1. Radiative forcing is the perturbation in the energy balance of the Earth-atmosphere system; the sign convention is that positive and negative values indicate warming and cooling respectively of the troposphere. For comparison the net incoming solar radiation at the top of the atmosphere is 342 W m −2 .
2. Houghton J. T., et al., Eds., Climate Change 1995: The Science of Climate Change (Cambridge Univ. Press, Cambridge, 1995);
3. Climate Change 1994: Radiative Forcing of Climate Change (Cambridge Univ. Press, Cambridge, 1994) [both published for the Intergovernmental Panel on Climate Change (IPCC)].
4. Not included here is radiative forcing due to the effects of anthropogenic aerosols on clouds (so-called indirect radiative forcing). This effect can also lower temperatures at Earth's surface but the magnitude of the indirect effect is extremely uncertain. Some recent model calculations [O. Boucher and U. Lohmann Tellus B 47 281 (1995)] give a range from −0.5 to −1.5 W m −2 for the globally averaged indirect forcing by anthropogenic sulfate aerosol. The IPCC (2) on the other hand gives a range of 0 to −1.5 W m −2 for the indirect forcing by all anthropogenic aerosol.
5. Hao W. M., Liu M.-H., Global Biogeochem. Cycles 8, 495 (1994).