Carbon monoxide plays a primary role in governing OH abundances in the troposphere. It is likely that through this chemical interaction, CO plays an important role in climate forcing by affecting CH4 concentrations. We use a photochemical box model to estimate the indirect global warming potential (GWP) of tropospheric carbon monoxide resulting from its effect on methane abundances. We also consider indirect GWPs of CO due to carbon dioxide production and possible CO GWP ranges due to ozone production to estimate a total CO indirect GWP range over various time horizons. We estimate that for current emission levels, the short-term (<15 years) cumulative radiative forcing due to the direct anthropogenic emission of CO may be larger than the cumulative forcing due to anthropogenically emitted N2O. ¿ 1998 American Geophysical Union