若從美國歷年相關立法來看，其潔淨空氣法（CAA）在Massachusetts v. EPA訴訟案後雖已納入溫室氣體管制，但因溫室氣體的影響層面過於廣泛，並不適合規範作為管制溫室氣體的主要規範，而美國總統歐巴馬在2008年上任後宣布將制訂新的能源與氣候政策作為其任內最優先執行的政策，為回應其綠色新政，眾議院及參議院分別在2009年提出新的氣候法案-美國潔淨能源與安全法（ACES）與潔淨能源工作與美國電力法（CEJAPA），兩法規範即使略有差異，皆不脫離氣候變遷調適措施與潔淨能源科技發展等架構，配合再生能源使用標準（RPS）與再生燃油標準（RFS）的實施，將可協助美國有效達成減量目標。
Recently the Kyoto Protocol would be expired at the end of 2012, in order to reach a new agreement of global emission reduction, the post-Kyoto negotiations under UNFCCC have been held since 2007. The major issues include reduction targets after 2012, adaptation fund, carbon trade and technology transfer. The 2009 conference was held in Copenhagen, Denmark. After the conference, delegates approved the Copenhagen Accord, which was discussed by U.S. and other four developing countries, is not legally binding. Even so, the America played an important role in the negoitation process, and most countries around the world usually pay attention to U.S. movements during the post-Kyoto negotiation period.
For the past years, the U.S. Clean Air Act（CAA）regulate greenhouse gas after Massachusetts v. EPA, however, the CAA is not appropriate to regulate greenhouse gas because the influence of greenhouse gas emission is extensive. In 2008, the U.S. President Obama announced that he would set a new energy and climate policy as a top priority during his presidential terms. To respond to Obama’s green policy announcement, the House of Representitives and Senate set two climate laws, American Clean Energy and Security Act（ACES）and Clean Energy Jobs and American Power Act（CEJAPA）in 2009. Although these two laws have many different regulations, they both have a framework about climate mitigation, adaptation and clean energy technology development. If the U.S. government operate the framework with renewable portfolio standards（RPS）and renewable fuel standards（RFS）, they would reach their redution target effectively.
Focusing on the interation between UNFCCC and U.S., the dispute of UNFCCC could not be settled and the U.S. position on climate change would lead to some conflict between developed and developing countries. To reach an agreement among both side, U.S. must use bilateral or multilateral negotiation ways to mitigate the conflict between developed and developing countries. Besides, the UNFCCC agreement in post-Kyoto period may have some influnces on U.S. new climate law. If the U.S. can promote the advantages of their new climate law and stand their climate position to effect the result of the post-Kyoto negotiation, the U.S. new climate laws may be carry out more smoothly.