A small European capital that has about the same population as the Des Moines metro — led by an activist mayor whose first name also happens to be Frank — is taking some bold steps to cancel out its greenhouse gas emissions. By 2025, Copenhagen, a once-grimy industrial city in Denmark, aims to be net carbon neutral, meaning it plans to generate more renewable energy than the dirty energy it consumes. With the vast majority of planet-warming emissions coming from cities, the big solutions for climate change need to come from cities, too, as this New York Times article says. Read how the city has already cut its emissions by more than 40 percent from 2005 levels, and how it plans to reach its 2025 goal.