Decisions made by treaty bodies under some limited circumstances can be “binding” under US law, in the sense of being enforceable without the need for legislation. However, COP decisions under the UNFCCC COP are almost certain to be found not to be binding under US law.
Many international treaties, in addition to directly creating obligations for states parties, also create what are in effect governing or implementing bodies – bodies tasked with implementing obligations, resolving disputes and even, in some cases, proposing new or expanded obligations over time. The primary treaty body created by the UNFCCC is the COP.
The terms of a treaty determine whether any body created by the treaty can make decisions binding on parties to the treaty as a matter of international law. However, the laws of each individual state party to a treaty dictate whether any international law obligation, including an obligation imposed by decision of a treaty body, can be enforced as a domestic law matter without separate legislation.
In the US, for a decision of a treaty body such as the COP to be binding in the sense of being enforceable under US law without further legislation, the decision would have to be clearly within the mandate of the treaty body and the treaty would have to be considered “self-executing” under US law. Most treaties that regulate economic matters, and decisions made by bodies created by those treaties are not considered self-executing.
Leaving aside the question of the scope of the mandate of the COP under the UNFCCC to impose obligations that are internationally binding on Parties, it is clear as a matter of US law that such decisions, whether or not binding, would not be considered self-executing, and therefore could not be enforced without separate legislative authority. At the time of the ratification of the UNFCCC in 1992, both the Legislature and the Executive agreed that, in adhering to the Treaty, the US was not agreeing to be legally bound by COP decisions. Recently, US courts – including the Supreme Court in the 2008 case of Medellin v. Texas – have declared that decisions made by COP-like bodies are not self-executing and therefore do not override inconsistent domestic law absent separate legislative action.
Although COP decisions are not binding in US law, the US Executive could choose to comply with COP decisions to the extent it has authority under existing environmental statutes. However the scope of executive authority under these statutes is limited, and its exercise is subject to judicial challenge. Environmental Protection Agency (EPA) actions regulating greenhouse gases (GHGs) are already subject to numerous pending lawsuits brought by industrial interests and certain states. Financial commitments require legislation.