3. New York, United States
The most populous city in the US takes the bronze medal for carbon footprint. In January, the iconic metropolis sued the world's five largest oil companies — BP, Chevron, ConocoPhillips, ExxonMobil and Royal Dutch Shell — for their contribution to climate change and its effects on the city. The city has been intensively working to reduce its emissions, but still has a lot of work to do.