A scary headline for a Saturday morning, and the rest of the story isn’t much better:

ARCTIC emissions of a powerful greenhouse gas jumped 30 per cent in recent years in a worrying hint that global warming might unlock vast stores frozen in permafrost, scientists say.

“It’s too early to call it a trend but if it continues this way there will be serious implications,” said Paul Palmer, a scientist at Edinburgh University in Scotland who was among authors of the study of methane emissions from wetlands.

The 30.6 per cent rise in emissions from the Arctic from 2003-2007, to about 4.2 million tonnes, was the biggest percentage gain for any region of the world’s wetlands in the study in the journal Science with colleagues in Scotland and the Netherlands.

Arctic wetlands account for only two per cent of global emissions from wetlands, most of which are in the tropics. But many experts have pointed to risks that climate change could melt permafrost stores of billions of tonnes of methane, a more potent greenhouse gas than carbon dioxide.

“It’s a warning the scientists have been giving for a while now – what we are seeing are signs of global warming,” Mr Palmer said. (source)

Mr Palmer’s pretty certain – this is “global warming” at work. But even the news story has to concede that only 2% of methane emissions actually originate in Arctic regions, but in any case I thought I’d pay the $15 and download the full paper from Science: Large-Scale Controls of Methanogenesis Inferred from Methane and Gravity Spaceborne Data, and see if the headline and the alarmism was really justified. So I started off with the abstract:

Wetlands are the largest individual source of methane (CH4), but the magnitude and distribution of this source are poorly understood on continental scales. We isolated the wetland and rice paddy contributions to spaceborne CH4 measurements over 2003–2005 using satellite observations of gravity anomalies, a proxy for water-table depth , and surface temperature analyses T_s. We find that tropical and higher-latitude CH4 variations are largely described by and T_s variations, respectively. Our work suggests that tropical wetlands contribute 52 to 58% of global emissions, with the remainder coming from the extra-tropics, 2% of which is from Arctic latitudes. We estimate a 7% rise in wetland CH4 emissions over 2003–2007, due to warming of mid-latitude and Arctic wetland regions, which we find is consistent with recent changes in atmospheric CH4.

The paper uses a model to estimate the global distribution of methane emissions according to changes in temperature and water-table depth. The temperature data originates from the NCEP/NCAR database. The total emissions of methane from global wetlands is claimed as 227 Tg/year (1 Tg = 1 million metric tonnes), from the IPCC AR4 report.

By analysing the temperature and water table distribution, the paper claims that arctic emissions have increased by 30.6% from 2003 – 2007. Since total emissions from the Arctic is only about 4.2 Tg/year in 2007 (about 2%), this means that in the period covered by the paper, those emissions have risen by about 1 Tg/year, which is less than 0.5% of total methane emissions. So whilst it is correct that the increase is 30%, this arises from the fact that it is calculated by reference to a tiny number as a percentage of a slightly tinier number.

To put this into perspective, here is the graphic from the paper showing the changes in emissions of methane from different sources between 2003 and 2007:

Changes in methane emissions plotted against year

It is obvious that the areas where methane emissions are rising most rapidly are the tropics and the midlatitudes. And although the percentage change in the Arctic is large, the absolute change is very small. I haven’t even bothered to go into the temperature sources – but considering global temperatures as measured by satellite have been pretty steady since about 2001, there would have to be arguments that the contribution arising from the melting of permafrost should be negligible in this period. But I would assume that the NCEP/NCAR figures, since they are based on NOAA data, would show an increase.

The only mention of climate change in the paper is in the very last paragraph:

There is substantial potential for wetland emissions to feed back positively to changes in climate and therefore it is critical that we understand the extent of overlap between wetlands and regions that are most sensitive to projected future warming. We anticipate that the new constraints developed here will ultimately improve model predictions of this feedback.

“Substantial potential” – no evidence, just a hunch. Yet out of that one paragraph, a string of scary news stories has been generated, thanks to an author who has the preset “global warming” bias. The media spin cycle on full blast.