Aerosol processes that determine radiative forcing (direct and indirect) must be parameterized by way of process models that describe such phenomena as cloud formation and aerosol and cloud optical properties. Process models emerge from process research. Long-term systematic monitoring of aerosol properties can provide data to test not only process models but also global climate models. Intensive field campaigns provide an opportunity to measure a comprehensive set of chemical and physical parameters that govern features of aerosol forcing.
A method is required for determining both the individual phenomena that most influence climate forcing by aerosols and those that contribute the most uncertainty. As discussed in more detail in Chapter 3, sensitivity analysis (determining the change in model output resulting from change in each input parameter) is the traditional method. Figure 2.1 indicates that sensitivity analysis should ultimately be performed using both global climate and process models, since the magnitude of the sensitivity may depend on the scale of the phenomenon. These sensitivities are then used in principle to define future research directions to narrow the uncertainties associated with specific processes.
Since we are seeking to understand the impact of anthropogenic aerosols on climate, we should explain why we include research in the cleanest