The political accord struck by world leaders at the United Nations negotiations in Copenhagen in December 2009 allows participating countries to express their greenhouse gas commitments in a variety of ways. For example, developed countries promised different percent emissions reductions...

For the foreseeable future, climate change policy will be considerably more stringent in some countries than in others. Indeed, the United Nations Framework Convention on Climate Change explicitly states that developed countries must take meaningful action before any obligations are to be placed...

To succeed in reducing carbon dioxide emissions, a climate policy must establish credible long-term incentives for investments in the new energy-sector capital and in research and development. We argue that credibility implies that international agreements should focus on enhancing coordination...