Arctic warming impacts methane sources
Rona L. Thomson, NILU Foto: Ingar Næss
– The Arctic and boreal regions contain globally important areas of wetlands, the dominating natural source of methane, which are sensitive to weather conditions, such as temperature and precipitation. In recent decades, these latitudes have warmed substantially with annual average temperatures in the Arctic increasing at a rate of 0.38°C per decade, explains senior scientist Rona Thompson from NILU (Norwegian Institute for Air research).
– This warming will have important impacts on the Arctic environment, such as the thawing of permafrost, as well as changes to the hydrology and vegetation. It may also have a considerable impact on methane sources, especially those from wetlands, which could act as a positive feedback on global climate.
In a study recently published in the journal Atmospheric Chemistry and Physics, Thompson and her colleagues find evidence that the recent increase in atmospheric methane could be partly due to sources in the high northern latitudes. Thompson and colleagues estimated methane fluxes for 2005 to 2013, based on observations of atmospheric methane from 22 sites distributed over northern Eurasia and North America.
Figure 1: The changing annual northern American and Eurasian methane sources over time (units of Tg CH4 y-1). (Northern America includes Canada and Alaska, and Northern Eurasia includes Europe and Russia, both north of 50°N).
– Our study includes more observations than any earlier studies, and this is also the first time observations from stations in Siberia have been included in a multi-annual study or a study of this scale, explains Thompson. – The study uses a statistical optimization method in which observations of atmospheric methane concentrations are used, with the help of a model of atmospheric transport, to improve knowledge about methane fluxes.
Large emissions in Canada
One of the key findings was that emissions of methane in Alberta, Canada, are much larger than previously thought and are likely to be coming from the oil and gas industries, an important human source of methane. Methane inevitably leaks from oil and gas wells, as well as from storage and transport facilities, to the atmosphere.
– It is perhaps not very surprising that we find such high methane emissions there, says Thompson.
– Alberta produces 72% of Canada’s natural gas and has Canada’s largest shale gas reserves. In addition, there are large tar sand operations in Alberta, which are also sources of methane. It was, however, surprising that the emissions are very much underestimated in published inventories.
Are Arctic emissions increasing?
Figure 2: Annual averaged methane emissions to the atmosphere (units of gCH4 m-2 day-1) estimated in this study.
Moreover, Thompson and her colleagues found that the source of methane to the atmosphere increased in northern North America and Eurasia over the period of the study. The question though is why. Although Thompson and colleagues cannot fully answer this question yet, there are indications that it could be due to an increased production of methane in Arctic and sub-Arctic wetlands. Rising temperatures in the Arctic may enhance the microbial processes producing methane in wetlands. However, other changes, such as to the hydrology and vegetation, may over longer time periods counter the temperature effect. This is a big uncertainty in the climate feedback effect of Arctic methane.
– Our study only covers one decade, and that is not very long. We need to do more research and follow the emissions for longer before we can make any conclusions about long-term changes in the Artic methane source, Thompson concludes.
Thompson et al.: Methane fluxes in the high northern latitudes for 2005–2013 estimated using a Bayesian atmospheric inversion, Atmospheric Chemistry and Physics, 17, 1–20, doi:10.5194/acp-17-3553