This Report of the Study of Critical Environmental Problems (SCEP) presents the results of a one-month interdisciplinary examination of the global climatic and ecological effects of man's activities. This Report of the Study of Critical Environmental Problems (SCEP) presents the results of a one-month, interdisciplinary examination of the global climatic and ecological effects of man's activities. The disciplines represented by the fifty full-time participants include meteorology, oceanography, ecology, engineering, economics, social sciences, and law. The Study, which was sponsored by the Massachusetts Institute of Technology, was conducted during the month of July 1970 at Williams College, Williamstown, Massachusetts. The focus was on those environmental problems whose cumulative effects on ecological systems are so large and prevalent that they have worldwide significance. Thus the Study was primarily concerned with the effects of pollution on man through changes in climate, ocean ecology, and large terrestrial ecosystems. Some of the following subjects were investigated by the Work Groups: Climatic Effects: Increasing carbon dioxide content of the atmosphere Particle load of the atmosphere Contamination of the troposphere and stratosphere by subsonic and supersonic aircraft Ecological Effects: DDT and other pesticides Mercury and other toxic heavy metals Oil in the oceans Nutrients in estuaries On these topics several general questions were addressed, such as, What can we say? Where are the gaps in our knowledge? What action programs are needed?