This is worrying. Levels of the greenhouse gas methane in the atmosphere seem to be rising having remained stable for nearly 10 years.

Data from the National Oceanographic and Atmospheric Administration (Noaa) in the US suggest concentrations rose by about 0.5% between 2006 and 2007. The rise could reflect melting of permafrost, increased industrialisation in Asia or drying of tropical wetlands.

Concentrations have been more or less stable since about 1999 following years of rapid increases. Industrial reform in the former Soviet bloc, changes to rice farming methods and the capture of methane from landfill sites all contributed to the levelling off.

But the 2007 figure indicates that levels may be on the rise again. This is a worry, because methane is the second most important gas causing man-made climate change. Each molecule causes about 25 times more warming than a molecule of CO2…