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Don Paul: Greenland's meltdown within a meltdown

The Greenland ice cap is melting in different places at different rates and, it turns out, in different ways.

How much of it will melt in the next century remains an open question.

The two least likely scenarios are the best (only minor additional melting) and the worst, in which we lose the whole ice cap. “The truth will lie somewhere in between” is a fitting cliché.

The worst scenario would have monumentally disastrous consequences. A City University of New York study found that 634 million people live in coastal locations less than 10 meters above sea level. If the entire Greenland ice cap melted, global sea level would rise by 21 meters, or just under 69 feet. Yes, there is that much ice up there. A climate scientist at Britain’s prestigious University of Reading believes there is a real chance of runaway melting in about 50 years as warming progresses.

His view has raised questions in peer review. One reason that worst-case scenario is probably unlikely is the impact of the sheer volume of fresh water that would be released over hundreds of years in such a meltdown. Such vast quantities of fresh water would dilute North Atlantic salinity to the extent of shutting down the conveyor current that drives the Gulf Stream. There is good evidence this has happened during past warmings. The collapse of the Gulf Stream would cool the climate of Europe, eastern North America and Greenland. (If you look at the latitude of Britain and many parts of Europe, you’d know the northern location of those population centers would be drastically colder without the Gulf Stream. Not a chance of Bordeaux grapes in Bordeaux without those warm waters.)

Before such a state of reduced salinity could be reached, however, sea level rises would still accelerate with large impacts on coastal regions and island nations. So, it’s vital to more accurately narrow the range of Greenland ice melt, since Greenland’s ice volume is second only to the much larger volume of Antarctic ice. The latter is melting faster around that continent’s edges, but Antarctica’s overall melt rate remains below that of Greenland.

A new NASA study determined that in Greenland’s two warmest summers on record, 2010 and 2012, the bellweather Rink Glacier melted in ways not known previously.

The ice not only melted faster visibly, but ice within the core of the glacier surged forward as a wave, underneath the surface ice. NASA described this solitary wave as akin to a freezer pop sliding out of its wrapper. This new discovery means there may be a mechanism by which Greenland ice can melt at a faster rate than in previous model projections, as was the case with the Rink Glacier. This glacier is one of Greenland’s major conduits to the ocean. In the early 2000s, it was releasing an average of 11 billion tons/gigatons of ice per year. That’s around the weight of 30,000 Empire State Buildings. But in the hot summer of 2012 this solitary wave mechanism added an additional 6.7 gigatons to the release. During the first three months of the peak melt season, the wave advanced at 2.5 miles per month. Then, in September, the wave accelerated to 7.5 miles in that month. NASA Jet Propulsion Laboratory scientists noted you could stand atop the glacier and be entirely unaware of this wave action in its core. They know the snow and ice melt are involved with the triggering mechanism to start such a wave, but the details of what starts this wave are still uncertain. There is probably a lubrication factor provided by snow and ice melt. During the cold months, ice from the interior surged forward to replace the lost ice mass from the solitary wave.

As the climate continues to warm, the solitary wave phenomenon would probably become more common, and the overall loss of ice mass on Greenland would then accelerate beyond climate model predictions which did not include this then-unknown mechanism.

In the meantime, NASA continues thorough analysis of the ice cap and the loss of mass from both Antarctica and Greenland.

So, while that worst case scenario of a total meltdown remains unlikely, the “truth lying in between” shouldn’t provide a false sense of comfort.

NASA has an extensive dataset on melting from many types of sensors, including ground stations and high resolution satellite data.

It is clearly in our interest to get a better handle on the most likely range of ice melt in the next 30 to 100 years.

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