Biogeochemistry: Rebalancing the global methane budget.

Abstract

A database of the carbon-isotope 'fingerprints' of methane has been used to constrain the contributions of different sources to the global methane budget. The surprising results have implications for climate prediction. See Letter p.88 Stefan Schwietzke et al. re-evaluate the global methane budget and the contribution of the fossil fuel industry to methane emissions on the basis of long-term global methane and methane carbon isotope records. They find that total fossil fuel methane emissions (fossil fuel industry plus natural geological methane seepage) are not increasing over time, but are 60–110 per cent greater than was previously thought. They also conclude that methane emissions from natural gas, oil and coal production and their usage are 20–60 per cent greater than inventories and that methane emissions from natural gas as a fraction of production have declined from about 8 per cent to 2 per cent over the past three decades.