Chapter 8, Key Finding 3

During most of the study period covered by the Second State of the Carbon Cycle Report> (2004 to 2012), inverse model analyses of atmospheric CH4 data show minimal interannual variability in emissions and no robust evidence of trends in either temperate or boreal regions. The absence of a trend in North American CH4 emissions contrasts starkly with global emissions, which show significant growth since 2007. Methane emissions for North America over the period 2004 to 2009 estimated from six inverse models average 66 ± 2 Tg CH4 per year. Over the same period, CH4 emissions reported by the U.S. Environmental Protection Agency equate to a climate impact of 13% of CO2 emissions, given a 100-year time horizon.