Staggering extent of melting on Greenland ice sheet because of heat wave

A record-setting European heat wave hit Greenland, causing a major melt on 60 percent of its ice sheet. (Associated Press/Caspar Haarløv “Into the Ice”)

A major melt event on the Greenland ice sheet, the most extreme since 2012, has left its surface transformed. Pools of sapphire melt water have popped up like pimples, while the usual pristine blanket of fresh snow atop the ice sheet has vanished over large areas, replaced by ash-colored ice left behind nearly 20,000 years ago.

The melt event was spurred by the same record-breaking heat wave that scorched Europe in late July, setting national temperature records in the United Kingdom, Germany, the Netherlands and Belgium. The pulse of warmth pushed temperatures 15 to 30 degrees above normal, and in response, the ice sheet has released billions of tons of water from surface melting.

Melting occurred on 60 percent of the ice sheet on Wednesday, making it the biggest single-day melt event since July 2012, when 97 percent of the ice sheet saw melting.

We created animations that show the change in the condition on sections of the ice sheet between July 30 this year and one year ago around the same time. Last summer was a relatively cool season, with lower ice loss than had been seen in some previous years, but even with that caveat, these comparisons are jaw-dropping.

Satellite views of a northeast section of Greenland comparing summer 2018 with summer 2019, after a major melt event. (Sentinel 2/ESA)
What stands out in both of these animations is the explosion in the amount of area colored in blue, revealing substantially increased melt water accumulating on the surface, as well as melt ponds.

In some areas, this melt water is gushing, cutting out crevasses and forming raging rivers. Studies have shown that melt water from the surface can work its way deep into the recesses of the ice sheet, lubricating the bottom of some glaciers and thereby speeding up the loss of ice mass.

Detailed satellite imagery from Planet Labs Inc. from the past month shows just how quickly one of these melt water pools formed in northeast Greenland:

The emergence of a melt pond over northeast Greenland in July 2019. (Planet Labs Inc.)
In addition to the melt ponds, what also jumps out in the animations from the Sentinel 2 imagery is the big year-to-year transformation in the color of the ice sheet’s surface, from white to gray in many areas. The darkening of the ice surface speeds up melt, since it causes the ice to absorb more incoming solar radiation.

The loss of snow on the ice sheet began in the spring. The winter was relatively dry, particularly in southwest Greenland.

“The thin snow and spring warming led to a loss of snow and firn, exposing a much greater area of bare ice,” explained Thomas Mote, a professor of geography at the University of Georgia. “The exposed ice is much darker than the winter snow cover.”

Jason Box, a climate scientist who studies the ice sheet, said this loss of spring snow made it apparent by May that a major melt event on the ice sheet was likely this summer. The depleted snow cover meant there would be “less of a shield [to] buffer the abnormally high air temperatures,” he wrote in an email.

The bare ice exposed by the melted snow is thought to be a layer of glacial era ice that appears gray because it’s rich in dust, according to climate scientist Ruth Mottram of the Danish Meteorological Institute. “It then acts as a source of nutrients for all sorts of biology — primarily bacteria and algae that cause further darkening,” she said.

Mottram says that rainfall also contributes to this darkening process. “I have seen glaciers being washed clean by rainfall in the middle of the melt season, so I suspect the very dark color this year is partly a result of the long warm period and the long dry period,” she said.

The southwestern Greenland animation also shows significant changes from 2018 to 2019 in the calving along the edge of the ice sheet at the coast, where it sheds giant pieces of ice.

“The calving front is very interesting,” Mottram said. “It looks like it has retreated and is calving bigger and more regular shaped icebergs this year. There is a link between melt rates and calving rates so it’s not surprising, but the shape of the fractures with more regular parallel crevasses suggests to me the glacier velocity has increased, possibly as a result of the long melt season.”

In other areas, satellite imagery reveals an active wildfire and a burn scare from a separate wildfire two summers ago:

To scientists who study the ice, often traveling there each spring and summer to gather data, this week’s melt event demonstrates the increased pace of ice loss as a result of human-caused global warming, along with other factors.

Studies have shown that extreme ice melt periods like the one seen in 2012 typically occur about every 250 years, so the fact that another one is taking place only a few years later could be a sign of how climate change is upping the odds of such events, too.

What happens in Greenland may seem remote and disconnected from our everyday lives, but the ice sheet is already the biggest contributor to modern sea level rise and the medium and long-term viability of cities like Miami, New York, Norfolk and many others depends in part on the pace and severity of ice melt during the next few decades.

Every increment of sea-level rise provides a higher launchpad for storms to more easily flood coastal infrastructure, such as New York’s subway system, parts of which flooded during Hurricane Sandy in 2012. Think of a basketball game being played on a court whose floor is gradually rising, making it easier for shorter players to dunk the ball.

According to Mottram, the ice sheet sent 197 billion tons of water pouring into the Atlantic Ocean during July alone. This is enough to raise sea levels by 0.5 millimeter, or 0.02 inches, in a one-month time frame, said Martin Stendel, a DMI researcher.