Estimation of direct radiative forcing due to non-methane hydrocarbons

The direct radiative forcing due to non-methane hydrocarbons (NMHCs) has no t previously been quantified. We use new measurements of infrared absorptio n cross-sections and a narrow band radiative transfer model to estimate a f orcing. An upper limit to the global mean anthropogenic forcing is likely t o be in the region of 0.015 W m(-2), less than 1% of the forcing due to oth er greenhouse gases. However, taking account of the natural NMHC loading an d the vertical profile of these gases the actual radiative forcing is likel y to be somewhat less than this. (C) 1999 Elsevier Science Ltd. All rights reserved.