Aerosols play key roles in many aspects of Earth’s climate: (1) they interact directly with the incoming radiation, (2) they alter the cloudiness and thus alter the radiation balance, and (3) they alter the chemical composition that further influences the radiation field.  Each of these roles is not well quantified and thus the role of aerosols in the atmosphere is one of the largest uncertainties in the climate system, especially as it relates to human induced changes.

I will briefly discuss the phenomenology of these roles played by aerosols.  I will briefly discuss some of the issues related to the difficulty in calculating the role of aerosols.  I will exemplify some of the issues by using results from our laboratory.