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Atmospheric methane evolution the last 40 years
Title: Atmospheric methane evolution the last 40 years
Authors: Dalsøren, Stig B.Myhre, Cathrine LundMyhre, GunnarGómez Peláez, Ángel Jesús ORCID RESEARCHERID SCOPUSID Autor AEMETSøvde, Ole A.Isaksen, Ivar Sigmund AngellWeiss, Ray F.Harth, Christina M.
Keywords: Atmospheric methane; Emissions; Metano; Química atmosférica; Transporte de contaminantes
Issue Date: 2016
Publisher: European Geosciences Union
Citation: Atmospheric Chemistry and Physics. 2016, 16(5), p. 3099-3126
Publisher version:
Abstract: Observations at surface sites show an increase in global mean surface methane (CH4) of about 180 parts per billion (ppb) (above 10 %) over the period 1984–2012. Over this period there are large fluctuations in the annual growth rate. In this work, we investigate the atmospheric CH4 evolution over the period 1970–2012 with the Oslo CTM3 global chemical transport model (CTM) in a bottom-up approach. We thoroughly assess data from surface measurement sites in international networks and select a subset suited for comparisons with the output from the CTM. We compare model results and observations to understand causes for both long-term trends and short-term variations. Employing Oslo CTM3 we are able to reproduce the seasonal and year-to-year variations and shifts between years with consecutive growth and stagnation, both at global and regional scales. The overall CH4 trend over the period is reproduced, but for some periods the model fails to reproduce the strength of the growth. The model overestimates the observed growth after 2006 in all regions. This seems to be explained by an overly strong increase in anthropogenic emissions in Asia, having global impact. Our findings confirm other studies questioning the timing or strength of the emission changes in Asia in the EDGAR v4.2 emission inventory over recent decades. The evolution of CH4 is not only controlled by changes in sources, but also by changes in the chemical loss in the atmosphere and soil uptake. The atmospheric CH4 lifetime is an indicator of the CH4 loss. In our simulations, the atmospheric CH4 lifetime decreases by more than 8 % from 1970 to 2012, a significant reduction of the residence time of this important greenhouse gas. Changes in CO and NOx emissions, specific humidity, and ozone column drive most of this, and we provide simple prognostic equations for the relations between those and the CH4 lifetime. The reduced lifetime results in substantial growth in the chemical CH4 loss (relative to its burden) and dampens the CH4 growth.
Sponsorship : This work was funded by the Norwegian Research Council project GAME (Causes and effects of Global and Arctic changes in the Methane budget), grant no. 207587, under the program NORKLIMA, and the EU project ACCESS (Arctic Climate Change Economy and Society). ACCESS received funding from the European Union under grant agreement no. 265863 within the Ocean of Tomorrow call of the European Commission Seventh Framework Programme.
ISSN: 1680-7316
Appears in Collections:Artículos científicos 2015-2018

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