As the heat wave that struck the southeastern United States made its way up to Greenland, the ice-covered island recorded over 2 billion tons of ice melt in just one day.
Greenland, which sits in between North America and Europe in the northern Atlantic Ocean is covered with snow year round. Historically, from June through August the island experiences a net loss in ice as warmer summer temperatures melt glacier snow/ice into the North Atlantic Ocean.
This average melt season has been expanded lately as melt days occur earlier in the year and large melt events are more regular. On June 13th melting exceeded 2 gigatons (4 trillion pounds), which is very unusual for this early in the summer. Typically, the largest melt events occur in July and don’t reach this magnitude.
What Caused The Extreme Melting In Greenland
Melting in Greenland this season began early and strong. This is because there has been a persistent high-pressure ridge along eastern Greenland. This high-pressure ridge is responsible for warm central Atlantic air masses around Greenland and clear, sunny skies.
In addition, the high-pressure front that caused an early season heat wave in the southeastern United States has now made its way to Greenland. These two high-pressure systems combined have led to unusually warm and sunny conditions in Greenland and unusually high melting.
As Greenland ice continues to melt it perpetuates a positive feedback loop. Ice has a high albedo (close to 1), which means it reflects back the vast majority of the sun’s solar radiation and with it heat. You’ve experienced this if you’ve walked down the road barefoot on a hot summer day. The black asphalt is much hotter than the white concrete sidewalk. This is due to the difference in how much solar radiation white versus black reflects. Hence, as Greenland melts more of its ice, the surface is converted from a high albedo white to darker colors. This, in turn, causes more melting and adds to the positive feedback loop.
Is the Greenland Melting Unprecedented?
To put this singular massive melting day into perspective the best year to compare this to is 2012. There was a similar scenario in 2012 where a persistent high-pressure system sat over Greenland for much of the summer. This causes record-breaking melting in 2012 across Greenland and at one point 97% of the entire island’s ice sheet was melting.
The early and unusually high melting in 2019, along with similar weather patterns has led meteorologists and climatologists to believe we are in for another record-breaking summer of melting.
The Polar Portal has several great figures/graphs that visualize the current state of Greenland’s ice.
The figure above is broken into a map and a graph of melting versus average. The top map shows locations of melting, which is clearly concentrated on the coasts and specifically the Northern, Western, and Southern coasts.
The graph below shows mean 1981 to 2010 melting in Greenland. You can see the melting beginning in early April and ending in late September with June through August as the core melting months. Compared to historical average, this years melting (blue line) has the sudden and dramatic spike corresponding to the melting last week. This spike would be on the high side for the peak melting times of mid-July and is very unusual for mid-June.
This all points to likely another record melting season in Greenland and with it higher sea levels. Greenland is a significant contributor to sea level rise and this is yet another indication that we’re on an overall melting and accelerating trend.