FROM ABOVE, ICELAND'S VATNAJÖKULL, an ice cap bigger than Delaware, looks like a giant Rorschach butterfly—fitting for something steadily winging it from the earth. Doubly menaced by global warming above and active volcanoes beneath, the Vatnajökull has molted roughly 235 square miles since 1958.

It heaved into view as we rounded a curve. Spilling from between a pair of russet crags, the dirty tongue of ice had a roasted look about it, like a charred marshmallow, pallid innards oozing forth.

"Glorious," said Dad. "Let's climb the son of a bitch."

"I'll stay here," said Dan.

"But don't you want to see it before it melts?" I said.

"It isn't melting," he said, quoting an outdated and patently false passage from the guidebook, which claimed that the Vatnajökull was one of the few glaciers on the planet that was actually on the grow.

I gritted my teeth, Dad gave a glum shrug, and the two of us set off.

A sign hammered beside the path warned us that setting foot on the ice without an experienced guide might land you at the bottom of a crevasse. I paused.

"What should we do about this sign?"

"I intend to ignore it entirely," said Dad.

"Spoken like a man with diminished life expectancy," I said.

Dad began picking his way with surprising ease to a promontory atop the ice slope. He stood with his hand on his hip, looking as though he wished he had a flag to plant. I chose a path that looked less risky but twice fell to my knees.

When I'd clawed my way to Dad's side, he was staring down at the lagoons of glacial melt at the bottom of the grade. The water was a swirled gray and blue, the color of moonstone, the oddly lovely symptom of a glacier in decline.

"A century ago, this ice went on for miles, all the way to the sea," I said, paraphrasing a newspaper story I'd come across.

"It's grim to think about what'll be here a hundred years from now," said Dad. "Trailer parks, Disney World Iceland. In the grand scheme of things, this isn't the worst time to be facing one's mortality."

The wind poured down off the glacier, rinsing us in the cleanest, coldest air I've ever breathed, air you could sell by the gallon in Malibu. We stood silent for a long moment, struck dumb by the wind, the ice glowing under our boots, the bright emptiness of the world around us. No planes or distant interstates sullied the silence.

"Isn't this religious?" my father said.

"It really is."

In the distant parking lot sat the car, its windows fogging up.

"Too bad Dan didn't come out," I said.

"It's a shame, a real sadness," said Dad, "but he's really doing his best to have the non-experience of a lifetime."

But Dan had done us a service: He'd become the living emblem of all that would go wrong on this trip. We stood at peace on the glacier's nose and inhaled eternity.