Protests rocked Copenhagen this week, but I’ll leave them to the mainstream media and instead focus on acting locally. Many municipal mayors are showing up in Copenhagen. At first I thought they were just jumping on the bandwagon, but I soon discovered they're taking part in a parallel summit organized by local and regional governments from around the world. Cities are immensely important to reducing carbon emissions, and I spoke with Hugh Bartling, a public policy professor at Depaul University in Chicago, who explained just what kind of impact they have. "Fifty percent of the world’s population are in cities, and by 2050, it’ll be 80 percent," Bartling says. "If you think about it, most of the actual policy implementation happens at local levels in a lot of places, both in the industrialized world and the developing world." That means that if world leaders ever strike a climate treaty to curb greenhouse gas emissions, it will be cities ensuring the carbon reductions are made and footing the bill to boot. That's why city representatives are here (NYC’s Bloomberg arrived on Tuesday) making sure that their views are heard. But they have their work cut out for them. "It’s heads of states that negotiate treaties, not mayors," Bartling says. Mayors in developing countries have even more incentive to demand that cities are mentioned in any new treaty, since it could help them get the cash they need to implement systems to both adapt to climate change and reduce emissions. "What local officials really want to see is something in the text that acknowledges local authorities and local government," Bartling says. "What that means is that whatever deal is hashed out in the developing world, mayors can go to their national government and say, 'we need to have aid money coming into the cities.'" Cities also have control over buildings, which account for more than 30 percent of greenhouse gas emissions worldwide. Cities could slash these by changing zoning codes and ordinances, says Bartling. A recent Finnish study showed that 95 percent of the world’s buildings that will exist in 2050 have already been built. Cities wield the power to put measures in place to save energy in these aging buildings, such as insisting on better insulation, for example. Bartling says he will have his eye on how suburbs will adapt to reducing emissions under a global climate treaty. He has studied how sprawl developed in the U.S. and Canada, written a book about it and was even called on by the Canadian government to work on how to transform suburbs in Toronto. "In Canada and the U.S., most of the population growth happened after World War II and there was no real concern with climate change," Bartling says. "The assumption was limitless amounts of fossil fuels." This has created the toils of suburban life, which Bartling can distill down into a sentence. "You work here, you shop there, you live here and we all crash and there's huge congestion and it screws up air quality." Bartling has also studied sewage and said it's one of his favorite topics, but I declined to follow up. Check back soon for more reports from Copenhagen.