New publication: Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing

New, detailed, radiative transfer calculations of greenhouse gas radiative forcing have been performed by Gunnar Myhre (a SMURPHS External Partner at the Centre for International Climate and Environmental Research – Oslo) in collaboration with the University of Reading (a member of the SMURPHS consortium).  They show that the radiative forcing due to methane changes are about 25% higher than would be derived using the empirical expressions adopted by the IPCC, and used widely in studies using simple climate models. Analysis in Etminan et al. (2016) shows that the main reason for the difference with earlier work is the inclusion of methane's absorption bands in the near-infrared, which absorb solar radiation. This enhances the forcing that results from methane's 7.5 micron band, which is the main cause of methane's greenhouse effect. The calculations also showed that at high levels of carbon dioxide, which could start to be experienced later this century, the earlier empirical expressions underestimate the CO2 radiative forcing by about 9%. The paper includes updates to the empirical expressions, which can be used in future studies using simple climate models.

The new study is published in the American Geophysical Union’s journal Geophysical Research Letters.  It is open access and freely available. A general summary and a press release can be found on the Reading website here:

http://www.met.reading.ac.uk/~radiation/grl_methane_summary.pdf

http://www.reading.ac.uk/news-and-events/releases/PR708476.aspx