Global methane flux into the atmosphere and its seasonal variations

Ground-Level Concentrations of Atmospheric Methane in Southwest Greenland Evaluated Using Open-Path Laser Spectroscopy and Cavity-Enhanced Absorption Spectroscopy

“…Ground-level CH 4 concentrations were determined by OPL in southwestern Greenland for a variety of Arctic landscapes using path lengths ranging from 10 to 280 m and time periods between 0.4 and 37 h. All OPL measurements of ground-level methane concentrations were consistent with the mean value of 1.84 ppmv CH 4 reported by others for Arctic air samples (Dlugokencky et al, 2009;Adushkin and Kudryavtsev, 2010), and with the mean CH 4 concentration reported for July 2012 at Summit Station, Greenland, of 1.86 ppmv (NOAA, 2013). Measurements made with OPL also were in good agreement with independent measurements of samples collected on-site and analyzed using cavity-enhanced laser absorption spectrometry and gas chromatography.…”

“…Despite the extensive data sets of atmospheric CH 4 concentrations collected during eddy covariance studies, relatively few atmospheric CH 4 concentrations from these studies have been published. The atmospheric CH 4 concentration measurements that have been published are from locations far from CH 4 source areas in the Arctic, but are critical for demonstrating a long-term increase in atmospheric CH 4 concentrations globally (Adushkin and Kudryavtsev, 2010;Dlugokencky et al, 2011;Kirschke et al, 2014).…”

“…One molecule of CH 4 is 20 times more effective in terms of radiative forcing than one molecule of carbon dioxide (CO 2 ) (Lashof and Ahuja, 1990). Average global concentrations of atmospheric CH 4 have risen from 0.75 ppm by volume (ppmv) during pre-industrial times to 1.82 ppmv in 2012 (Craig and Chou, 1982;Dlugokencky et al, 2009;Adushkin and Kudryavtsev, 2010;WMO, 2013). Over the next 100 years, CH 4 is expected to contribute 25% of the radiative forcing increase of the atmosphere (IPCC, 2013).…”

Consumption of atmospheric methane in a limestone cave in Indiana, USA

“…Epigenic caves dominate the total land area represented by karst and the CH 4 dynamics of these caves are more representative of the typical biogeochemical conditions present in karst. CH 4 mole fractions in the air of epigenic caves in Gibraltar, Spain, and Australia (Mattey et al, 2013;Fernandez-Cortes et al, 2015;McDonough et al, 2016) are generally below that of the atmospheric background of 1.8 ppm (ppm, parts per million, is used to abbreviate μmol mol -1 , dry air mole fraction) (Dlugokencky et al, 2003;Adushkin and Kudryavtsev, 2010;Dlugokencky et al, 2011). The observations of subatmospheric CH 4 mole fractions in caves and karst have led to suggestions that they are 4 functioning as CH 4 sinks, however questions regarding the processes contributing to low CH 4 mole fractions in caves remain.…”

Kerogen maturation data in the Uinta Basin, Utah, USA, constrain predictions of natural hydrocarbon seepage into the atmosphere

“…The total annual methane budget is estimated to be in the hundreds of teragrams annually, with 600 Tg yr −1 being a consensus value [ Cicerone and Oremland , ; Fung et al ., ; Khalil and Rasmussen , ; Crutzen , ; Stern and Kaufmann , ; Hein et al ., ; Lelieveld et al ., ; White et al ., ; Adushkin and Kudryavtsev , ; Kai et al ., ]. If both sets of estimates are reasonable, then flux due to natural methane seepage is roughly 5% of the total budget.…”