Evaluating methane emissions between 2008 and 2019 in high northern latitudes by using inverse modeling
Authors: Wittig Sophie , Berchet Antoine , Paris Jean-Daniel , Saunois Marielle , Arshinov Mikhail , Machida Toshinobu , Sasakawa Motoki , Worthy Doug , Pison Isabelle 
Published: March 2022

&lt;p&gt;&lt;span&gt;The Arctic is particularly sensitive to global warming and the effects of the increasing temperatures can already be detected in this region by occurring events such as thawing permafrost and decreasing Arctic sea ice area. One of the possible consequences is the risk of enhanced regional greenhouse gas emissions &lt;/span&gt;&lt;span&gt;such &lt;/span&gt;&lt;span&gt;as methane (CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;) due to the exposure of large terrestrial carbon pools or subsea permafrost which have previously been shielded by ice and frozen soil. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Various sources, both natural and anthropogenic, are &lt;/span&gt;&lt;span&gt;presently&lt;/span&gt;&lt;span&gt; emitting methane in the Arctic. Natural sources include wetland&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; and other freshwater biomes, as well as the ocean and biomass burning. Despite the relatively small population in this region, CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; emissions due to human activities are also significant. The m&lt;/span&gt;&lt;span&gt;ain&lt;/span&gt;&lt;span&gt; anthropogenic sources are &lt;/span&gt;&lt;span&gt;the &lt;/span&gt;&lt;span&gt;extraction and distribution of fossil fuels in the Arctic nations and, to a lesser extent, livestock activities and waste management. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;However, assessing the amount of CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; emissions in the Arctic and their contribution to the global budget still remains challenging due to the difficulties in carrying out accurate measurements in such remote areas. Besides, high variations in the spatial distribution of methane sources and a poor understanding of the effects of ongoing changes in carbon decomposition, vegetation and hydrology also complicate the assessment.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Therefore, the aim of this work is to reduce uncertainties on methane emissions in high northern latitudes. In order to achieve that, an inverse &lt;/span&gt;&lt;span&gt;modeling&lt;/span&gt;&lt;span&gt; approach has been implemented by using observational &lt;/span&gt;&lt;span&gt;data sets&lt;/span&gt;&lt;span&gt; of CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; concentrations obtained at 42 surface stations located in different Arctic regions for the period from 2008 to 2019, the atmospheric transport model FLEXPART, as well as available bottom-up estimates of methane emissions provided by process-based surface models and CH&lt;/span&gt;&lt;sub&gt;&lt;span&gt;4&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; emission inventories. The results have been analysed with regards to seasonal and inter-annual fluctuations, spatial differences and trends over the period of study.&lt;/span&gt;&lt;/p&gt;