In Mexico, delegates from more than 190 countries are gathered for U.N.-led talks on setting rules to limit global warming. A year ago in Copenhagen, delegates failed to draft a treaty, leaving in limbo the 1997 Kyoto accord that mandated cuts in carbon-dioxide emissions until the end of 2012. "We’ve been at it for 18 years on climate change but that's not unique," said Duncan Hollis, an associate professor at Temple's Beasley School of Law. "Breaking this up into smaller pieces and trying to knock off one piece at a time is certainly worth trying."