Natural gas is a much “dirtier” energy source, in terms of carbon, than we thought


At the height of a summer of fieldwork in Greenland in 2015, Benjamin Hmiel and his team drilled into the frozen bowels of the immense ice cap, periodically lifting a chunk of crystalline ice the size of an engine. motorbike. The ice contained part of the answer to a question that has pestered scientists for years: How much of the methane in the atmosphere, one of the most powerful sources of global warming, comes from the oil and gas industry?

Previously, geological sources like volcanic seeps and gaseous mud pots were thought to spew about 10 percent of the methane that entered the atmosphere each year. But new research, published this week in Nature, suggests that natural geological sources make up a much smaller fraction of the methane in today’s atmosphere. Instead, the researchers say the methane is most likely attributable to industry. In total, the results indicate that we have underestimated the methane impacts of fossil fuel extraction by up to 40%.

This is both bad and good news for climate change, says Hmiel, lead author of the study and researcher at the University of Rochester. Bad, because it means oil and gas production had a messier and bigger impact on the greenhouse gas budget than scientists thought. But Hmiel finds the result encouraging for almost the same reason: the more methane emissions that can be attributed to human activities like oil and gas extraction, the more it means that policymakers, businesses and governments. regulators need to control the problem.

“If we think of the total methane in the atmosphere like slices of a cake, one slice comes from ruminants, the other from wetlands. The slice that we thought was coming from geological methane was too large, ”explains Hmiel. “So what we’re saying is that the fossil fuel pie share is bigger than we thought, and we can have a bigger influence on the size of the share, because that’s something that we can control. “

Methane, the fuel for the “bridge”, but a bridge to where?

A powerful greenhouse gas, methane’s carbon core and hydrogen arms are arranged in a configuration that makes it exceptional for absorbing heat. On a 20-year timescale, a methane molecule is about 90 times more effective at trapping heat in the atmosphere than a molecule of carbon dioxide, the greenhouse gas that most controls future warming in the world. Earth in the long run.

Atmospheric concentrations of methane have increased by at least 150% since the industrial revolution. Because of its potency, the more of it in the air, the harder it will be to keep global temperatures from exceeding global climate targets.

Methane is also the protagonist of a scientific mystery that has lasted for decades on a global scale: where exactly does all the extra methane that warms the atmosphere today come from? Is it cow burps or rice fields? Leaks from oil and gas production? Bubbling gaseous mud volcanoes or seeps along the changing seams of the Earth?

In recent decades, as calls for reduced carbon dioxide emissions have grown and natural gas harvesting technologies such as hydraulic fracturing have become cheaper, many coal-fired power plants in the United States have become less expensive. United and abroad have retired. In the United States, more than 500 coal-fired power plants have closed since 2010. In many cases, they are being replaced by natural gas plants (made up mainly of methane), which now produce nearly 40% of the states’ energy needs. -United.

Methane burns more efficiently than coal, making it a better option, in terms of carbon cost and air pollution, than coal. It also stays in the atmosphere much shorter than CO2 – an average of nine years, relative to CO.2‘s hundreds.

Due to its characteristics, natural gas has often been touted as a “transitional fuel” to facilitate the transition to a carbon neutral energy future. Natural gas power plants now meet energy needs while renewable or carbon-negative technologies are developing.

“The question is, is it a bridge fuel, or is it going to be there for a very long time? says Sheila Olmstead, an environmental economist at the University of Texas at Austin. “The market tells us it’s probably going to be there for a long time.”

However, the climate cost of natural gas is based on a basic assumption: there are less total carbon emissions from natural gas than from other sources. But in recent years, a flotilla of scientific studies has challenged this assumption, primarily by examining how much gas is lost in the production process.

If there are very few leaks or losses along the way (less than a few percent of the total amount of gas recovered), the calculations are perfect. But if this “leak rate” exceeds about 1% of the total gas recovered, the budget becomes hazy, says Robert Howarth, climatologist at Cornell.

A recent study found that the “leakage rate” of gas widely used in the natural gas production process in the United States could exceed 2%. Others, when examining specific “super transmitters” in major US drilling regions, have found even more leaks.

