spectrometer, biochemists Isaac Santos and Damien Maher drove to the Tara coal seam gas field on the western Darling Downs.

Over their 500 kilometre trip to Tara, the researchers recorded atmospheric methane figures of 1.78 to 1.94 parts per million. Those are typical present-day world background levels.

Once on the gasfield, the team drove back and forth on public roads, taking measurements every second and pinpointing them with GPS. “In Tara the concentrations are consistently higher than two parts per million and approach seven parts per million in a few locations,” Southern Cross University reported Maher as saying.

“This is about three and a half times higher than expected if there was no change in the atmosphere.”

“The concentrations are higher here than any measured in gasfields anywhere else that I can think of, including in Russia,” Maher told the Sydney Morning Herald.

The response from gas industry spokespeople was vitriolic. “The Australian Petroleum Production and Exploration Association … attacked the research, saying it was ‘premature and questionable’,” the SMH reported on November 14.

Federal Energy and Resources Minister Martin Ferguson thundered to an energy conference in Sydney that the study was “a cynical attempt to grab headlines” that “abandoned usual scientific practice.”

Isotopic analysis nevertheless showed that the elevated methane levels at Tara were due to geologic methane. A problem for the researchers is the lack of baseline data from the Tara field; the gas developers there did not record background methane levels before starting to drill.

But it is unlikely that natural seepage is an important factor in the high readings at Tara.
Observations near Lismore and Casino in the Richmond River basin, a prospective but still-undeveloped coal seam gas region, did not approach those at Tara — even near intensive cattle operations.

Utah: the Uinta Basin

The most recent findings to be released are from another intensive top-down study conducted in the US by scientists from the NOAA and the University of Colorado. This time, the target was the rich oil and gas fields of the Uinta Basin in eastern Utah.

During the winter of 2011-12 the scientists conducted an air and ground survey of the basin, taking readings of at least seven pollutant gases. Preliminary results were reported to a meeting of the American Geophysical Union in December 2012.

“Overall methane levels are very high (often >2.5 ppm) in the gasfield,” the NOAA said. Modelling of methane leakage in the Uinta Basin pointed to an “eye-popping” figure of 9% of total production. “That figure is nearly double the cumulative loss rates estimated from industry data,” a commentary in the journal Nature observed.

Home mostly to conventional oil and gas wells, the Uinta Basin is noted for a high rate of “fracking” — that is, hydraulic fracturing, in which drillers inject a high-pressure mix of water, sand and chemicals to open fissures in underground rocks to speed oil and gas flow.

Often used in conventional oil and gas extraction, fracking is also frequently used in production of coal seam gas, and is fundamental to the rapidly-expanding shale gas industry. The technique is particularly associated with high gas releases during drilling, since an estimated 30-70% of the injected water resurfaces, bringing gas with it.

Fracking can also open alternative routes for gas to reach the surface via rock faults, bypassing the well and its collection mechanisms. This may partly explain the striking divergence between top-down and bottom-up figures for gas leakage.

Significantly, the figures for gas leakage in the Denver-Julesburg and Uinta Basins are within or above the range indicated in 2011 by the first serious attempt to quantify emissions from shale gas extraction. Conducted by a team under Cornell University scientist Robert Howarth, this study put leakage from the shale gas industry in the US at 3.6-7.9%.

Howarth’s findings were derided by energy industry spokespeople who pointed to the study’s limited data sample. But the new work suggests that Howarth’s figures were, if anything, conservative.

Warming Effects

Meanwhile, what exactly are the warming effects of methane once it reaches the atmosphere?
Methane in the air oxidises relatively quickly to carbon dioxide and water. Almost all of it is gone within twenty years of its release.

Usually, the gas is described as having a warming impact per molecule 20-25 times that of carbon dioxide, measured over 100 years. But this 100-year measure is only a convention, and an inept one at that. Climate change is moving much faster than expected. Over as little as a decade, a big pulse of methane from unconventional gas development could help push the climate past “tipping points” such as the collapse of Arctic sea ice or Amazonian forests.

On a 20-year time-frame, methane is cited as having a warming footprint 72-79 times that of carbon dioxide. And that’s not the whole story. In the atmosphere methane interacts with aerosols, ultrafine airborne particles. NASA scientist Drew Shindell, who studies these reactions, calculates that when they’re taken into account methane has a 20-year climate impact 105 times that of carbon dioxide.

If methane leakage is just 1%, that means, gas-fired electricity has a 20-year warming effect roughly equal to black coal. And leakage in the Uinta Basin has now been put at 9%.

What’s worse than heroin addiction, quicker and far more drastic in the damage it wreaks? Drinking methylated spirits? That’s the sort of grim metaphor we have to invoke if we’re to describe the potential impacts of the fossil gas industry.

Relate article: White paper reveals gas industry scared of global protests

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