Recent changes in methane mixing ratio and its¹³C content observed in the southwest Pacific region

Abstract

After nearly a decade without growth in atmospheric methane, there are indications of renewed growth from 2007. Reports of this renewal portray it as global in extent, and due wholly or largely to growth in emissions. Surface methane mixing ratios and constituent δ13C values have been measured approximately twice monthly at Baring Head, New Zealand (41°S, 175°E) since 1989. Surface mixing ratios have been measured continuously at Lauder, New Zealand (45°S, 170°E) since 2007. Also at Lauder, tropospheric-mean mole fractions of methane have been retrieved from ground-based near-infrared solar spectra since 2004. These mixing ratio datasets are consistent with growth rates of about 7.5 and 4.9 ppb year−1 during 2007 and 2008. We consider the possible origins of this growth based on their imprint on δ13C values.