A Flood of Warm Water the Size of 30 Amazon Rivers is Melting One of East Antarctica’s Largest Glaciers

If we’ve learned anything this year, it’s that few of Antarctica’s submerged coastal glaciers are safe from the warming ocean. Places that we once thought wouldn’t be vulnerable to melt for decades or centuries are now starting to feel the heat of rising water temperatures.

The heat comes in the form of great floods of warmer than normal waters running beneath the ocean surface and then eating away at the undersides of ice shelves and sea fronting glaciers. These floods are provided by the warmth forced into the world ocean by rising global greenhouse gas concentrations. And such invasions are happening around Antarctica’s perimeter with increasing frequency. But perhaps the most disturbing such event now ongoing is the present warm water flood running in from the Southern Ocean toward East Antarctica’s Totten Glacier.

calving-front-of-the-totten-glacier

(The melting edge of the Totten Glacier. Image source: Antarctica.gov.)

Totten is a truly gigantic glacier. By itself representing an ice mass equal to that contained in all of West Antarctica’s many glaciers. If large sections of Totten and the associated Aurora Basin were to melt, seas could rise by 12 feet or more. During recent years, researchers identified a great canyon running between 2,000 and 3,600 feet below sea level and stretching six miles wide as a weak point for Totten — whose glaciers sit in an enormous, below sea level rift within East Antarctica.

Researchers recently found that the floating ice shelf buttressing Totten was melting from below. As of 2015, they hadn’t identified a mechanism for this melt. But they had a pretty short suspect list. This year, a new study led by Dr. Stephen Rich Rintoul found that a river of warm water flowing at a rate of 220,000 cubic meters per second was flooding into the vulnerable canyon entrance to Totten’s weak underbelly. The researchers determined that this volume of warm water — equaling a flow rate more than 30 times that of the Amazon River — was enough to account for the observed ice shelf losses over recent years in the range of 60 to 80 billion tons per year.

totten-glacier-basin

(The Totten Glacier of East Antarctica contains about as much ice mass as all of West Antarctica. Its catchment basin is roughly the size of the U.S. Southeast. Much of it sits below sea level. And an ice shelf buttressing the glacier’s largest outlet in a 6 mile wide and 3,600 foot deep canyon is rapidly melting. Once this ice shelf breaks apart, ocean water will flood inland along a reverse slope and the Totten Glacier will increase its rate of movement toward the ocean — significantly speeding rates of global sea level rise. Image source: Australian Antarctic Division.)

The study authors found that:

…several lines of evidence support the conclusion that rapid basal melt of the [Totten Ice Shelf] is driven by the flux of warm [modified circumpolar deep water] into the cavity: the presence of warm water at the ice front, the existence of a deep trough providing access of this warm water to the cavity, direct measurements of mass and heat transport into the cavity, the signature of glacial meltwater in the outflow, and exchange rates inferred from the heat budget and satellite-derived basal melt rates.

Presently, because the ice shelf floats, this melt is not adding to global sea level rise. But the shelf acts like a cork that’s stopping the rest of Totten from flowing into the ocean. And when the ice shelf weakens enough, it will rift and break apart — leaving the massive glaciers behind it exposed to the inrush of warm waters and removing the last major barrier preventing them from bursting out.

Links:

Ocean Heat Drives Rapid Basal Melt of Totten Ice Shelf

Scientists Confirm that Warm Ocean Water is Melting one of East Antarctica’s Biggest Glaciers

One by One, the Flood Gates of Antarctica are Breaking Open

Tottering Totten and the Coming Multi-meter Sea Level Rise

Antarctica.gov

Hat tip to Robert in New Orleans

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Dr James Hansen — Human Warming Pushing Seas Toward Exponential Rise of Several Meters This Century

Continued high fossil fuel emissions this century are predicted to yield … nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. Statement from a new scientific study led by Dr James Hansen entitled Ice Melt, Sea Level Rise, and Superstorms.

