Greenland’s Contribution to Sea Level Rise Doubled During 2011-2014 — Larger Melt Pulses on the Horizon

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.

According to the study:

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 Loss from Greenland and Antarctica

(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.

Links/Attribution/Statements

A High Resolution Record of Greenland Mass Balance

Excellent Comment on the Paper By Slate writer Phil Plait

Charting Ice Sheet Contributions to Global Sea Level Rise

Glacial Outburst Flood

Hat tip to Colorado Bob

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Greenland’s Late August Rain Over Melt Ponds is a Glacial Outburst Flood Hazard

Glacial melt ponding on steep ice faces. Above freezing temperatures for an extended period. Storms delivering rainfall to the glacier surface.

These three events are a bad combination and one that, until recently, we’ve never seen before for Greenland. It is a set of circumstances directly arising from a human-driven warming of the great ice sheet. And it is one that risks a highly violent and energetic event in which melt ponds over-top and glaciers are flushed and ripped apart by surges of water rushing for scores of miles over and through the ice sheet. Major melt pulse events called glacier outburst floods that can result in catastrophically large volumes of water and broken ice chunks issuing from the towering, melting glaciers of Greenland and Antarctica.

It’s a risk we face now, as the circumstances driving the risk of such an event are present today.

Rain over Ice on August 21, 2014

Over the past four days a high amplitude wave in the Jet Stream and coordinate domes of high pressure over Greenland have delivered well above average temperatures for the great Northern Hemisphere ice sheet. Near and just to the east of the Jakobshavn glacier on the West Coast of Greenland, temperatures have ranged between 5 and 10 degrees Celsius above average.

Greenland Temperatures August 21Rain over Greenland Melt Ponds on August 21, 2014

(GFS temperature and rainfall analysis for Greenland on August 21, 2014. Note the above freezing temperatures and rainfall over the region of the Jacobshavn Glacier for today. Image source: University of Maine’s Climate Reanalyzer.)

What this means is a persistence of average temperatures in the range of 34-40 degrees (F) over large sections of Greenland’s Jakobshavn glacier. Melt level readings over a region that has now experienced ongoing surface ponding for more than 60 days.

But these warm temperatures, providing yet more heat forcing to melt the ice, aren’t the only extreme weather factor for the Jakobshavn glacier today. For today has brought with it a warm, wet over-riding airmass emerging from Baffin Bay and the Atlantic Ocean to the south. The warm air, coming into contact with the cooler glacier air is condensing and disgorging a series of rainstorms, dumping above-freezing water into the Jakobshavn’s already swelling pools.

Some of these effects are directly visible in the LANCE MODIS satellite imagery provided by NASA.

Glacial melt ponds are indicated in the satellite shot below by light-to-dark blue splotches on the glacier surface. Shallow surface melt ponding and pooling is indicated by a thin skein of light blue. In the left frame below, you can see the extensive and large melt ponds in the region of the Jakobshavn Glacier on August 18, 2014. For reference, the largest of these ponds are between 2 and 4 kilometers across. Also note the pale blue color of the ice near the larger ponds, indicating extensive smaller ponds in the region.

In the right frame, we have today’s LANCE-MODIS satellite shot. You will note that the entire frame is covered by cloud but that you can still see the blue undertone of the melting glacier below the rain-bearing clouds.

Melt Ponds, Jakobshavn August 18Rain over Melt Ponds

(LANCE MODIS satellite shot of the Jakobshavn Glacier on August 18 [left frame] and August 20 [right frame]. Note the widespread melt ponds and blue ice indicating smaller ponds over the glacier structure. Image source: LANCE MODIS.)

Assessing Glacial Outburst Flood Risk

Some day, as Greenland continues to warm under the human heat forcing and as more hot air invasions ride up over the ice sheet, a period of warmth followed by rainstorms may well set off a major outburst flood event. The water content in melt ponds over the glacier may well be far greater than what we see now and a series of over topping events, starting higher on the ice sheet and magnifying toward the ice sheet base, would set of a chain of events leading to such a flood.

Risks for this kind of event today may well be moderate to low. The glaciers at this point are craggy and much of the flood waters shunt through holes in the ice to water pockets or to the glacier base. But eventually, as the glacier contains more water through subsequent years of melt, flooding and damming will be more prevalent throughout the ice sheet. And so risks will likely be on the rise.

Other than similar events occurring in the Himilayas, we don’t really have much of a context by which to judge risk for large Greenland outburst flood events. We do know that melt ponding is now quite extensive in this region and we do know that the glacier itself is rather unstable — moving with rapid speed toward the ocean and containing pockets of melted water from past melt pond formation over the last two decades.

For today, I’m pointing out the current rainfall over ice and melt ponding event as part of a larger and dangerous trend, one that is likely to play a primary role in the pace and violence of Greenland melt going forward.

zodiac on greenland melt pond

(Photograph of a zodiac on the surface of one of Greenland’s very large melt ponds. Image source: Earth Observatory.)

Links:

University of Maine’s Climate Reanalyzer

LANCE MODIS

The Glacial Megaflood

Smokey Greenland Sees Another Summer of Substantial Melt

Smoke From Canadian Wildfires Near Greenland

(Smoke from Record Northwest Territory Wildfires on August 1, 2014 crossing Baffin Bay and the West Coast of Greenland. Image source: LANCE-MODIS.)

According to our best understanding of paleoclimate, at current greenhouse gas levels of 402 parts per million CO2 and 481 parts per million CO2e, the Greenland Ice Sheet eventually melts out entirely. It’s a level of atmospheric heat forcing we’ve already set in place, a level that keeps rising at a rate of about 2.2 parts per million CO2 and 3 parts per million CO2e each and every year due to our ongoing and reckless carbon emissions. And it’s a level that is already starting to receive substantial additions from destabilizing permafrost carbon together with likely increasing releases from sea bed methane stores.

