I posted a few weeks ago about the breakthrough that (seemingly) explains the sharp rise in atmospheric methane we’ve measured since late 2006. For those who haven’t been following along, the most recent graph of atmospheric methane I posted was just a little over a month ago:

The mystery was, of course, where the heck all that extra methane was coming from.

The big fear, for at least some of us, was that it was the leading edge of the shock wave from the methane bomb going off. There’s something like 1.6 trillion tons of carbon (not CO2 or methane) in the Arctic region in the form of permafrost, so if even a very small portion of that thawed and was turned by microbes into CO2 and methane, or a big enough burp from Arctic methane hydrates was released, we would be in an almost unimaginable amount of trouble.

Then came the story I alluded to above, which I wrote about on September 28th (Methane mystery solved?), about an NOAA study that was summarized in an NOAA press release by saying:

Unusually high temperatures in the Arctic and heavy rains in the tropics likely drove a global increase in atmospheric methane in 2007 and 2008 after a decade of near-zero growth, according to a new study. Methane is the second most abundant greenhouse gas after carbon dioxide, albeit a distant second.

…

“At least three factors likely contributed to the methane increase,” said Ed Dlugokencky, a methane expert at NOAA’s Earth System Research Laboratory in Boulder, Colo. “It was very warm in the Arctic, there was some tropical forest burning, and there was increased rain in Indonesia and the Amazon.”

…

Dlugokencky and his colleagues from the United States and Brazil note that while climate change can trigger a process which converts trapped carbon in permafrost to methane, as well as release methane embedded in Arctic hydrates – a compound formed with water - their observations “are not consistent with sustained changes there yet.”

My conclusion was that I was less than comforted by this finding. This was “likely” the cause, and observations are “are not consistent with sustained changes there yet”? That’s a pretty loose conclusion, all things considered.

Now I have to wonder if there’s another cause that hasn’t been connected to the other dots just yet. That big dot is the Three Gorges Dam in China, and the thing that has me thinking such thoughts is the tantalizing item, Chinese dam may be a methane menace:

Marshland created when China’s Three Gorges Reservoir is partially drained during the summer may be a significant source of the powerful greenhouse gas methane, researchers say.

The findings, published in the Journal of Geophysical Research, are among the latest to raise questions over the green credentials of hydropower.

Unfortunately, the article itself is behind a pay firewall, so I can’t say if the findings would account for a sizable portion of the methane increase or something more like 0.001%.

For a refresher on just how large this dam project is, see Wikipedia’s entry, Three Gorges Dam. Notice that the dam started to come online in pieces in 2003, and didn’t get mostly up to speed until 2006/2007. How much of this marshland creation happened in late 2006, when the observed methane levels started to rise?

I don’t know, but I’m going to try to dig up more details on the dam, the amount of methane it’s estimated to have produced, etc.

As for what this means if the dam is a major contributor to this run-up, I think it’s a mixed bag. It strengthens the conclusion from NOAA that it wasn’t the permafrost or hydrate bombs going off, but it also points to our being locked into those emissions, unless someone has a suggestion about how we can convince China to radically alter how they use their immense and very expensive electron pusher.

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