The absence of US national action oil global climate change policy has prompted initiatives by the US Congress, cities, states, and regions toward what is likely to become it long-term, collaborative effort to harmonize national energy and climate policies. This upward evolution in the face of it reluctant administration is historically consistent with the development of national legislation on other environmental and social issues in the US. At the heart of this movement is the need to resolve conflicts between high-intensity use of low-cost fossil energy Supplies, and the dominating impact of carbon dioxide emissions oil global climate change. US states are among the largest carbon dioxide emitters in the world and play a critical role in supplying and transforming energy, its well as consuming it, for economic advantage. State governments are also likely to have to shoulder some of the cost of potentially extensive climate damages and bear the brunt of the cost of implementing future federal mandates. As a result, many are taking proactive stances oil the development of climate mitigation policy to prepare for, accelerate, and/or guide national policy. As US states show leadership on addressing greenhouse gas emissions, they also play an important role in forging policies and measures that reduce economic conflict between energy and climate goals. A number have launched or completed greenhouse gas mitigation plans and other major policies in the past few years that address these conflicts through: (1) finding ways to reduce mitigation costs, including the use of incentive-based policy instruments; (2) promoting ail open and democratic policy process that includes major stakeholders; (3) promoting equity across socioeconomic groups, regions, and generations; and (4) promoting interregional cooperation. The results are promising and suggest that the state arena for climate and energy policy is evolving quickly and constructively toward alternatives that reduce conflict. Regional efforts are also unfolding, along with greater congressional attention to the lessons learned and commitments made by sub-federal actions. In the next few years many national energy and climate conflicts are likely to be tested and addressed by states. Among these, Pennsylvania is likely to be an important player due to its high profile of energy production and potential for leadership. (c) 2005 Elsevier Ltd. All rights reserved.