Arctic Methane Trends

Characterization and improved process understanding of Arctic trace gases (particularly methane and ozone) has been identified as an important focal area; a Trace Gases Working Group to address this area is currently being organized.  Globally, CO2 and CH4 are responsible for ~82% of increased direct radiative forcing since 1750 by long-lived greenhouse gases.  Increased radiative forcing by CO2 has been measured at two Northern Hemisphere sites and found to be consistent with radiative transfer models.  Natural emissions of these gases are of particular interest in the Arctic where there are large vulnerable reservoirs of carbon in soil and possibly clathrates that can be released to the atmosphere as CO2 and CH4 by thawing and decomposition, potentially acting as a positive feedback on global climate. Atmospheric CH4, CO2, and their stable isotopic composition are measured at seven of the IASOA observatories (Alert, Ny-Ålesund, Summit, Tiksi, Barrow, Cherskii, and Pallas). After a hiatus in growth of its atmospheric burden from 1999-2006, CH4 began increasing in 2007. Renewed growth in globally averaged CH4 since 2007 is attributed to a combination of increased tropical natural emissions and emissions from fossil fuel production, agriculture and waste. The increase in annual mean from 2013 to 2014 for CH4 zonally averaged over 53-90°N was 11.9±2.0 ppb which is comparable to the global CH4 increase (9.4±1.4 ppb). Although inter-annual variability in Arctic emissions are captured in the Arctic observations, large sustained increases in Arctic CH4 emissions have not been observed.