Copenhagen and U.S. Treaty Law

copenhagenAny international agreement reached in Copenhagen can truly be binding on the U.S. only if it is incorporated into domestic law. A treaty is the law of the land, but under Article II of the Constitution, a treaty must be ratified by two-thirds of the Senate. Hard as it is to gain 60 votes in the Senate to pass legislation, it would be even more difficult to secure 67 votes for a treaty. However, there are alternative mechanisms.

The most solid would be an “ex post congressional-executive agreement.” If the President submits a post-Copenhagen agreement to Congress, and it is approved by a simple majority of both the House and the Senate, it has the same force as a treaty. It would still need 60 votes in the Senate to overcome a filibuster, but not 67.

If that method is not politically feasible, a fallback is a sole executive agreement, which would be entered into by the President alone under his independent constitutional powers. Similar variations are treaty executive agreements and ex ante congressional-executive agreements. As a matter of international law, these are just as binding on the U.S. as a treaty. In four different cases, the U.S. Supreme Court has upheld sole executive agreements and their ability to preempt state laws. Most executive agreements are minor, but some have been momentous, such as the 1945 Yalta agreement regarding the post-war world order.

The Constitution gives the foreign affairs power to the President. He is the chief executive and the Commander in Chief. He can also point to other sources of legal authority – the U.S. Senate’s ratification of the United Nations Framework Convention on Climate Change in 1992; the Convention on International Civil Aviation, which would support a sectoral agreement on aviation emissions; several existing congressional authorizations regarding international scientific cooperation; the Endangered Species Act’s authorization of agreements with foreign countries on conservation of listed species; and, conceivably, the Clean Air Act’s authorization of the regulation of greenhouse gases.

The President cannot use executive agreements to do things that are prohibited by existing federal legislation, and Congress could pass a new law nullifying the commitments, though that would have to overcome a presidential veto (unless by then there is a new president with different views). Likely elements of the agreement could only be executed through Congressional legislation, such as an emissions trading program and the appropriation of federal dollars.

U.S. Presidents have entered into more than 1,360 executive agreements since 1982. Most were routine matters that attracted no public attention. In more controversial matters, however, Congress can and sometimes does cut the President off at the knees. Then-Vice President Gore negotiated the Kyoto Protocol in 1997, but the Senate voted 95-0 against any agreement that did not bind developing countries, so President Clinton never submitted Kyoto for ratification. Mindful of that experience, President Obama has been careful not to get too far ahead of Congress; the greenhouse gas reduction goals he announced on November 25 are in line with those already approved by the House and under consideration in the Senate. His ability to bind the U.S. during or after the Copenhagen conference is limited more by politics than by law.

My colleague Hannah Chang has prepared a detailed legal analysis of these issues in a draft working paper that we have posted on our web site, We welcome any comments and reactions.

Michael B. Gerrard is the Andrew Sabin Professor of Professional Practice and the Director of the Center for Climate Change Law at Columbia Law School. He can be reached at