• Voluntary agreements between industry and government have played a role in the evolution of national policies and have accelerated adoption of best available technology but have not achieved significant emissions reductions.

• Subsidies, support for public research and development, or other incentives to develop and adopt new, low-emitting technologies, when used alone, have higher costs than other approaches; however, these strategies can complement policies targeting emissions directly via market mechanisms and enhance their overall environmental and cost effectiveness (this is particularly important when markets alone fail to achieve needed reductions in emissions; see also Jaffe et al., 2005).

• While information programs alone do not seem to lead to substantial emissions reductions, they can improve the effectiveness of other programs.

• A well-designed mix of policy types can be more effective than a single “pure form.”

The companion report Limiting the Magnitude of Future Climate Change (NRC, 2010c) contains an extensive analysis of the advantages and disadvantages associated with different climate change policy options for reducing U.S. GHG emissions.

At the international level, climate policies have been codified in the UNFCCC and the Kyoto Protocol. Policies for limiting the magnitude of climate change are implemented through a variety of mechanisms such as the Clean Development Mechanism (CDM) and Joint Implementation. While experience with climate change treaties is limited, there is a substantial literature examining other environmental agreements that can provide insights of relevance to climate treaties (e.g., Biermann et al., 2009b; Mitchell, 2003; Young, 2002a,b, 2008, 2009). Drawing on this evidence, the IPCC (Gupta et al., 2007) concludes that there is, as with national-level policy instruments, “high agreement” and “much evidence” to support a number of conclusions about international treaties. The Kyoto Protocol has stimulated national policies and the creation of carbon markets, but its economic impacts are not clear, and its overall ambition with regard to emissions reduction has been limited. There is broad agreement in the literature that, to be successful, a successor agreement to Kyoto will have to be both environmentally effective and cost effective, take account of distributional and equity considerations, and be institutionally feasible (Aldy and Stavins, 2007). These goals are most likely to be achieved if the agreement incorporates goals, specific actions and timetables, rules for participation, and institutional arrangements and provisions for reporting and compliance. Of particular importance are the extent of engagement by national governments and the stringency and timing of the goals (Gupta et al., 2007).