Rain for the first time on Greenland summit

The National Science Foundation's Summit Greenland Environmental Observatory. Peter West / National Science Foundation

 From EcoWatch

This past weekend, researchers at the National Science Foundation's Summit Station observed rainfall at the peak of Greenland's rapidly melting ice sheet for the first time on record — an event driven by warming temperatures.

"This was the third time in less than a decade, and the latest date in the year on record, that the National Science Foundation's Summit Station had above-freezing temperatures and wet snow," the National Snow and Ice Data Center (NSIDC) said in a press release earlier this week. "There is no previous report of rainfall at this location (72.58°N 38.46°W), which reaches 3,216 meters (10,551 feet) in elevation."

Temperatures at the summit of the ice sheet rose above freezing at around 5:00 am local time on Saturday, "and the rain event began at the same time," NSIDC noted. "For the next several hours, rain fell and water droplets were seen on surfaces near the camp as reported by on-station observers."

The anomalous rainfall at the ice sheet's peak marked the start of a three-day period during which "above-freezing temperatures and rainfall were widespread to the south and west of Greenland... with exceptional readings from several remote weather stations in the area," said NSIDC. "Total rainfall on the ice sheet was 7 billion tons."

The warmer-than-usual temperatures caused significant melting of the ice sheet, with melt extent peaking at 337,000 square miles on August 14.

"Warm conditions and the late-season timing of the three-day melt event coupled with the rainfall led to both high melting and high runoff volumes to the ocean," NSIDC observed. "On August 15 2021, the surface mass lost was seven times above the mid-August average... At this point in the season, large areas of bare ice exist along much of the southwestern and northern coastal areas, with no ability to absorb the melt or rainfall. Therefore, the accumulated water on the surface flows downhill and eventually into the ocean."

This is a major tipping point for sea level rise.  The highest point of the Greenland ice sheet is 3694 m (12119 ft).  Temperatures decline at roughly 6.5 degrees C per 1000 km of elevation, so at the peak of the Greenland ice sheet, temperatures should be +- 23 degrees C cooler than at sea level.  So if temperatures at sea level in Greenland are above 23 degrees C, then the Greenland ice sheet is going to melt even at the summit.  But if the summit starts to melt,  then it will shrink, and it will warm, slowly but inexorably.  So temperatures at sea level won't need to be so high for the ice to melt.  For example, if the summit shrinks just 100 metres, its temperature will (everything else be equal) rise by 0.65 degrees C or 1.2 degrees F.  So sea level temperatures of 23.5 will be enough to melt the summit.  And so more will melt, and so the summit will shrink further, starting a doom loop which leads to the Greenland ice cap totally melting.  

This will take hundreds, perhaps thousands of years, but the point is, once it's started, it won't stop.  Over the last 50 years the Arctic has warmed 3 degrees C even though the world has warmed by 1 degree C, because of its own doom loop: ever smaller and thinner summer sea ice contributes to the heating, because the ice reflects the sun's rays but dark seawater absorbs them.   And of course, this effect is far worse in summer, and we are now routinely getting Arctic heatwaves.  If/when  the Greenland ice cap melts, the sea level will rise 6 metres (20 feet).  And that's without taking into account the melting of the Antarctic ice cap.

You can kiss goodbye to most major coastal cities.