Icebergs in Disko Bay, Greenland.
A thousand feet above the glistening, iceberg-dotted water of the ocean off of East Greenland, oceanographer Josh Willis braces for balance, his feet spread wide on the metal floor of a specially-outfitted airplane. He grips a wide grey cylinder, hovering it over a 6-inch-wide bottomless tube.
The pilot’s voice crackles over the intercom: “3, 2, 1, zero, DROP.”
Willis lets the cylinder go. With a whoosh, it slips down the tube and into the wide-open air.
The plane banks hard to the right and everyone on board rushes to a window. “I see it!” yells Ian Fenty, another oceanographer on the project, as the probe—designed to sink to the seafloor and record the properties there—splashes down.
Willis, Fenty, and a crew of other scientists and pilots are flying the edge of Greenland’s vast ice sheet to figure out how the ocean eats away at the ice, speeding or slowing its slide into the water, where it melts, raising sea levels worldwide.
But exactly how much ice it will deposit, and how fast, is still an open question. Greenland is currently the biggest contributor to global sea level rise. By 2100, will its ice sheet’s melt add inches to the world’s oceans—or will it add much more?
That’s a trillion-dollar question. Nearly 70 percent of Earth’s population lives within 100 miles of a coast, and vast amounts of infrastructure—from airports to ports to cities to roads to Internet cables—sits in zones that could flood within decades. Small, low-lying island nations, city...