Climbers on the Mer de Glace make their way through fallen rock debris resting on the glacier's surface. Sightseers and climbers take the Montenvers train from Chamonix to the Refuge du Montenvers which sits above the Mer de Glace glacier. The glacier is rapidly retreating due to climate change. The helicopter above is surveying the glacier's surface and is part of a research team documenting the glacier's retreat.