Geophys. Res. Lett. doi:10.1029/2009GL039780 (2009)

The atmospheric concentration of methane — a potent greenhouse gas — has been climbing over the past two years after remaining flat for nearly a decade. This shift has prompted concern that frozen carbon deposits in the Arctic are starting to melt, which could greatly accelerate climate change.

But Ed Dlugokencky of the National Oceanic and Atmospheric Administration and James White of the University of Colorado, both in Boulder, and their colleagues report that sustained melting of these frozen stores has yet to begin. Their analysis of air samples from around the world indicates that in 2007 the extra methane emissions came from northern wetlands, and that in 2008 they came from tropical wetlands.