[en] The National Academy of Sciences' (NAS) report 'Policy Implications of Global Warming' has added weight to congressional debates on the greenhouse effect. The report details the many ways the US can reduce greenhouse gas emissions, and ranks them in terms of cost-effectiveness. The options are also grouped into three categories that take into account implementation obstacles and other costs and benefits. The first category includes energy-efficiency improvements, the second, fossil fuel alternatives and the third, geoengineering fixes. A bill introduced by Cooper and Synor includes many of the options and sets up market-based incentives for reducing emissions - CO₂ credits. The Bush administration is opposing the bill