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This week, Dr James Hansen and colleagues published one hell of a groundbreaking bit of scientific research. It’s a multi-disciplinary study incorporating the work of 19 top climate scientists, glaciologists, paleoclimatologists, and other Earth Systems researchers. Scientists from NASA, GEOMAR, JPL, and other top research agencies including recognized names like Dr Eric Rignot and Dr Makiko Sato all appear on the contributors list.

Global mean sea level change

(Rates of sea level rise since 1900 and associated with a 1.1 C jump in global temperatures have already shown a non-linear progression. Ice Melt, Sea Level Rise, and Superstorms attempts to pin down just how fast glacial melt rates will increase over the coming decades.)

The paper covers three topics related to the rapid accumulation of fossil fuel driven greenhouse gasses in the atmosphere and related rapid warming — Ice Melt, Sea Level Rise, and Superstorms. In other words, the paper looks into what will likely be the initiation of a Heinrich Event during the 21st Century so long as high levels of human greenhouse gas emissions continue.

A Heinrich Event for the 21st Century

For those not familiar with a Heinrich Event — it’s one of those disastrous climate change related incidents that you really don’t want to see emerge. One that drives rapid sea level rise, wrenching climate dislocations, and is likely also a trigger for regional and possibly hemispheric superstorms. Something that’s occurred numerous times in the geological past when the great Greenland and West Antarctic ice sheets warmed enough to disgorge armadas of ice bergs into the North Atlantic and/or Southern Ocean. The kind of thing that scientist Steve Pacala called a Climate Monster in the Closet. And Dr. James Hansen and colleagues’ new study is the first of its kind to scientifically explore the potential occurrence of just such a freak and dangerous event during the 21st Century.

Because the paper covers such a broad range of topics related to Heinrich Events, I’ve decided to write a two-blog post covering it. This post will focus on the ice melt and sea level rise issues. The superstorm-generating aspect of Heinrich Events — which Dr Hansen and colleagues found was capable of producing waves powerful enough to pluck 1,000 ton boulders from the sea floor and deposit them upon hillsides in the Bahamas 130 feet above sea level 115,000 years ago — is something we’ll cover in a second related post over the next few days.

Warm Ocean Waters Attacking Weak Glacial Underbellies

The chief driver of Heinrich Events is spiking rates of glacial melt issuing from the Greenland and West Antarctic ice sheets and related outflow of ice bergs and fresh water into the North Atlantic or the Southern Ocean. Hansen and colleagues’ paper builds on recent work by Eric Rignot and others who’ve found that the contact of warming ocean waters with the submerged sea faces of glacial cliffs and undersides of floating ice shelves is a primary driver for melt and ice berg release during periods of local and global temperature increase.

Heinrich Event Amplifying Feedbacks

(Illustration from Ice Melt, Sea Level Rise, and Superstorms shows how ocean stratification acts as an amplifying feedback to glacial melt. Cool, fresh surface waters generated by the initial ice release set up a kind of ocean heat conveyor belt that delivers more and more warm water to the submerged underbellies of the great ice sheets. In Greenland, prograde beds limit the amount of ice that can be released in sudden events. In Antarctica, retrograde beds below sea level set up a situation where the amplifying melt feedback is further enhanced.)

Grounding glaciers and ice shelves are, at first, weakened by slow but ramping melt rates. Eventually, the glaciers and shelves collapse due to the weakening process of melt which leads to a surge of previously buttressed ice sliding out into the oceans. As more fresh melt water expands over the ocean surface, it traps heat into deeper layers of the water column near the submerged glacial faces. So initial melt produces an amplifying feedback that delivers more ocean heat to the ice and, in turn, results in more ice rushing out into the North Atlantic or the Southern Ocean.

