It wasn’t that long ago that The Independent reported the detection of unprecedented methane (CH4) emissions from the sea bed of the East Siberian Arctic Shelf by Russian scientists. This has spawned considerable speculation, and concern, about sudden increase of methane concentration in the Arctic due to extreme Arctic warming, which could potentially cause a nasty global-warming feedback since methane is a potent greenhouse gas. That some are very concerned is no surprise.
Some readers at RealClimate have expressed their worry, pointing to recent high levels of Arctic methane concentration based on AIRS (Atmospheric InfraRed Sounder) data. It has even been asked whether there is dramatic increase month-to-month, considering that the AIRS data for March 2012
shows higher values than recorded just one month earlier, in February 2012
Could this be the harbinger of catastrophic Arctic methane release? Is such a thing even possible? In a report at the EGU (European Geophysical Union) conference in 2008, Shakova et al. stated
… we consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time. That may cause ~12-times increase of modern atmospheric methane burden with consequent catastrophic greenhouse warming.
The sudden release of 50 Gt (gigatonnes) of methane in the Arctic would indeed have disastrous consequences, and Shakova et al. are specialists in this field. But what I haven’t yet seen is observational data indicating alarming methane increase in the Arctic recently. Is there such evidence?
I managed to find surface measurements of methane concentration extending at least to the end of the year 2011, for five stations. Three are from stations maintained by the Japan Meteorological Agency, and can be downloaded from the World Data Center for Greenhouse Gases: Minamitorishima, Ryori, and Yonagunijima. The other two are from ESRL (Earth System Research Laboratory), for Barrow and Mauna Loa. Barrow is the furthest north, and is genuinely Arctic. Next most northern is Ryori, then Yonagonijima and Minamitorishima, with Mauna Loa furthest south (but still in the northern hemisphere). Two questions to ask are: 1. Do any of the records show signs of extreme recent rise? 2. Is there indication of more rapid increase in the far north than in more southerly latitudes?
To investigate, I examined the data from 2000 to the present. I removed the seasonal signal (since each record shows a different seasonal pattern of variation) to compute de-seasonalized CH4 concentration. The data then look like this:
All five records show CH4 increase, with the latest rise starting around 2007. But the rates of increase are not “alarming,” and there’s no sign of exaggerated increase after 2007.
As for latitude variation, there’s very little. The five records cover a range of latitudes from 71.3N (Barrow) to 19.5N (Mauna Loa) but they all show very similar time evolution. This is even clearer if we set them all to the same zero point, computing anomalies as the difference between the de-seasonalized values and the average for the period 2000-present:
I don’t see any sign of alarming increase in methane concentration, either in the Arctic or elsewhere, and no sign of greater increase in the Arctic than in other regions.
I do see signs of steady methane increase. Methane is indeed a potent greenhouse gas, and a sudden massive release (50 Gt) would indeed be disastrous. But even steady release at the present rate will raise the level of greenhouse-gas warming, making the global warming problem worse. Surely it’s something to be concerned about, and measures we can take to reduce methane emissions will be beneficial.
And there’s always the possibility of sudden massive release. I honestly don’t know the likelihood of this, but there’s evidence that it has happened in the very-very-distant past, with terrible consequences for life on earth. Therefore I would recommend keeping a very close eye on Arctic (and other!) methane concentration data, because if such an event should come to pass, the sooner we know about it the better our chances of fending off the disaster. I hope it doesn’t happen. If it does, I hope we can cope.