A23J-02
INSIGHTS INTO THE RECENT RISE IN ATMOSPHERIC METHANE INFERRED FROM OBSERVED MOLE FRACTIONS AND STABLE CARBON ISOTOPES
Tuesday, 15 December 2015: 13:55
3024 (Moscone West)
James W C White1, Sylvia Englund Michel1, Pieter P Tans2, Bruce H Vaughn3, Edward J Dlugokencky4, Owen Sherwood5, John B Miller6 and Kenneth Alan Masarie7, (1)Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, United States, (2)NOAA/Earth System Research Lab, Boulder, CO, United States, (3)University of Colorado, Boulder, CO, United States, (4)NOAA Boulder, Boulder, CO, United States, (5)University of Colorado at Boulder, Institute of Arctic and Alpine Research, Boulder, CO, United States, (6)NOAA Boulder, ESRL, Boulder, CO, United States, (7)NOAA, Boulder, CO, United States
Abstract:
Methane is a troublesome greenhouse gas. It has multiple natural and anthropogenic sources, including microbial production in low oxygen environments, fossil sources related to coal and natural gas production, and biomass burning, making source attribution difficult. Atmospheric methane concentration rose rapidly in the industrial period, increasing by 250%, only to stall out in the first decade this century, and then rising again after 2007. Its emission is strongly related to variables that are hard to predict, such as precipitation rates, biomass burning, and natural gas use, so future projections remain murky. And unlike CO2, which is strongly tied to energy use, anthropogenic impacts on methane are strongly tied to food production. Finally, methane is expected to be released from a thawing Arctic in large, but largely unknown quantities. Understanding methane as a greenhouse gas is imperative if anthropogenic impacts on the climate system are to be managed in the future. This talk addresses what we can say about the recent rise in methane using mole fractions and 13C data from the existing NOAA Cooperative Global Air Sampling Network. The approach is strongly data based, and while we will present model results, the data itself are clear on several points. While attention is increasingly focused on the Arctic, the north-south gradient of CH4 concentration does not support significant changes to Boreal and Arctic emissions. This finding raises the question of how methane will behave in a warmer, wetter world. We use a simple, three end-member model, run in both forward and inverse modes, to look more deeply into the sources of the recent increase. Evidence exists for recent increases in fossil sources, in line with methane production as a fuel source, although the contribution is small. Better data are needed to constrain the 13C of sources, including the fossil sources, a problem we are working on. Importantly, while the current monitoring network is adequate to place bounds on various sources, recent cuts to the network and stalled plans for expansion clearly hamper our ability to quantify the evolution of emissions and sinks of this greenhouse gas, and thus provide as timely and accurate information for policy makers as the problem warrants.
