Global Science Report is a feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”
Methane is all the rage. Why? Because 1) it is a powerful greenhouse gas, that molecule for molecule, is some 25 times as potent as carbon dioxide (when it comes to warming the lower atmosphere), 2) it plays a feature role in a climate scare story in which climate change warms the Arctic, releasing methane stored there in the (once) frozen ground, which leads to more warming and more methane release, ad apocalypse, and 3) methane emissions are also be linked to fossil fuel extraction (especially fracking operations). An alarmist trifecta!
Turns out, though, that these favored horses aren’t running as advertised.
While methane is a more powerful greenhouse gas in our atmosphere than carbon dioxide, its lifetime there is much shorter, even as the UN’s Intergovernmental Panel on Climate Change can’t quite say how long the CO2 residence time actually is. This means that it is harder to build-up methane in the atmosphere and that methane releases are more a short-term issue than a long-term one. If the methane releases are addressed, their climate influence is quickly reduced.
This is why methane emissions from fracking operations—mainly through leaks in the wells or in the natural gas delivery systems—really aren’t that big of a deal. If they can be identified, they can be fixed and the climate impact ends. Further, identifying such leaks are in the fracking industry’s best interest, because, in many cases, they represent lost profits. And while the industry says it has good control of the situation, the EPA isn’t so sure and has proposed regulations aimed at reducing methane emissions from new and existing fossil fuel enterprises. The recent scientific literature is somewhat split on who is right. A major paper recently published in Science magazine seemed to finger Asian agriculture as the primary suspect for recent increases in global methane emissions, while a couple of other recent studies seemed to suggest U.S. fracking operations as the cause (we reviewed those findings here).
And as to the runaway positive feedback loop in the Arctic, a new paper basically scratches that pony.
A research team led by University of Colorado’s Colm Sweeney set out to investigate the strength of the positive feedback between methane releases from Arctic soil and temperature (as permafrost thaws, it releases methane). To do this, they examined data on methane concentrations collected from a sampling station in Barrow, Alaska over the period 1986 through 2014. In addition to methane concentration, the dataset also included temperature and wind measurements. They found that when the wind was blowing in from over the ocean, the methane concentration of the air is relatively low, but when the wind blew from the land, methane concentration rose--at least during the summer/fall months, when the ground is free from snow and temperature is above freezing. When the researchers plotted the methane concentration (from winds blowing over land) with daily temperatures, they found a strong relationship. For every 1°C of temperature increase, the methane concentration increased by 5 ± 3.6 ppb (parts per billion)—indicating that higher daily temperatures promoted more soil methane release. However (and here is where things get real interesting), when the researchers plotted the change in methane concentration over the entire 29-yr period of record, despite an overall temperature increase in Barrow of 3.5°C, the average methane concentration increased by only about 4 ppm—yielding a statistically insignificant change of 1.1 ± 1.8 ppm/°C. The Sweeney and colleagues wrote:
The small temperature response suggests that there are other processes at play in regulating the long-term [methane] emissions in the North Slope besides those observed in the short term.
As for what this means for the methane/temperature feedback loop during a warming climate, the authors summarize [references omitted]:
The short- and long-term surface air temperature sensitivity based on the 29 years of observed enhancements of CH4 [methane] in air masses coming from the North Slope provides an important basis for estimating the CH4 emission response to changing air temperatures in Arctic tundra. By 2080, autumn (and winter) temperatures in the Arctic are expected to change by an additional 3 to 6°C. Based on the long-term temperature sensitivity estimate made in this study, increases in the average enhancements on the North Slope will be only between -2 and 17 ppb (3 to 6°C x 1.1 ± 1.8 ppb of CH4/°C). Based on the short-term relationship calculated, the enhancements may be as large as 30 ppb. These two estimates translate to a -3 – 45% change in the mean (~65 ppb) CH4 enhancement observed at [Barrow] from July through December. Applying this enhancement to an Arctic-wide natural emissions rate estimate of 19 Tg/yr estimated during the 1990s and implies that tundra-based emissions might increase to as much as 28 Tg/yr by 2080. This amount represents a small increase (1.5%) relative to the global CH4 emissions of 553 Tg/yr that have been estimated based on atmospheric inversions.
In other words, even if the poorly understood long-term processes aren’t sustained, the short term methane/temperature relationship itself doesn’t lead to climate catastrophe.
The favorite thoroughbreds of the methane scare are proving to be little more than a bunch of claimers.
Sweeney, C., et al., 2016. No significant increase in long-term CH4 emissions on North Slope of Alaska despite significant increase in air temperature. Geophysical Research Letters, doi: 10.1002/GRL.54541.