By offering concrete emission targets last week, the United States and China have resuscitated global climate talks that were headed toward an impasse. But the details that have yet to be resolved -- including the money that industrialized countries would offer poorer ones as part of an agreement -- suggest a political deal remains a heavy lift for the 192 countries set to convene in Copenhagen in little more than a week.

Negotiators aim to produce a blueprint for a legally binding international treaty that would replace the Kyoto Protocol when it expires in 2012 and govern individual countries' greenhouse gas emissions.

Although the proposals from the world's two biggest greenhouse-gas emitters have boosted the prospects for a deal, they demonstrate something else as well:...