The United States and almost 200 other countries are negotiating under the United Nations Framework Convention on Climate Change (UNFCCC) to address climate change cooperatively beyond the year 2012. Parties agreed to complete the negotiations by the 15th meeting of the Conference of the Parties (COP-15) from December 7-18, 2009, in Copenhagen. However, some nations' leaders have indicated that the Copenhagen outcome is likely to be a political agreement providing a mandate for a later legally binding, comprehensive agreement. The negotiations are intended to decide the next steps toward meeting the objective of the UNFCCC, to stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Most Parties conclude the objective requires avoiding a 2oCelsius increase of global mean temperature from pre-industrial values and reducing global greenhouse gas (GHG) emissions by 50% by 2050 from 1990 levels, with industrialized countries' share to be an 80-95% reduction. The UNFCCC principle of common but differentiated responsibilities among Parties permeates debate about obligations of different forms, levels of effort, and verifiability. Key disagreements remain among Parties: • GHG mitigation: Some countries, including the United States, seek GHG actions by all Parties; many developing ...