150 years ago, even to the edge of the village of chamonix where we came from this morning. >> they could see this glacier from town. >> yeah. that's right. so the changing front of the glaciers, which is happening, did not need any precise survey. the farmers could see that. >> they don't need thermometers here, right? >> not at all, no. because glaciers are probably one of the most sensitive indicators of climate change. >> right. so roughly, i mean, it's a rough approximation, but at the time the united states was born -- >> yeah. >> -- we could almost step out. >> that's right. >> in the year 1800 and walk on top of it. but now, obviously, it is not only shrunken below, but way up there. >> but even 20 years ago, 30 years ago precisely, the size of this glacier was 60 meters higher. so i can see with naked eyes