Global Warming Alert: Methane Levels Continue to Climb
by Bill Chameides | May 8th, 2014
posted by Erica Rowell (Editor)
Wetlands are the largest natural source of atmospheric methane, and methane emissions from wetlands are sensitive to temperature. This means that as temperatures rise, more methane is emitted, causing more warming. A positive feedback that could spell trouble for the climate. (Kelly Fike/USFWS)
Troubles from wetlands’ bubbles?
It was way back in 2008 — one of the very first posts of TheGreenGrok — when we reported that atmospheric concentrations of methane in 2007 were no longer stable. It was a troubling finding.
For one, methane is a potent greenhouse gas, some 25 times more effective as a global warmer than carbon dioxide. And methane concentrations had already risen significantly — growing by more than a factor of two since the 1800s, from about 720 parts per billion to more than 1,720 parts per billion by 1990. Much of that increase could be attributed to human activities: coal mining, rice cultivation, ranching.
But suddenly in the late 1990s things on the methane front changed — and for the better. For reasons we did not entirely understand [pdf] methane concentrations stabilized at about 1,780 parts per billion. High-fives all around among climate scientists — it seemed like we might have dodged at least one climate bullet.
But then came a 2008 report from the National Oceanic and Atmospheric Administration (NOAA): measurements made in 2007 indicated that, for the first time in nearly a decade, methane concentrations had inched upward. It was a small increase (0.5 percent) but still significant. (See also here.)
But it was only one year of data and perhaps, as I suggested in that 2008 post, “just a 1-year blip.”
Data Now in: No Blip
Recently, NOAA’s Earth System Research Laboratory released its Annual Greenhouse Gas Index, “a measure of the warming influence of long-lived trace gases and how that influence is changing each year.” The data presented on methane is striking and unequivocal (see below).
The atmospheric concentration of methane has increased in each year since 2007. In 2009, methane concentrations broke the 1,800 parts-per-billion mark and are now above 1,820 parts per billion.
What’s the Story? Why the Increase?
The short answer — we don’t really know. We didn’t have a good understanding of why methane stabilized in the late 1990s and early aughts, and we’re not much better off now. We’ve got lots of hypotheses, ranging from gas leaks to cow burps. And some strange things seem to be occurring over the Arctic Ocean of late.
But it’s the possibility that the rise is coming from natural sources responding to rising temperatures — a climate feedback — that is most worrisome.
For example, consider methane emissions from wetlands, the largest natural source of atmospheric methane. Because it is a “natural” source, one might be inclined to conclude that it should not be a concern if we’re worried about human caused climate change. That conclusion would be wrong.
As confirmed in a recent paper in the journal Global Change Biology by Merritt Turetsky of the University of Guelph, Canada, and colleagues, emissions of methane from wetlands are temperature-sensitive. (Water level and vegetation among many others are also important factors.) As temperatures rise, generally speaking, so do methane emissions.* Because methane is a greenhouse gas, this can set up a so-called positive feedback loop:
» Increasing temperatures lead to more methane emissions.
» More methane emissions lead to higher methane concentrations.
» Higher methane concentrations lead to more warming and higher temperatures.
» Higher temperatures lead to more methane emissions.
» And so it goes…
Methane bubbles being generated from a heated bog. Has the makings of a witches’ brew.
* The response to temperature and strength of methane emissions from wetlands varies regionally (northern latitude wetlands are more sensitive to temperature increases) and by wetland type (bogs and swamps are more sensitive to temperature than fens).
Post updated 5/8/2014.
Added a link providing a better source for the statement that methane is roughly 25 times more effective a warmer than carbon dioxide.
and: positive feedback, wetlands