The 1992 U.N. Framework Convention on Climate Change requires that signatories, including the United States, establish policies for constraining future emission levels of greenhouse gases, including carbon dioxide (CO2). The George H.W. Bush, Clinton, and George W. Bush Administrations each drafted action plans in response to requirements of the convention. These plans have raised significant controversy and debate. This debate intensified following the 1997 Kyoto Agreement, which, had it been ratified by the United States, would have committed the United States to reduce greenhouse gases by 7% over a five-year period (2008-2012) from specified baseline years. Controversy is inherent, in part, because of uncertainties about the likelihood and magnitude of possible future climate change, the consequences for human wellbeing, and the costs and benefits of minimizing or adapting to possible climate change. Controversy also is driven by differences in how competing policy communities view the assumptions underlying approaches to this complex issue. This paper examines three starting points from which a U.S. response to the convention is being framed. These starting points, or policy "lenses," lead to divergent perceptions of the issue with respect to uncertainty, cost and benefit accounting, and urgency. They also imply differing but overlapping processes and actions for possible implementation, thus shaping recommendations of policy advocates concerning the federal government's role in reducing greenhouse gases. A technological lens views environmental problems as the result of inappropriate or misused technologies. The solutions to the problems lie in improving or correcting technology. The implied governmental role would be to provide leadership and incentives for technological development. An economic lens views environmental problems as the result of inappropriate or misleading market signals (prices). The solutions to the problems lie in ensuring that the prices of goods and services reflect their total costs, including environmental damages. The implied governmental role would be to improve the functions of the market to include environmental costs, so the private sector can respond efficiently. An ecological lens views environmental problems as the result of indifference to or disregard for the planet's ecosystem on which all life depends. The solutions to the problems lie in developing an understanding of and a respect for that ecosystem, and providing people with mechanisms to express that understanding in their daily choices. The implied governmental role would be to support ecologically based education and values, as well as to promote "green" products and processes, for example through procurement policies and labeling requirements. Some initiatives are underway; all the perspectives are relevant in evaluating them and possible further policies. The purpose here is not to suggest that one lens is "better" than another, but rather to articulate the implications of the differing perspectives in order to clarify terms of debate among diverse policy communities.