Below are two ideas that I think may be politically feasible, and can still handle the ultimate problem of very large reductions or mitigations of greenhouse gas emissions.
Number one: Magic! This is also known as the technology solution to climate change. I'm being somewhat facetious here, because technology has solved many of our problems, just as it has also created many of our problems (including this climate change). But expecting technological improvements to come up with a perfect, cheap, and easily-implemented solution to processes that emit vast amounts of carbon dioxide and methane into the atmosphere is something that amounts to playing the technological lottery.
As an example, see the post by Roger Pielke Jr. on open-air capture of carbon dioxide. The assumptions involved in making that concept work are truly heroic. Carbon sequestration from point sources is going to be hard enough, while this concept of open-air capture adds an additional, poorly defined step that must then be combined with the point source sequestration (when the open-air-captured carbon dioxide has to be released from the capturing material, and sequestered using point-source methods).
A historical note: reliance on not-yet-developed technology was the thing that kept Adolf Hitler and the Nazi Party going towards the end of World War II, when it was clear that they were losing. Things did not work out so well for them.
Bottom line is that technology will of course be important, and I wouldn't even rule out some "magical" technology that makes everything easy, but in the meantime we have to look at some solutions that will require actual effort.
Number two: greenhouse gas controls regulated and adjusted through international trading mechanisms. This is very different from the current treaty-based approach that involves unanimous consent by each nation, and treaty ratification in the United States Senate (if it's to be made applicable in the US). Instead, a critical mass of the world economy, which may or may not include the United States, first determines the total level of allowable greenhouse gas emissions for the entire world, then uses whatever method they choose to allocate those omissions to each country, and finally enforces against noncompliance by any country, whether the country likes it or not, through trade duties on exports from the country that exceeds its allocations. Those trade duties could then be used to pay for greenhouse gas mitigations that would balance out the noncompliance by the offending country.
There are two advantages to this approach over a treaty-based approach. First, if enough of the rest of the world is willing to stand up to the United States, and any other country that refuses to participate, they can do so. I think this is crucial because even a Democratic president may not be willing or able to get the United States to agree to significant reductions in greenhouse gas emissions in the next decade or two, especially in light of the two thirds vote of approval necessary for treaty in the United States Senate. Furthermore, just the fact that this possibility exists could make the United States and especially the American business interests more willing to compromise than would otherwise be the case.
The second big advantage in a trade-based approach is that it does not need the two thirds vote requirement in the United States Senate required for a treaty. Trade agreements only need to be approved by a majority of both houses of Congress, something that is much more feasible. Alternatively, the US doesn't sign at all, but that doesn't even matter if the majority of the world's trading economy does sign and enforce the trade agreement. I'm referring to the United States primarily, but other problem countries like Australia and China could also be regulated this way.
I'm not pretending that this approach is easy, as it would have to significantly modify the current World Trade Organization approach to trade, and it would require Europe and Japan to be willing to go to the wall with the United States over trade. I just point out that it's a way to get things done without the entire world being held hostage by one-third of the US Senate. Not easy this way, but the other way is much harder.
I would like the flesh this out at some point, rather just having some barely-described idea, but that will have to wait for a later time.
Enjoy the holidays everybody. I'm off backpacking in Death Valley, and won't be blogging for a week or so.
UPDATE: see the comments - commentators whose opinions I respect suggest that the trade agreements idea is not a feasible method for getting around the legal requirement for a two thirds majority in the Senate. This isn't my field of law, but I still think it would work. See this web site (or click here if you don't have Powerpoint) for more information that trade agreements do not need two thirds majority vote.