From the offices of the fishing operation founded by his family two generations ago, Adalsteinn Ingólfsson has watched the massive Vatnajökull glacier shrink year after year. Warmer temperatures have already winnowed the types of fish he can catch. But the wilting ice mass, Iceland’s largest, is a strange new challenge to business.

“The glacier is melting so much that the land is rising from the sea,” said Mr. Ingólfsson, the chief executive of Skinney-Thinganes, one of Iceland’s biggest fishing companies. “It’s harder to get our biggest trawlers in and out of the harbor. And if something goes wrong with the weather, the port is closed off completely.”

A warmer climate isn’t just affecting Höfn, where the waning weight of Vatnajökull on the earth’s crust is draining fjords and shifting underground sediment, twisting the town’s sewer pipes. As temperatures rise across the Arctic nearly faster than any place on the planet, all of Iceland is grappling with the prospect of a future with no ice.

Energy producers are upgrading hydroelectric power plants and experimenting with burying carbon dioxide in rock, to keep it out of the atmosphere. Proposals are being floated for a new port in Finnafjord, now a barren landscape in the east, to capitalize on potential cargo traffic as shipping companies in China, Russia and Arctic nations vie to open routes through the melting ice. The fishing industry is slashing fossil fuel use with energy-efficient ships.

Glaciers occupy over a tenth of this famously frigid island near the Arctic Circle. Every single one is melting. So are the massive, centuries-old ice sheets of Greenland and the Polar regions. Where other countries face rising seas, Iceland is confronting a rise in land in its southernmost regions, and considers the changing landscape and climate a matter of national urgency.  […]