Ron Smith continues his Yale course on the atmosphere, ocean, and environmental change with a lecture on global warming projections. After a review of exam material, he walks through the IPCC's greenhouse gas emissions scenarios, comparing outcomes ranging from about 450 to 800 parts per million of carbon dioxide by 2100 and the associated warming estimates of roughly 2 to 4 degrees Celsius. He then works through the problems such warming could cause, considers a few possible advantages, and closes with a survey of actions that might reduce future warming, from emissions cuts to broader policy responses. The lecture is data driven and blackboard style, typical of the Open Yale Courses recordings, and assumes the physical groundwork laid in earlier sessions on atmospheric composition and radiative forcing.