Methane and its global warming potential

This article in the New Scientist entitled 'Methane controls before risky geoengineering, please' by Prof. Kirk Smith, makes the following points:

'Methane is a much more powerful greenhouse gas than CO₂. A tonne of methane is responsible for nearly 100 times more warming over the first five years of its lifetime in the atmosphere than a tonne of CO₂. Methane is removed from the atmosphere much more rapidly than CO₂, with a half-life of 8.5 years compared with many decades for CO₂, but a tonne of methane eventually turns to 2.75 extra tonnes of CO₂ in the atmosphere. Even without taking this into consideration, a tonne of methane emitted today will exert more annual warming than a tonne of CO₂ emitted today until 2075. Not until the year 7300 will the cumulative warming exerted by the two become equal.'

The article criticises the conventional IPCC weighting system that gives a tonne of methane a global warming potential 21 times that of CO₂ over a 100-year period, given the short time scale we face. It points out that this weighting gives equal importance to measures that will reduce warming in 2109 and warming next year.

You can read the article here.