Chamonix, France
Credit: Christian Kober / Getty Images

Chamonix's historic Mer de Glace glacier has lost 250 feet in thickness in the past 20 years. Two-thirds of ski resorts in the Alps are expected to close by 2088.

What they're doing: Chamonix is attempting to reduce its greenhouse gas emissions 22 percent by 2020, in part by banning polluting trucks from the Mont Blanc tunnel, reducing speed limits, and increasing service on the St-Gervais-Vallorcine train line.