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In 70 years, holding the Winter Games in Sochi would be entirely impossible, according to a recent study looking at climate change's impact on the current and former Olympic sites. Even now, Sochi, which is technically a subtropical region, has struggled with keeping enough snowpack for the Games. 

What they've done: Sochi is a small winter resort that had to scale-up big this year – costing an estimated $51 billion, thanks in large part to the biggest artificial snow-making system in the world. To get snow to the slopes, Russians have had to move water up the mountain with some 400 generators, tapping into two new reservoirs, a move that environmentalists argue may cause ecological damage to the regions for decades to come.