Sea ice turns out to be one of the most misunderstood characters in the climate story. Sitting aboard the icebreaker Araon, I ask New York University climate scientist David Holland a deceptively simple question: What exactly is sea ice?
Holland’s answer cuts straight through the confusion. There are two kinds of ice on Earth. Sea ice forms when the ocean freezes—just like a pond in winter, except it’s saltwater. Land ice, by contrast, is what we usually picture in Antarctica: snow piling up over thousands of years, compacting into glaciers that are miles thick. That distinction matters. When sea ice melts, sea level does not rise. When land ice melts, it absolutely does.
For our mission, sea ice matters for a different reason: it stands between us and Thwaites Glacier. At this time of year, nearly 90 nautical miles of it.
Holland explains that temperature alone can grow about a meter of sea ice in a winter. But wind is the real sculptor. Winds can crush ice together into towering ridges—or pull it apart into narrow openings called leads, which ships desperately search for. Where Shackleton once relied on a lookout in the crow’s nest, today’s captains use satellites.
Those satellites don’t just “see” ice. They detect naturally emitted microwave radiation from the surface, allowing scientists to map ice concentration through clouds and darkness. Laser altimeters add another layer, measuring how much ice sits above the water—its “freeboard”—to infer total thickness.
The big picture Holland lays out is sobering. Arctic sea ice has already lost about half its summer extent. Antarctic sea ice lagged behind—but over the past five years, it too has begun to decline.
For us, the question is immediate and practical: will the ice open long enough to let us through? The answer, Holland says with a shrug, is about fifty-fifty. In polar waters, that’s as precise as certainty gets.
