Perturbed Earth: Why is Heat-Trapping Methane on the Rise?

Globally, atmospheric methane levels have been on the rise over recent years. And though the rate of rise is not as dramatic as seen during the late 1980s (yet), the relative rise of atmospheric methane has caused concern among scientists.

Methane is a major heat trapping gas. And it is the #2 driver of human-forced global warming behind fossil fuel burning based CO2 according to NOAA’s Earth Systems Research Lab. It also has an out-sized potential to swing global heat trapping values higher due to the fact that a single molecule of methane can trap around 86 times more heat than a single molecule of CO2 over the same period of time.

ch4_trend_all_gl

(Global trends in methane show a concerning jump in atmospheric values since leveling off in the mid-2000s. A combination of earth environment feedbacks to warming and fossil fuel related extraction, burning and transport activity are primary suspects for this increase. Image source: NOAA ESRL.)

Methane is a much shorter lived gas (one molecule lasts 8 years in the atmosphere while a molecule of CO2 lasts 500 years), and atmospheric concentrations of methane are far, far lower than CO2 (measured in parts per billion, not parts per million), however. Which is one of the reasons why CO2 (primarily from fossil fuel based burning) is the gas in the driver’s seat of the majority of present warming.

Given this context, the new upward swing in methane is troubling for a number of reasons. Which begs the question — where is the excess methane coming from?

One primary suspect is that the Earth System, warmed by fossil fuel burning, is starting to produce its own feedback carbon emissions. The way this works is that warmer wetlands (a major source of methane) become more biologically active and, in turn, produce more methane. Heavier rains might provide more flooded regions in which microbes become productive. And thawing permafrost in the far north may be providing new wetland based methane sources. So the nascent methane emissions could be coming from such varied sources as tropical wetlands (as some experts point out), from thawing and expanding biologically active permafrost zones, from increasing wildfire activity, from increasing methane emissions due to drought, or any combination of the above.

Add in potentially very leaky and large-scale, fossil fuel infrastructure related to gas and legacy infrastructure related to coal and the list of suspects grows very long indeed. A hint at where the larger sources of methane show up, at least at present, is provided by the atmospheric observatories. In particular, I’m going to turn to the Copernicus Atmospheric Monitoring System (CAMS) for this part of today’s discussion:

Atmospheric Methane Hot spots

(Global atmospheric methane hot spots indicated by CAMS.)

What we find from looking at this map is that the highest concentrations of methane presently correspond with the densest collections of fossil fuel based industrial activity. This jibes with findings that 60 percent of the presently elevated atmospheric methane value is due to human activity — leaky gas infrastructure, leaky coal mines, and various human-based farming practices that produce methane (rice farming, cow belches etc). It also highlights the recently discovered fact that fossil fuel based leaks are 60 percent more extensive than previously indicated. Confusing this point is the recent Nature finding that though leaky gas and coal infrastructure were more leaky than expected, the large fossil fuel based infrastructure methane emission was not increasing over time.

So the visible, top-down readings in the CAMS monitor may mask a larger feedback delta, or change, in how the the Earth System itself is producing methane. In other words, the new bump in methane may be coming from a perturbed Earth.

As noted by NOAA research scientist Lori Bruhwiler in a recent Wired article:

“The most important science question we face now is the question of carbon-climate feedbacks. The question that’s really important is, what’s coming down the road?”

In other words, is the recent methane spike coming from changes to the Earth System driven by the longer term fossil fuel based warming? And if so, how much will it continue to feed back? How much more methane can we expect from tropical wetlands, fires, droughts and thawing permafrost? This is a big question with wide-ranging implications for our climate future.

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