This paper is based on a Master of Science thesis submitted to the MIT Technology and Policy Program in May, 1997, and also appeared as Working Paper 97-003 in the MIT Center for Energy and Environmental Policy Research (CEEPR) series.Includes bibliographical references (p. 29-31).Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/).Supported in part by a grant from Tokyo Electric Power Company to the Joint Program on the Science and Policy of Global Change, and in part by the U.S. Environmental Protection Agency through Cooperative Agreement. no. CR820662-01-0