Lecture, three hours. Requisite: course 203B. Recommended requisite: course 203A. Study of how aerosols can affect weather and climate by interacting with clouds through their potential to act as cloud condensation or ice nuclei and with radiation through their ability to scatter and absorb solar and terrestrial radiation. Origin of large uncertainty estimates attributed to aerosol-cloud and aerosol-radiation interactions in climate change assessments. Structured around reading and discussion of scientific publications. S/U or letter grading.