It took decades for negotiators to write treaties that curb nuclear warheads. By that measure, efforts to limit global warming may just be getting started. United Nations climate talks starting in Mexico next week are expected to be an ongoing process. "We've been at it for 18 years on climate change, but that's not unique," Duncan Hollis, associate professor at Temple’s Beasley School of Law and editor of the forthcoming Oxford Guide to Treaties. "Breaking this up into smaller pieces and trying to knock off one piece at a time is certainly worth trying."