So says Article 2, section 2, clause 2 of the U.S. Constitution (not that Pres. Obama pays much attention to little details like that...).
So, Senator Jim Webb (D-VA) wrote the president a letter to remind him:
"Dear Mr. President:
I would like to express my concern regarding reports that the Administration may believe it has the unilateral power to commit the government of the United States to certain standards that may be agreed upon at the upcoming United Nations Framework Convention on Climate Change Conference of Parties 15 in Copenhagen, Denmark. The phrase “politically binding” has been used.
Although details have not been made available, recent statements by Special Envoy on Climate Change Todd Stern indicate that negotiators may be intending to commit the United States to a nationwide emission reduction program. As you well know from your time in the Senate, only specific legislation agreed upon in the Congress, or a treaty ratified by the Senate, could actually create such a commitment on behalf of our country.
I would very much appreciate having this matter clarified in advance of the Copenhagen meetings.”
The ill-conceived, "green house gas" Kyoto Protocol was signed by the Clinton Administration back in 1997, but the Senate has never ratified it. As a matter of fact, the U.S. Senate went out of its way not just to say "no", but "h3ll, no!" with the 95-0 passage of the Byrd-Hagel Resolution.
But that was under the leadership of a Republican Congress. Somehow I think the resolve may have dissipated lately.