“In the last few years of research, I would say the whole argument for methane as a bridge fuel has really faded,” Howarth explains. “But if we go back and say we really need natural gas for a while, that calculation depends on the break-even point of methane. And we’re not sure we’re close.

Phase out CO2 emissions is essential, emphasizes Jessika Trancik, an energy expert at MIT, because that’s what will keep the planet locked in for long-term warming. But for the climate goals the world is striving to achieve right now – preventing air temperatures from skyrocketing the Paris Agreement’s 3.6 degrees Fahrenheit (2 degrees Celsius) temperature targets 2015 – it is also essential to prevent any excess methane from escaping into the atmosphere.

“You can’t achieve these climate goals with methane in the mix,” says Lena Höglund Isaksson, greenhouse gas expert at the Austrian International Institute for Applied Systems Analysis.

(See methane leaking from a leak in a natural gas storage field near Los Angeles).

Ice has answers

It is remarkably difficult to determine how much of the methane in the atmosphere comes from human sources, like drilling or burning oil and gas, how much comes from other human-influenced sources like agriculture, and how much. comes from natural sources such as volcanic seeps.

Where it comes from determines what humans can do about it. If it’s oil and gas, we can fix the systems to produce less. If they are volcanoes, we might be less able to manage the emissions.

“It’s like a detective story,” explains Höglund Isaksson.

In the past, scientists have estimated the amount of so-called natural methane from geological sources by walking to a weeping or muddy volcano and measuring its emissions very carefully. Then scientists would scale up those observations to make an estimate for the entire planet. Using this strategy, most estimates put the annual contribution of methane from natural geology at about 50 teragrams per year, or about 10 percent of the total annual amount of methane emitted. Recent estimates place the total annual contribution of methane from the acquisition and combustion of fossil fuels at just under 200 teragrams.

Hmiel’s team suspected that the geological sources might actually be even smaller – and they had a place to test that suspicion: the vast, flat Greenland ice cap. The ice there, buried more than 100 meters below the surface, pre-date the start of the Industrial Revolution in the 1800s, so there was pre-industrial methane trapped in tiny air bubbles in its network. frozen.

They dug up over 2,000 pounds of ice. Then, they sucked air containing methane from the bubbles trapped in the ice.

Methane from natural geological sources has a slightly different chemical composition than methane from other sources, such as wetlands. The methane sucked from the 250-year-old ice contained only traces of a tiny amount of geological methane. And because the samples were from before the start of the Industrial Revolution and the concomitant increase in methane from coal and oil, there was no trace of methane from fossil fuels.

In contrast, samples after the start of the Industrial Revolution showed a telltale footprint of fossil fuels.

But the main finding was the small amount of methane from geological sources in the ice: the equivalent of no more than about 5 teragrams of methane released into the atmosphere per year, in these fossil fuel-dependent days. The geology is unlikely to have changed in such a short time, so this estimate is, according to Hmiel, a good guess about the contribution of geology today as well.

Importantly, this contribution is 10 times lower than other estimates, including those used by the United States Environmental Protection Agency and the Intergovernmental Panel on Climate Change, used to make scientific assessments and political decisions.

Overall, scientists have long known exactly how much methane there is in the atmosphere. That number has not changed: there are still around 570 teragrams of methane that accumulate in the atmosphere each year. But if there are far fewer natural geological sources, another source must make up the difference. The team could also demonstrate that the most likely source is oil and gas development.

While oil and gas operations have had a much larger footprint on methane emissions than previously thought, Hmiel thought, it also means they can clean up those emissions – both by reducing the amount of gas. used and cleaning up leaks, torches and the like. wasted gas from the process.

“Electric utilities that currently choose to focus on wind and solar or gas – if they choose gas, it’s critical to understand that this plant is going to be around for decades,” says Olmstead.

“They have real endurance well beyond the nameplate expiration date. Knowing this, does it change the decisions we make today? That we will have effects on methane emissions in 10, 20, 30, 40 years?


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