Decreasing anthropogenic methane emissions in Europe and Siberia inferred from continuous carbon dioxide and methane observations at Alert, Canada

The rate of increase in global atmospheric methane (CH 4 ) abundance has steadily declined since the late 1980s with near zero increase from 1999 through 2006. At the Canadian Baseline Observatory at Alert, Canada (82°28′N, 62°30′W), continuous measurements of methane (CH 4 ) and carbon dioxide (CO 2 ) have been made since 1987. During winter, both gases are frequently highly correlated during well‐defined episodes lasting from 2 to 5 days. We observe a gradual decrease in the ratios of CH 4 /CO 2 during these episodes from ∼16 ppb CH 4 (ppm CO 2 ) −1 to ∼12 ppb CH 4 (ppm of CO 2 ) −1 over the entire record. An atmospheric transport model with prescribed CO 2 and CH 4 source distributions is used to partition simulated CH 4 events into contributions by region. We show that anthropogenic emissions from Europe and Siberia account for more than 85% of the CO 2 and CH 4 enhancements simulated at Alert, but without a change in CH 4 emissions, modeled CH 4 /CO 2 ratios remain constant. To reproduce the observed trend in the ratio of CH 4 /CO 2 , the model requires a reduction in emissions of CH 4 on the order of 30 Tg (13.6 to 33.4 Tg) in Europe and Siberia over the observational period. This is about twice the drop reported by the Emission Database for Global Atmospheric Research (EDGAR) emissions inventory and large enough to account for the leveling off of the global atmospheric CH 4 burden observed over the past 20 years.