Estimates of methane emission rates from some Arctic and sub-Arctic areas based on orbital interferometer IASI data

Abstract

Methane is an important greenhouse gas. About half of its sources are directly induced by human activities, and the second half are connected with a variety of natural mechanisms. Many of these mechanisms have a positive temperature dependence. As it is known, the Arctic warming occurs to be approximately two times faster than the rise in global temperatures. This fact draws attention to studying processes of methane emissions in the Arctic, which may cause a positive climate feedback. Particular attention is given to methane emissions from the Arctic seas. For various logistical reasons the concentrations of methane over the Arctic Ocean are not well investigated. In particular, it is true for the cold period of the year. Meanwhile, a spectrometer AIRS and an interferometer IASI retrieve profiles of methane since 2002 and 2007, respectively. These data are publicly available. Both instruments operate in the thermal IR spectrum and record the outgoing radiation of the Earth and the atmosphere. Due to fundamental physical reasons, the content of the gases may be retrieved if a sufficient contrast in the atmospheric temperature takes place. The paper analyzes the data for cases of temperature contrast (the difference between the temperatures at the surface and at a height of 4 km) in excess of 10° C. All the measurements at the altitude range of 0-4 km for the period from 2010 to 2014 were averaged; then the climatological background was deducted from them. It was assumed that the methane anomaly have been proportional to the methane flux. A well-studied area of the West Siberian wetland with the annual emissions of methane 22 Tr was used to calibrate the scale of methane flux. The maps of the spatial distribution of methane emission rates from the sea surface near Norway, Spitsbergen, Novaya Zemlya, the Laptev Sea, and the Sea of Okhotsk, as well as the territory of Alaska were derived. These estimates are confirmed by the existing literature model and field data for Alaska, as well as by estimates of methane emissions derived from measurements of its supersaturation in the surface waters of the East Siberian Arctic Shelf (ESAS) area.