The United States has pledged to sign a treaty to cut greenhouse emissions in half . . . by 2050:
In a statement Tuesday on climate change, President Bush and the other G-8 leaders said they would work with other countries to "consider and adopt" the 50-percent reductions as part of the new United Nations treaty to be negotiated in Copenhagen at the end of 2009. The leaders made it clear in their statement that they expected developing countries such as China and India, whose economies are also major polluters, to play a role in reducing emissions.
Meeting on the scenic Japanese island of Hokkaido, the leaders also promised to make more immediate cuts in emissions over the next two decades, though they did not offer a specific numerical target. They indicated that they intend to write into the new treaty language that would bind them to "implement ambitious economy-wide mid-term goals in order to achieve absolute emissions reductions."
This is probably the only way we're going to get major emissions reductions; the politics of immediate cuts are just too ugly. Better to put it off until the current crop of negotiators is safely dead. When, likely as not, a new round of negotiators will vote to ignore them.