The level of 1990 greenhouse gas emissions can be significantly reduced at relatively low cost, says Thomas Lee, Massachusetts Institute of Technology. He is the committee chair of the Policy Implications of Greenhouse Warming, Report of the Mitigation Panel. The 500-page report, released June 14 by the National Academy of Sciences, expands the 17-page chapter on mitigation from Implications of Policy Warming, a report of the Synthesis Panel released in April. According to Frank Press, president of NAS, this report will influence people's views and will be important both in the United States and internationally. There are surprises in the report, he says, particularly, that a great deal can be done to lower greenhouse gas emissions at relatively low cost.