This paper was prepared for the OECD-IEA Climate Change Expert Group (formerly called the Annex I Expert Group) for the purpose of providing useful and timely input on specific topics relevant to international negotiations under the United Nations Framework Convention on Climate Change (UNFCCC). The papers do not represent the views of the OECD, the IEA, or their member countries, rather they are Secretariat information papers intended to help inform countries as well as the UNFCCC audience on key technical issues in the international climate change negotiations.