November 12, 2015:
North, south, east, and west. At all points of the compass, the entire outer edge of the Greenland Ice Sheet is flooding into the oceans with increasing velocity. For NASA it’s the absolute worst kind of OMG realization. For the world’s warming oceans and airs are clearly worsening an already visible Greenland melt. And a new report just out of the University of California (Irvine) today shows that a massive glacier containing enough water to raise seas by more than 1.6 feet (0.5 meters) is the most recent of a growing number of these ice giants to initiate a swift rush into the ocean.
Called Zachariæ Isstrøm, this enormous glacier dominates a large section of the northeast-facing shores of Greenland. The glacier, hundreds of feet tall and plunging hundreds more feet below the ocean surface, like many in our world, now faces the combined threat of warming airs and waters. A double insult that, according to researchers, over the past 15 years has led to first destabilization and then a rapid seaward acceleration.
(1975 to 2015 time lapse shows recent rapid retreat of the Zachariæ Isstrøm glacier’s front. The dark green line marks the 2003 extent of the glacial front. Note the rapid retreat through 2015 in lighter shades blending toward white. Image source: Jeremie Mouginot/UCI via Climate Central.)
According to the new study — Fast retreat of Zachariæ Isstrøm, northeast Greenland — published today in Science, the glacier’s rate of seaward movement has tripled in velocity even as the pace of ice thinning along its grounding line doubled:
Warmer air and ocean temperatures have caused the glacier to detach from a stabilizing sill and retreat rapidly along a downward-sloping, marine-based bed… After 8 years of decay of its ice shelf, Zachariæ Isstrøm, a major glacier of northeast Greenland that holds a 0.5-meter sea-level rise equivalent, entered a phase of accelerated retreat in fall 2012. The acceleration rate of its ice velocity tripled, melting of its residual ice shelf and thinning of its grounded portion doubled, and calving is now occurring at its grounding line.
In total, more than 4.5 billion tons of ice is now estimated to be flooding out from this glacier and into the ocean each year. That’s a mountain of ice about 4.5 cubic kilometers in size hitting the world’s waters from just this single glacier every time the Earth completes one circuit around the sun. In other words, Greenland just opened a new floodgate to the North Atlantic. Researchers publishing the study estimate that it will take between 20 and 30 years for the glacier to melt back to an underwater ridge line that should somewhat slow its melt. But the real news here is that a human-forced warming of the globe has set a monstrous pile of ice, once thought stable, into a motion that will result in yet more global sea level rise.
To the north of Zachariæ Isstrøm sits the also melting Nioghalvfjerdsfjorden. A giant of ice in equal volume to that of Zachariæ. Nioghalvfjerdsfjorden sits on an upward sloping bed and so is not as subject to rapid destabilization as Zachariæ. However, the study found that the combined total ice mass of both glaciers in the range of 1 meter worth of sea level rise was now involved in a significant melt that would “increase sea-level rise from the Greenland Ice Sheet for decades to come.”
(Map of Greenland topography showing large sections of the interior resting near or below sea level. As a result, warming waters have numerous avenues for invasion into the Greenland Ice Sheet. Numerous ways to melt Greenland ice from below. Zachariæ Isstrøm covers the upper right hand section of this image — sitting astride a low elevation channel the plunges deep into the heart of the current ice mass. Image source: Livescience.)
Greenland is the last major remaining bastion of glacial ice in the Northern Hemisphere. Surrounded on all sides by warming airs and waters, it is the most vulnerable large ice mass to the forces set in play by a human warming of the global environment. In total, Greenland holds enough ice to raise seas by 23 feet. And, in the geological past, just 1.5 to 2.5 degrees Celsius worth of temperature increase above Holocene averages was enough to melt much or all of it.
Currently, human warming by Greenhouse gasses has pushed global average surface temperatures into a range about 1 degree Celsius hotter than the 1880s. It’s a temperature running into ranges that are now comparable with the Eemian — the interglacial period that occurred between 115,000 to 130,000 years ago. A period when oceans were about 13 to 20 feet higher than they are today.
But perhaps even more concerning is the fact that global greenhouse gas concentrations in the range of 400 ppm CO2 and 485 ppm CO2e are enough now to warm the Earth by 2 to 4 degrees Celsius long-term. It’s a heat forcing that would likely spell the end for Greenland’s ice if it remained in place for any significant period. A heat forcing more comparable with Pliocene and Miocene ranges when the world’s glaciers were even more greatly reduced and seas were 30 to 130+ feet higher than they are presently.
Unfortunately, what the building global heat and currently very high greenhouse gas heat forcing means is that the Earth System will continue to accumulate warmth for some time. And as this happens more and more glaciers — both in Greenland and Antarctica — are going to destabilize, speed up, and contribute increasing melt volumes to the world ocean. Eliminating greenhouse gas emissions at this time and pushing to return to atmospheric levels in ranges below 350 ppm CO2 is therefore absolutely necessary if we are to have much hope of preventing ever-worsening rates of glacier destabilization and related contributions to sea level rise.
Hat tip to Todaysguestis
Hat tip to Colorado Bob
Hat tip to Ryan in New England