Reuters: Developing nations may need to slow projected growth in their carbon emissions by 15 percent by 2020 if rich countries agree to reduce theirs by up to 40 percent for a new global deal, a top U.N. official said on Thursday. Negotiations for a global deal to fight climate change, to be agreed in Copenhagen in December, have stumbled on the question of levels of emission cuts to be taken by rich states and developing nations. A U.N. climate panel report in 2007 said that cuts …