Estimation of direct radiative forcing due to non-methane hydrocarbons

The direct radiative forcing due to non-methane hydrocarbons (NMHCs) has not previously been quantified. We use new measurements of infrared absorption cross-sections and a narrow band radiative transfer model to estimate a forcing. An upper limit to the global mean anthropogenic forcing is likely to be in the region of 0.015 W m-2, less than 1% of the forcing due to other greenhouse gases. However, taking account of the natural NMHC loading and the vertical profile of these gases the actual radiative forcing is likely to be somewhat less than this.