Variations in global methane sources and sinks during 1910–2010
Open Access
- 9 March 2015
- journal article
- research article
- Published by Copernicus GmbH in Atmospheric Chemistry and Physics
- Vol. 15 (5), 2595-2612
- https://doi.org/10.5194/acp-15-2595-2015
Abstract
Atmospheric methane (CH4) increased from ~900 ppb (parts per billion, or nanomoles per mole of dry air) in 1900 to ~1800 ppb in 2010 at a rate unprecedented in any observational records. However, the contributions of the various methane sources and sinks to the CH4 increase are poorly understood. Here we use initial emissions from bottom-up inventories for anthropogenic sources, emissions from wetlands and rice paddies simulated by a~terrestrial biogeochemical model, and an atmospheric general circulation model (AGCM)-based chemistry-transport model (i.e. ACTM) to simulate atmospheric CH4 concentrations for 1910–2010. The ACTM simulations are compared with the CH4 concentration records reconstructed from Antarctic and Arctic ice cores and firn air samples, and from direct measurements since the 1980s at multiple sites around the globe. The differences between ACTM simulations and observed CH4 concentrations are minimized to optimize the global total emissions using a mass balance calculation. During 1910–2010, the global total CH4 emission doubled from ~290 to ~580 Tg yr−1. Compared to optimized emission, the bottom-up emission data set underestimates the rate of change of global total CH4 emissions by ~30% during the high growth period of 1940–1990, while it overestimates by ~380% during the low growth period of 1990–2010. Further, using the CH4 stable carbon isotopic data (δ13C), we attribute the emission increase during 1940–1990 primarily to enhancement of biomass burning. The total lifetime of CH4 shortened from 9.4 yr during 1910–1919 to 9 yr during 2000–2009 by the combined effect of the increasing abundance of atomic chlorine radicals (Cl) and increases in average air temperature. We show that changes of CH4 loss rate due to increased tropospheric air temperature and CH4 loss due to Cl in the stratosphere are important sources of uncertainty to more accurately estimate the global CH4 budget from δ13C observations.Keywords
This publication has 83 references indexed in Scilit:
- Interpreting methane variations in the past two decades using measurements of CH4 mixing ratio and isotopic compositionAtmospheric Chemistry and Physics, 2011
- Carbon and hydrogen isotopic compositions of stratospheric methane: 1. High‐precision observations from the NASA ER‐2 aircraftJournal of Geophysical Research: Atmospheres, 2003
- Reconstructing atmospheric histories from measurements of air composition in firnJournal of Geophysical Research: Atmospheres, 2002
- Reduced methane emissions from large‐scale changes in water management of China's rice paddies during 1980–2000Geophysical Research Letters, 2002
- On the contribution of anthropogenic Cl to the increase in δ13C of atmospheric methaneGlobal Biogeochemical Cycles, 2002
- Development of analytical methods and measurements of 13C/12C in atmospheric CH4 from the NOAA Climate Monitoring and Diagnostics Laboratory Global Air Sampling NetworkJournal of Geophysical Research: Atmospheres, 2002
- The trend in atmospheric methane δ13C and implications for isotopic constraints on the global methane budgetGlobal Biogeochemical Cycles, 2000
- Simulation of ozone and other chemical species using a Center for Climate System Research/National Institute for Environmental Studies atmospheric GCM with coupled stratospheric chemistryJournal of Geophysical Research: Atmospheres, 1999
- Carbon kinetic isotope effect in the reaction of CH4 with Cl atomsGeophysical Research Letters, 1995
- Differences of the atmospheric CH4 concentration between the Arctic and Antarctic regions in pre‐industrial/pre‐agricultural eraGeophysical Research Letters, 1993