Wall Street Journal: In the weeks leading up to the Copenhagen climate conference, countries from China to Singapore have pledged cuts to their greenhouse-gas emissions. One question still lurks unanswered: Who is going to pay for it? Cutting carbon costs money. Factories must be retrofit and industries must be prodded to buy more-expensive green technology. Estimates for the annual tab in developing countries vary widely, but could reach EUR100 billion ($150 billion) by 2020, and poorer nations …