An influential climatologist who used the results of complex scientific models he developed to become a leader in pressing for action to address global warming, Stephen Henry Schneider was born in New York City in 1945 and grew up on Long Island, where he made a telescope at age 13 and was thrilled to see the rings of Saturn. At Columbia University, he earned an undergraduate degree in mechanical engineering in 1966, and a Ph.D. in mechanical engineering and plasma physics in 1971. Dr. Schneider was elected to serve on a new student-faculty senate that was established at Columbia after a wave of student demonstrations in 1968. He told the National Academy of Sciences that this experience taught him to strive to see both sides of every question. Dr. Schneider began postdoctoral study at the Goddard Institute for Space Studies of NASA, then moved to the National Center for Atmospheric Research in Boulder, Colo. In 1992 he joined the Stanford faculty, where he held several positions. That year he was awarded a MacArthur fellowship, in part for his contributions in communicating scientific information.