The downfall of Glacier Bay’s namesake attractions is what uplifts the tourists who perch along boat railings below the glaciers. With the incandescent blue walls of the Margerie Glacier poised 100 feet (30 m) overhead, we await with bated breath a signature event that may or may not presage a catastrophe for human civilization.

Squealing gulls wheel by. Clouds dash against the near ridges of Alaska’s Fairweather Range. A whisper of chilled air washes across the 200 feet (61 m) of water that separates our tour boat from the toe of the glacier.

And then a small spire of ice peels away from an inner crevice, dropping into the water inside an ice cave with a slap that echoes to the boat a second later.

A view of the Johns Hopkins Glacier on a rare sunny day

My fellow visitors sigh with satisfaction, even clapping, as if the glacier had calved off that tiny piece just for our entertainment. Cameras flash, too late, though the scene itself is memorably otherworldly.

Smiles all around, and a lady next to me turns to offer a happy remark. “Pretty cool!” Not every tour gets to see the glacier shed, our guide has told us. We’re lucky.

Whether we are truly lucky, though, depends on whether you take the short or long-term view. There’s a chance we are celebrating an infinitesimal crack in the climatic dike that holds back the oceans from about half of humanity.

Like most ice around the world, Glacier Bay’s has been receding, and the tiny piece that dropped before our eyes may have raised ocean levels a nanometer higher. I live near sea level in Seattle; witnessing a glacier calve is a fine sight, yes, but also mildly disconcerting.

Touring the marine wilderness of Glacier Bay, one of the best-known and most-visited locales in Alaska that became a National Park in 1980, is a three-dimensional experience. The scenery is sensational, with snow-draped peaks towering over sparkling fiords. Wildlife abounds, from sea birds to shore-bound brown bears. And it affords a sobering chance to think about climate change.

This 63-mile (101 km) inlet, tucked into the northwest corner of southeast Alaska (which Alaskans simply call “Southeast”), was completely encased in glacial ice when English navigator and explorer George Vancouver first sailed by in 1794. The 400-foot-thick (122 m) wall of ice was 20 miles (32 km) wide and more than 100 miles (160 km) long.

It’s been receding ever since; when naturalist John Muir visited in 1879 it had retreated 48 miles (77 km). In 1916 it was 65 miles (105 km) shorter. Today it is almost completely back onto dry land, with just a few spurs hovering above saltwater. Scientists are studying the phenomenon, “hoping to learn how glacial activity relates to climate changes,” as the National Park Service euphemistically puts it.

Funny, the glacier’s retreat and the growth of the Industrial Age correspond almost exactly. Must be a coincidence.

But climatic and geologic changes do not always produce the local results you expect. While the world’s oceans are almost undoubtedly on the rise, in the short term the geography of the Glacier Bay landscape is experiencing the opposite effect.

As the glacier’s immense weight recedes, the land itself is rising. The chief beneficiaries are landowners in Gustavus, the town that perches at the head of Glacier Bay on one of the few flat plains in Southeast Alaska. As the land rises, they gain new property that once lay underwater.