Methane is a strong absorber of infrared (heat) radiation leaving the Earth’s atmosphere, and thus implicated in the ongoing global warming of our planet. After a lull in the 1990s, the concentration of methane in the atmosphere began rising rapidly in 2006. Methane levels hit an all-time high last year. Scientists are uncertain of the recent emissions of methane, which must be rising. Some believe that the increasing emissions are due to greater emissions from wetlands, both in the tropics and far northern latitudes. Others believe that the recent rise in methane in the atmosphere is due to the recent proliferation in the use of natural gas as a fuel and in the advent of hydraulic fracking to produce it.
It is worth examining these suggestions in a little detail, but bear with me as we pursue some chemistry. (I’ll try to make it simple). Methane is a molecule with four hydrogen atoms attached to one central carbon atom. The carbon in methane can have several isotopic forms, for example, carbon-12 or carbon-13, which has an extra neutron in its nucleus. Measured against a laboratory standard, methane in the atmosphere has an isotopic ratio (13C to 12C) of about -47 parts per thousand parts, abbreviated ‰, relative to the standard. Methane from natural gas has a higher ratio—about -20‰, whereas methane from wetlands is about -60‰. In recent years, the methane in the atmosphere has fallen from -47.2 to -47.4, implying that changes in the atmosphere must be due to increasing emissions from wetlands. Methane from natural gas would pull the ratio in the opposite direction.
Emissions of ethane are associated with natural gas, and the concentration of ethane was stable or falling in Earth’s atmosphere during the period when methane was relatively constant. In recent years, the concentration of ethane has started to increase, suggesting greater emissions of natural gas as the source of rising methane in Earth’s atmosphere—a conclusion opposite that derived from the isotopes.
Several recent studies have suggested that we have underestimated the emissions of methane from the production and global supply network for natural gas. But, as much as fracking is in the news, we cannot make the immediate leap that greater use of natural gas is now responsible for the current increase in methane in the atmosphere. First, even if the leakage from the natural gas supply chain has been underestimate by 40%, that does not mean that the emissions are now 40% greater than a few years ago—only that they are 40% greater than what we previously thought, based on erroneous measurements. Indeed, the flux from natural gas could be constant, albeit poorly estimated.
Something on the order of 1 to 2 percent of the natural gas produced in the United States is lost due to leakage from the production system. This may have increased in recent years, but we have no consistent and long-term standard measuring system to substantiate that belief. It is potentially equally possible that the recent rise in methane in Earth’s atmosphere is largely dominated by increased production from high latitude, permafrost soils that are now melting due to global warming.
The popularity of natural gas as a fossil fuel and its increased use are attractive candidates to explain the potential for increased leakage to the atmosphere. That makes sense to me, but the jury is still out on whether this is a cause of the current rise in methane concentrations.
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2 thoughts on “The Methane Mystery”
As is your habit, you have hit upon another important facet of our world ecosystem. Regarding natural gas production, the intentional venting (release without burning) of natural gas at the wellhead could have been a major methane producer, as it was and still is common in natural gas wells. Does the rate of breakdown of natural gas in the atmosphere have any relationship to the isotopes comprising the gas?
Also has the production of rice increased in southeast Asia? I once read that rice paddies produce rather large quantities of methane. I wonder, is there research on how the global green revolution has altered our production of methane?
Secondly, methane seems to have played a major role in our planet’s past climates and in what species survive and thrive over the eons. Do you think there is enough research on methane as a paleontological planetary driver of ecosystems and weather? I read constantly about how methane is a major constituent of the larger planets in our solar system.
Great article. You have shined a light on a molecule which I believe has been understudied and as a consequence, under estimated.
Has anyone considered that BOTH natural gas (NG) emissions (as also indicated by ethane level increases) and wetlands emissions are large and increasing? As it relates to Carbon-13/carbon-12 ratios, these largely cancel one another. Your third reference indicates that radioactive Carbon -14/Carbon-12 ratios also indicate more NG emissions. Has anyone looked at carbon-14 ratios in atmospheric methane over tropical and high latitude thawing wetlands to distinguish their contributions?
A brand new paper is (2020) 10:4199 | https://doi.org/10.1038/s41598-020-61035-w
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