"At first, we didn't believe it." Indeed, the data presented to NASA glaciologist Ala Khazendar and colleagues regarding Jakobshavn Glacier was almost unbelievable. For 20 years, Jakobshavn has been Greenland's fastest-thinning and fastest-flowing glacier. Its thickness shrank 500 feet from 2003 to 2016. But since then, it's been advancing toward the ocean, growing thicker, and—though still contributing to sea level rise, as more ice is lost to the ocean than gained from snow—it's losing less ice than expected, according to NASA's Oceans Melting Greenland project. In a study published Monday in the Nature Geoscience journal, Khazendar explains the likely cause: the North Atlantic Oscillation, a climate pattern that causes the North Atlantic to transition between warm and cold every five to 20 years.
With a recent shift into the cold phase, the Atlantic Ocean was cooled overall, while an ocean current reaching Jakobshavn's ocean face lowered the temperature of surrounding waters by more than 2.7 degrees Fahrenheit—to its coldest level since the mid-1980s. It's been that way for the last three summers. As study co-author Josh Willis puts it, per Live Science, "Jakobshavn is getting a temporary break from this climate pattern." While he notes other Arctic glaciers could be experiencing growth, he's not jumping for joy. "We know in the long run, this cooling is going to pass," he tells National Geographic. "When it does, the glacier is going to retreat even faster than it was before." Khazendar is equally cautious. "All this is an indicator of how sensitive glaciers are to ocean temperatures," he says. (Much more on the topic here.)