According to a new report, the Greenland Ice Sheet lost one trillion tons of water due to melt during the four-year period from 2011 through 2014. That’s about double the typical rate of loss during the 1990s through mid-2000s. Subsequently, Greenland’s contribution to sea-level rise also doubled. As a result, Greenland alone contributed 0.75 mm of sea-level rise every year during the 2011 to 2014 period.
(The above video briefly explains the findings of a new scientific study indicating a doubling in the rate of Greenland melt during 2011 through 2014.)
Bear in mind, the study focuses on Greenland only. Those numbers don’t include thermal expansion from the world’s warming oceans. Nor do they include an increasing amount of melt from Antarctica. Nor do they include large volumes of melt coming from the world’s rapidly disappearing mountain glaciers. Together, all of these in total are pushing sea levels higher by around 4 mm per year during the 2011 through 2016 period. That’s about 1 mm more per year than the 1993 to 2009 period. But the greater additional contribution appears to be coming from melting glaciers in Greenland and Antarctica.
The new Greenland Study found that melt averaged around 250 billion tons per year over the four-year period. This included a single melt year, 2012, in which Greenland contributed about half a trillion tons of melt water. The massive 2012 melt was spurred by high Greenland surface temperatures during summer which resulted in spiking surface melt rates during June, July, and August. At the time, a powerful high pressure system focused heat across the ice sheet which caused most of the surface area of Greenland’s glaciers to experience melt.
During 2011–2014, Greenland mass loss averaged 269 ± 51 Gt/yr. Atmospherically driven losses were widespread, with surface melt variability driving large fluctuations in the annual mass deficit. Terminus regions of five dynamically thinning glaciers, which constitute less than 1% of Greenland’s area, contributed more than 12% of the net ice loss. This high-resolution record demonstrates that mass deficits extending over small spatial and temporal scales have made a relatively large contribution to recent ice sheet imbalance.
In other words, melt at the margins of the ice sheet and large surface melt pulses during brief periods were the primary contributors to increasing melt rated during the study period.
(Annual mass losses from Greenland and Antarctica are accelerating. This results in increasing rates of global sea level rise. While mass loss in Antarctica has recently primarily been driven by basal melt, surface melt has been the chief contributor to Greenland mass loss. In addition, the highly variable nature of surface mass loss along with its tendency to create brief, intense melt pulses is some cause for concern. Image source: Charting Ice Sheet Contributions to Global Sea Level Rise.)
The study found that surface melt rates were highly variable and dependent upon weather — with a strongly negative North Atlantic Oscillation contributing to conditions that enhanced melt during 2012. In this case, it appears that natural variability is beginning to be pushed by human-forced warming into a phase where certain years will preferentially further enhance Greenland melt. To this point, the tendency for large surface melt spikes was found to have increased during recent years. In contrast to Antarctica, where warming oceans contact glacial cliff faces and ice shelf undersides to accelerate melt, in Greenland, surface melt appears to currently be playing a bigger role in driving melt acceleration.
Surface melt can produce odd and unstable patterns of melt ponding and runoff over large ice sheets like Greenland. And as Greenland continues to warm due to human-forced climate change, an increasing risk of glacial outburst floods can be the result. The highly variable nature of surface melt is also a concern. In other words, overall warming can produce extreme, if brief, periods of warmth over Greenland that produce disproportionately large melt spikes. In this case, 2012 should not be seen as an outlier, but as the first of many future strong surface melt years — ones that will almost certainly surpass that year in melt intensity unless human-forced warming is somehow brought to a halt.
Hat tip to Colorado Bob