Over at the Council of Foreign Relations' site, Michael Levi's got a useful explainer-type thing on the ins and outs of the global climate talks. This part, for instance, is a succinct explanation of what members of Congress want to see from China:
Members of Congress seem to have made the legal form of a Chinese commitment their overarching priority. They want to see China make commitments that are technically legally binding in the same sense that U.S. commitments would be legally binding under an international agreement. And if that's not forthcoming then they would want symmetry. So U.S. commitments would also not be legally binding on the international level.
They seem to be less focused on what the actual content of the commitments is. Some want to see caps that essentially mirror the U.S. approach. There is no way that is going to happen. It doesn't make any sense. It's impractical, but the legal form is more straightforward to understand and really has become a rallying principal not just for people who tend to take a hard line on climate but for a lot of moderates and relatively liberal Democrats.
Meanwhile, there's another lurking worry about any international climate treaty. Don't these things require 67 votes in the Senate before they're ratified by the United States? And seeing as how a cap-and-trade bill may not even get the 60 votes needed to overcome a filibuster, doesn't that mean there's no way in hell the United States is signing on to whatever's hashed out at Copenhagen and beyond? Well, don't rule it out just yet. Levi explains that there are still other options:
Ultimately getting sixty-seven votes for any kind of treaty will be challenging. The administration will probably look at other options. One may be to treat this the same way we treat international trade deals, where you go for passage as a congressional-executive agreement with sixty votes in the Senate and 50 percent in the House. Another may be as an implementing agreement to the UN Framework Convention on Climate Change which has already been ratified by the Senate.
Each of those may impose new constraints on what exactly can be done in an agreement. There are legal and constitutional restrictions on what one can do through a treaty versus a congressional-executive agreement versus an implementing agreement. But they will seek alternative approaches if that's what they think they need in order to get something in place.
Whole thing's worth reading if you need a good primer.