Interesting data from the Congressional Budget Office:
"In the absence of any change in policy, CBO projects that in 2020 total U.S. emissions will be about 7,580 million metric tons of carbon dioxide equivalents; emissions by entities that would be covered under the two cap-and-trade programs would account for about 6,550 million tons, more than 85 percent of total U.S. emissions....total emissions of the covered entities in (2020) would be about 5,830 million tons, 720 million tons (or 11 percent) below the amount anticipated under current law. (That percentage would increase to about 53 percent by 2050.)"

Translation: under the current iteration of the Waxman-Markey bill, CO2 output by the United States would be reduced by 11% of United States "man-made" sources (power plants, industry, cars, trucks, etc). Sounds like some real progress?
Well, according to the Energy Information Administration (an agency within the federal Department of Energy) world-wide "man-made" emissions are anticipated to be 35.4 BILLION TONS. So - the reduction in U.S. C02 works out to be ... 2% of "man made" worldwide emissions. Hence why opponents of "cap and trade" say that it is meaningless to burden the American economy with the costs associated with the regulatory regime if developing nations (e.g. China & India) are not going to join in.

Then there's this whole issue of carbon contributions from "other" sources (livestock, volcanic activity) that contributes nearly half of all annual contributions. Throw those in there and the U.S. reductions will be less than 1% of worldwide emissions.
The costs, however, the American people will remain the same. Hence why we've said its like paying thousands of dollars over our lifetimes to keep a thimble full of water from being poured into the Ohio River. That's insane.