In this, rather stark, geological, climatological and physical context, we ask the question — is it possible for us to stop a wholesale collapse of Greenland’s ice? And we wonder, how long can the ice sheet last as human greenhouse gas forcings together with ongoing releases from some of Earth’s largest carbon stores continue to rise?

Greenland Jacobshavn July 30 2014

(Extensive melt ponds, Dark Snow on West Face of Greenland Ice Sheet near the Jakobshavn Glacier on July 30, 2014. Extensive darkening of the ice sheet surface, especially near the ice sheet edge, is resulting in more solar energy being absorbed by the ice sheet. Recent studies have shown that edge melt results in rapid destabilization and speeds glacier flows due to the fact that edge ice traditionally acts like a wall holding the more central and denser ice pack back. Notably, the Jakobshavn is currently Greenland’s fastest glacier. Image source: LANCE-MODIS.)

For ultimately, our ability or inability to rapidly mitigate and then draw down extreme levels of atmospheric greenhouse gasses will provide an answer these key questions. And whether we realize it or not, we are already in a race against a growing Earth Systems response that may eventually overwhelm our efforts, if we continue to delay for too long.

But there’s a lot of inertia in the ice. It represents aeons and aeons of ancient cold locked in great, mountain-high blocks. And its eventual release, which is likely to continue to ramp higher and higher this century, is bound to result in a temporary and weather-wrecking outrush of that cold causing dramatic swings in temperature and climate states to be the rule of the day for Greenland as time moves forward.

Melt Ponds Zachariae Glacier July 25, 2014

(Large melt ponds, extensive surface water over Zachariae Glacier in Northeast Greenland on July 25 of 2014. For reference, the larger melt ponds in this image range from 1 to 4 kilometers at their widest points. The Zachariae Glacier sits atop a deep, below sea level channel that runs all the way to a massive below sea level basin at the center of the Greenland Ice Sheet. This Glacier is now one of more than 13 massive ice blocks that are moving at ever increasing velocity toward the ocean. Image source: LANCE-MODIS)

So we should not expect any melt to follow a neat or smooth trend, but to instead include large variations along an incline toward greater losses. In short, we’ve likely locked in centuries of great instability and variability during which the great ice sheets are softened up and eventually wither away.

Another Year of Strong Greenland Melt

In the context of the past two decades, the 2014 summer melt has trended well above the 30 year average in both melt extent and surface mass losses. Though somewhat behind melt during 2012, 2014 may rank in the top 10 melt years with continued strong melt in various regions and an overall substantial loss of ice mass.

Surface melt extent appears to be overall above 2013 values, ranging well above the 1981-2010 average, but significantly below extents seen during the record 2012 melt:

Greenland Melt Summer 2014Greenland melt 2013

Greenland Melt 2012

(Last three years of surface melt extent with the most current melt graph for the 2014 melt season at the top and the preceeding years 2013 and 2012 following chronologically. Dotted blue line indicates 1981-2010 average. Top three surface melt years in the record are 2012, 2010 and 2007, respectively. Image source: NSIDC.)

Overall, 2014 showed four melt spikes above 35% melt coverage with three spikes nearing the 40% melt extent coverage mark. By contrast, 2013 only showed two such melt spikes, though the later spike was slightly more intense than those seen during 2014. 2012’s 150 year melt, on the other hand, showed melt extents ranging above 40 percent from mid June to early August with two spikes above 60% and one spike above 80%.

Losses of mass at the surface also showed above average melt trends, but with net melt still below both 2013 and 2012:

Greenland Surface Mass Balance 2014

(Greenland surface mass balance trend for 2014 [blue line] compared to mean for 1990 to 2011 [gray line] and record melt year of 2012 [red line]. Image source: DMI.)

2012 was a strong record year and, on average, we’d expect to see the record jump back to lower levels after such a severe event. However, there’s little to indicate that either 2013 or 2014 have bucked the trend of ongoing and increasing surface melt over Greenland. To the contrary, that trend is now well established with yearly surface mass losses now taking place during all but one of the last 13 years. And there is every indication that 2014 will be a continuation of this trend.

Basal, Interior Melt Not Taken Into Account in the Surface Measure

While surface measures are a good measure of melt on the top of the ice sheet, it doesn’t give much of an idea of what’s happening below the first few feet. There, during recent years, sub surface melt lakes have been forming even as warming ocean waters have eaten away at the ice sheet’s base. And since more than 90% of human-caused warming ends up in the world’s oceans even as many of Greenland’s glaciers plunge hundreds of feet into these warming waters, one might expect an additional significant melt to be coming from the ocean-contacting ice faces.

We can see an indication of the severe combined impact of basal, interior and surface melt in the GRACE mass measurements of the Greenland Ice Sheet since 2002. A record that finds a precipitous and increasing rate of decline:

Greenland Cumulative Mass Loss Through Late 2013

(Greenland cumulative mass loss through mid 2013. Data provided by the GRACE satellite gravity sensor. Image source: NOAA.)

It is this ongoing overall mass loss that tells the ice sheet’s full tale. One that now includes an ever-increasing number of destabilized glaciers speeding more and more rapidly seaward.

Links:

LANCE-MODIS

NSIDC

DMI

NOAA

Nature: Human Warming Now Pushing Entire Greenland Ice Sheet Into the Ocean

Dark Snow

The Arctic Methane Monster Exhales

Large Methane Plumes Discovered on Laptev Continental Slope Boundary

 

 

 

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