October 8, 2009

The Ups and Downs of Methane

One of the indisputable facts in the field of global climate change is that the atmospheric build-up of methane (CH4) has been, over the past few decades, occurring much more slowly than all predictions as to its behavior (Figure 1). Since methane is a particularly potent greenhouse gas (thought to have about 25 times the warming power of CO2), emissions scenarios which fail to track methane will struggle to well-replicate the total climate forcing, likely erring on the high side—and feeding too much forcing into climate models leads to too much global warming coming out of them.


Figure 1. Atmospheric methane concentrations, 1985-2008, with the IPCC methane projections overlaid (adapted from: Dlugokencky et al., 2009)

Figure 2 shows the year-over-year change in the methane concentration of the atmosphere, and indicates not only that the growth rate of methane has been declining, but also that on several occasions during the past decade or so, it has dropped to very near zero (or even below) indicating that no increase in the atmospheric methane concentration (or a even a slight decline) occurred from one year to the next.


Figure 2. Year-to-year change in atmospheric methane concentrations, 1985-2008, (source: Dlugokencky et al., 2009)

This behavior is quite perplexing. And while we are not sure what processes are behind it, we do know one thing for certain—the slow growth of methane concentrations is an extremely cold bucket of water dumped on the overheated claims that global warming is leading to a thawing of the Arctic permafrost and the release of untold mega-quantities of methane (which, of course, will lead to more warming, more thawing, more methane, etc., and, of course, to runaway catastrophe).

To some, the blip upwards in methane growth in 2007 (Figure 2) was a sure sign that the methane beast was awakening from its unexpected slumber. Climate disaster was just around the corner (just ask Joe Romm).

But alas, despite the hue and cry, in 2008 the increase in methane, instead of equaling or exceeding the 2007 rise, turned out to be only about half of the 2007 rise. And together with information on from where it seemed to emanate (the tropics rather than the Arctic), it cannot be taken as a sign that the slow methane growth rate during the past decade was coming to an end as a result of an Arctic meltdown.

Here is how NOAA methane-guru Ed Dlugokencky and colleagues put it in their publication last week describing recent methane behavior:

We emphasize that, although changing climate has the potential to dramatically increase CH4 emissions from huge stores of carbon in permafrost and from Arctic hydrates, our observations are not consistent with sustained changes there yet.

The factual portion of their conclusion remains the same, with or without the inclusion of the final word (but it sure was nice of them to throw it in there as a bone to climate catastrophists the world over).

Reference

Dlugokencky, E. J., et al., 2009. Observational constraints on recent increases in the atmospheric CH4 burden. Geophysical Research Letters, 36, L18803, doi:10.1029/2009GL039780.




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