Both voluntary activities and a variety of policies and measures that lower emissions are currently in place at federal, state, and local levels in the United States, even though there is no comprehensive national climate legislation. Over the remainder of this century, aggressive and sustained greenhouse gas emission reductions by the United States and by other nations would be needed to reduce global emissions to a level consistent with the lower scenario (B1) analyzed in this assessment.

This finding is from chapter 27 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: Evaluation of literature by Coordinating Lead Authors

Description of evidence base: The identification of state, local, regional, federal, and voluntary programs that will have an effect of reducing greenhouse gas emissions is a straightforward accounting of both legislative action and announcements of the implementation of such programs. Some of the programs include the Carbon Disclosure Project (CDP), the American College and University Presidents' Climate Commitment (ACUPCC), U.S. Mayors Climate Protection Agreement,e1e478a5-7364-4177-a575-8ccfc07b9f4a and many other local government initiatives.5648ec0b-1d03-4593-8183-dbd872a1fb79 6f521695-ae62-4da4-8873-f71b604cde69 Several states have also adapted climate policies including California's Global Warming Solutions Act (AB 32) and the Regional Greenhouse Gas Initiative (RGGI). The assertion that they will not lead to a reduction of US CO2 emissions is supported by calculations from the U.S. Energy Information Administration.

New information and remaining uncertainties: The major uncertainty in the calculation about future emissions levels is whether a comprehensive national policy will be implemented.

Assessment of confidence based on evidence: Very High. There is recognition that the implementation of voluntary programs may differ from how they are originally planned, and that institutions can always choose to leave voluntary programs (as is happening with RGGI, noted in the chapter). The statement about the future of U.S. CO2 emissions cannot be taken as a prediction of what will happen – it is a conditional statement based on an assumption of no comprehensive national legislation or regulation.  

References :

• webpage List of Participating Mayors (e1e478a5)
• Symbolic or substantive policy? Measuring the extent of local commitment to climate protection (5648ec0b)
• Harnessing community energy: the keys to climate mitigation policy adoption in US municipalities (6f521695)