Methane fluxes in the high northern latitudes for 2005–2013 estimated using a Bayesian atmospheric inversion

Abstract

<p><strong>Abstract.</strong> We present methane (CH<sub>4</sub>) flux estimates for 2005 to 2013 from a Bayesian inversion focusing on the high northern latitudes (north of 50° N). Our inversion is based on atmospheric transport modelled by the Lagrangian particle dispersion model, FLEXPART, and CH<sub>4</sub> observations from 17 in-situ and 5 discrete flask-sampling sites distributed over northern North America and Eurasia. CH<sub>4</sub> fluxes are determined at monthly temporal resolution and on a variable grid with maximum resolution of 1° × 1°. Our inversion finds a CH<sub>4</sub> source from the high northern latitudes of 82 to 84 Tg y<sup>−1</sup>, constituting ~15 % of the global total, compared to 64 to 68 Tg y<sup>−1</sup> (~12 %) in the prior estimates. For northern North America, we estimate a mean source of 16.6 to 17.9 Tg y<sup>−1</sup>, which is dominated by fluxes in the Hudson Bay Lowlands (HBL) and western Canada, specifically, the province of Alberta. Our estimate for the HBL, of 2.7 to 3.4 Tg y<sup>−1</sup>, is close to the prior estimate (which includes wetland fluxes from the land surface model, LPX-Bern) and to other independent inversion estimates. However, our estimate for Alberta, of 5.0 to 5.8 Tg y<sup>−1</sup> is significantly higher than the prior (which also includes anthropogenic sources from the EDGAR-4.2FT2010 inventory). Since the fluxes from this region persist throughout the winter, this may signify that the anthropogenic emissions are underestimated. For North Eurasia, we find a mean source of 52.2 to 55.5 Tg y<sup>−1</sup>, with a strong contribution from fluxes in the Western Siberian Lowlands (WSL) for which we estimate a source of 19.3 to 19.9 Tg y<sup>−1</sup>. Over the 9-year inversion period, we find significant year-to-year variations in the fluxes, which in North America and, specifically, in the HBL appear to be driven at least in part by soil temperature, while in the WSL, the variability is more dependent on soil moisture. Moreover, we find significant positive trends in the CH<sub>4</sub> fluxes in North America of 0.38 to 0.57 Tg y<sup>−1</sup> per year, and North Eurasia of 0.76 to 1.09 Tg y<sup>−1</sup> per year. In North America, this could be due to an increase in soil temperature, while in North Eurasia, specifically, Russia, the trend is likely due, at least in part, to an increase in anthropogenic sources.</p>

Methane at Svalbard and over the European Arctic Ocean

“…Monthly correlations range from 0.1 to 0.8 for both the modelled emissions and the Zeppelin Observatory, while for most months standard deviation of the Zeppelin CH4 is below that of the RV Helmer Hanssen, likely reflecting the fact that the latter is exposed to more variable sources as a moving platform at sea level. The agreement between the model and observations is mostly above R 2 =0.3, as Thompson et al (2017) also report for a number of high latitude measurement stations. For some months, the correlation between the model and observations is strikingly high, e.g.…”

“…4A). These regions are responsible for 20% of the world's natural gas and leak rates may be as high as 10% (Hayhoe et al, 2002;Thompson et al, 2017). Furthermore, according to the GAINS-ECLIPSE model, fuel production and distribution represented the largest fraction, ~87%, of CH4 with anthropogenic emissions dominant for the rest of the year (Fig.…”

“…The Arctic region is of great importance since surface temperatures are rising at around 0.4°C per decade, twice as fast as the global average warming rate (Chylek et al, 2009;Cohen et al, 2014), and it contains a number of CH4 sources sensitive to temperature changes. For example, high latitude (>50°N) wetlands are a significant source of Arctic CH4, contributing as much as 15% to the global CH4 budget (Thompson et al, 2017). Furthermore, Dlugokencky et al (2009); Bousquet et al (2011); Rigby et al (2008) link anomalous Arctic temperatures in 2007 with elevated global CH4 mixing ratios in the same year due to increased high latitude wetland emissions.…”

Methane budget estimates in Finland from the CarbonTracker Europe-CH₄ data assimilation system

“…europa.eu/terms_of_use.php) and ECLIPSE (Stohl et al, 2015) provide gridded global anthropogenic emission estimates that have been used for global and regional studies (e.g. Bergamaschi et al, 2005Bergamaschi et al, , 2018Houweling et al, 2014Houweling et al, , 1999Thompson et al, 2017). Although the EDGAR inventory has the advantage of providing a continuously updated emission distribution on a small scale (0.1 Â0.1 ), possible biases between the Northern and Southern Hemispheres and between countries, have been discussed in previous studies (Houweling et al, 2014;Bergamaschi et al, 2015).…”

“…In this study, we examine CH 4 emission estimates in Finland for 2004-2014 using the CarbonTracker Europe-CH 4 (CTE-CH 4 ) data assimilation system (Tsuruta et al, 2017), with an extended observation network in Finland and surrounding regions. Previously, observations from only one site in Finland (Pallas, Finland) have been used for inversion studies (Bergamaschi et al, 2005(Bergamaschi et al, , 2015(Bergamaschi et al, , 2018Bousquet et al, 2011;Monteil et al, 2013;Bruhwiler et al, 2014;Houweling et al, 2014;Thompson et al, 2017), but we improve the analysis in this study by including seven sites. Sensitivity of inversion estimates to the observations is examined by using two different sets of the newly assimilated observations.…”