Ice Melt Series Part 1: Greenland’s Ice Sheet Melts at Record Rate

For a few days in mid-July, something happened on Greenland that hadn’t been recorded in more than three decades of satellite observation: nearly the entire ice sheet — from its thin coastal edges to its two-mile-thick interior — began melting at its surface, all at once.

A Scientist Who Didn’t Believe His Own Data

The discovery came almost by accident. Son Nghiem, a researcher at NASA’s Jet Propulsion Laboratory, was reviewing radar data from India’s Oceansat-2 satellite on July 12 when he noticed something startling: nearly all of Greenland appeared to be undergoing surface melt simultaneously. “This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?” Nghiem later said, describing his own skepticism about what his instruments were telling him.

Nghiem brought the anomaly to Dorothy Hall at NASA’s Goddard Space Flight Center, who confirmed unusually high surface temperatures using a separate instrument, the Moderate-resolution Imaging Spectroradiometer aboard NASA’s Terra and Aqua satellites. Two additional independent researchers — Thomas Mote at the University of Georgia and Marco Tedesco at the City University of New York — cross-checked the finding using yet another data source, passive-microwave readings from a U.S. Air Force meteorological satellite. All three independent instruments told the same story: this wasn’t a data error.

From 40 Percent to 97 Percent in Four Days

The numbers themselves are what make this event genuinely remarkable, not just to the public but to the scientists studying it. On July 8, roughly 40 percent of Greenland’s ice sheet surface showed signs of melt — already a substantial figure, but not unprecedented on its own. By July 12, just four days later, that figure had exploded to an estimated 97 percent. Satellite records stretching back more than three decades had never shown anything close to that extent of simultaneous surface melting across the entire ice sheet.

The event’s severity reached even Greenland’s highest, coldest point. At Summit Station, sitting roughly two miles above sea level at the ice sheet’s peak — a location so cold that even modest surface melt is unusual — temperatures rose high enough that ice there reportedly turned to slush, according to NASA’s own account of the event. Researchers attributed the extreme, rapid melt to an unusually strong ridge of warm air parked over Greenland, a weather pattern scientists have since taken to calling a “heat dome.”

What the Melt Doesn’t Tell Us — and a Real Scientific Pushback

Notably, NASA’s own scientists were careful to draw a distinction that got less attention than the headline figure: surface melt is not the same as ice sheet volume loss. Melting confined to the surface, especially at high elevations, frequently refreezes in place before it can run off into the ocean — meaning the 97 percent figure describes how much of the ice sheet’s surface experienced some degree of thaw, not how much total ice mass Greenland actually lost as a result. Researchers explicitly noted they had not yet determined whether this particular melt event would meaningfully affect the ice sheet’s overall volume or contribute measurably to global sea level rise.

That nuance became a genuine point of contention once the finding drew wider media coverage. Some glaciologists pushed back on characterizations of the event as unambiguously alarming, arguing that widespread surface melt events, while rare, aren’t entirely without precedent in Greenland’s longer climate history — ice core records suggest a comparably extensive melt occurred roughly once every 150 years on average, including one in 1889, well before industrial-era greenhouse gas emissions could plausibly explain it. That historical framing doesn’t erase the event’s significance, but it does complicate any claim that this single melt event, on its own, definitively proves accelerating human-caused warming rather than reflecting a rare natural weather pattern.

Part of a Broader Pattern, Even If This Event Alone Doesn’t Prove It

Whatever the ultimate cause of this specific July event, it arrived within a summer that would go on to set other polar records as well — Arctic sea ice extent would hit its own lowest point in the satellite record just two months later, in September. Taken individually, either event could plausibly be attributed to short-term weather variability. Taken together, across a summer that saw both Greenland’s surface ice and the broader Arctic sea ice pack post their most extreme readings in the modern satellite record, researchers argue the pattern becomes harder to dismiss as coincidence alone — the central question animating the second installment of this series.

This is Part 1 of our Ice Melt Series — see Part 2 on the record-low Arctic sea ice extent recorded two months later, or browse our full Environment archive.