A wide range of renewable electricity policies has been adopted at the state level in the United States, but to date there has been no large-scale, empirical assessment of the effect of these policies on carbon emissions. Such an assessment is important because scholars have pointed out that increases in renewable electricity will not necessarily lead to declines in carbon emissions. We examine the effects of a range of policies across 39 states. We find significant and robust decreases in carbon emissions associated with the introduction of public benefit funds, a form of "carbon tax" adopted by 19 states to date. Our aim in this paper is not to provide a final judgment on these policies, many of which may not have been in place long enough to show strong effects, but to shift the attention of the research community away from proximate measures such as increases in clean electricity generation and onto measurement of lower carbon emissions. (C) 2012 Elsevier Ltd. All rights reserved.