Chamonix was one of the original alpine resorts. Until about the year 1800, people didn't climb, or hike, or even paint mountains much. Mountains were a pain. Then, in the 19th century, the Romantic movement had people all across Europe communing with nature.

Eventually engineers constructed a state-of-the-art array of trains and lifts to get the influx of nature-hungry city folk high into the mountains with ease. One of the first, this two-car cogwheel train — inaugurated in 1909 — transported turn-of-the-century visitors to the edge of the Mer de Glace glacier. And it's thrilling visitors to this day.

This train was built over the objection of a couple hundred mule owners who figured it would put 'em out of business. I'd say they were probably right.

The Mer de Glace is France's largest glacier — four miles long. In the 1600s, the glacier extended much farther downhill — actually threatening to block off the valley. But now, it's going in the opposite direction: receding — dramatically.

When we travel, we see and experience vivid examples of climate change. For me, this shrinking glacier is one of the most poignant. When I first came here, back in the '80s, the Mer de Glace was hundreds of feet higher than it is today.

From up above, on the observation deck, it's hard to imagine that just a few decades ago the glacier was so much higher, nearly filling this narrow valley. A cable car descends, taking visitors closer to the glacier. From there, the hike down to the receding "sea of ice" gets longer each year. Disturbing markers show where the glacier was just a short time ago. A touristy tunnel is carved deep into the ice. Hiking into it, you find yourself in a cool, dripping world of translucent blue. And, on an ice carving meant to call attention to climate change, tourists pose obliviously.