Exponential Rates of Glacial Melt and Sea Level Rise

It is this mechanism that Hansen and colleagues fear will come into play over the course of the 21st Century. Their paper identifies a risk that such a mechanism could set up 5, 10, or 20 year melt doubling times for Greenland, West Antarctica or both this Century. A new perspective from some of the world’s top scientists that assumes the risk of non linear melt is high enough to present a major concern. As an example, under a 10 year doubling time, the current approximate 3 mm per year sea level rise would double to 6 mm per year by 2026, 12 mm per year by 2036, 2.4 cm per year by 2046, and nearly 5 cm per year by 2056.

Doubling times in non linear events often don’t fit a pure exponential curve — instead tending to follow a series of spikes and recessions with major transitional events coming at the end of any ‘curve.’ But Hansen’s particular perspective is useful given the fact that current rates of sea level rise do not appear to be following a linear pattern and due to the fact that the mechanism for large, Heinrich Event type glacial melt spikes is becoming more supported in the observational science.

Rate of Greenland Antarctica Mass Change

(It’s still early days for Greenland and Antarctic melt. However, current trend lines do point toward a potential for multi-meter sea level rise this Century. Image source: Ice Melt, Sea Level Rise, and Superstorms.)

Early measures of Greenland and Antarctica ice mass loss imply 8-19 year melt doubling times for Greenland and 5-10 year melt doubling times for Antarctica. For reference, if both these ice systems continued to double mass loss on a roughly 10 year basis, total sea level rise by the 2090s would equal 5 meters or 16.4 feet. By contrast, a 5 year doubling time would result in 5 meters of sea level rise by the late 2050s and a 20 year doubling time would result in nearly a meter of sea level rise by the end of this Century and 5 meters worth of sea level rise by 2160.

Hansen notes that these are still early days and it is unlikely that ice sheet response trends have become clear at this stage. However, initial trend lines, though likely to be less accurate, appear to pose some cause for concern. In addition, Hansen points out that rates of sea level rise are less likely to be constrained by ice sheet inertia during periods when global temperatures are rapidly rising. Projected rates of global temperature increase in the range of 1-5 C this Century is on the order 20-100 times faster than during the end of the last ice age — at the upper end covering all of the 10,000 years worth of ice age warming in just one Century. And Hansen notes that this potentially extreme rate of temperature increase poses a much greater risk of rapid glacial destabilization than is indicated by current IPCC glacial melt models.

Hansen’s research also points to the likelihood that rapid glacial melt would temporarily put a break on rates of global atmospheric warming by cooling local ocean surfaces and increasing the rate of heat transfer into middle ocean layers. And it’s this energy flip-flop and related heightened imbalance that provides a pretty severe potential storm set-up as rates of glacial melt ramp up.

Links:

Ice Melt, Sea Level Rise, and Superstorms

Climate Guru James Hansen Warns of Much Worse Than Expected Sea Level Rise

Dr James Hansen

Dr Eric Rignot

Dr Makiko Sato

Heinrich Event

Climate Monsters We Want to Keep in the Closet

Melting in West Antarctica Could Raise Seas By 3 Meters

Hat Tip to DT Lange

Hat Tip to Colorado Bob

Hat Tip to TodaysGuestIs

Human-Baked Baffin Bay Takes Biggest Bite Yet out of The Greenland Ice Sheet

You wouldn’t generally think of ocean temperatures in the range of 40 to 50 degrees Fahrenheit (5 to 10 degrees Celsius) as hot. But to the great sea-fronting glaciers of Greenland it may as well be boiling.

Greenland Ice Sheet in Hot Water

All it takes is 32 degree F (0 C) water to begin melting the ice. And for each 1 degree increase above that margin, melt rates will dramatically ramp higher. Though a typical summer will push ice to melt at the Greenland seafront ice edge, this year, especially near Baffin Bay, the melt pressure has been extraordinary.

Ever since late June, 40-50 degree F sea surface temperatures have dominated the ice edge zone. For most regions that’s temperatures in the range of 4-11 degrees Fahrenheit (2-6 C) above average. The kind of heat that really risks a rapid melt along the ice margin.

Above Normal Sea Surface Temperatures Near Greenland

(Sunday, August 16 sea surface temperature anomalies as provided by NOAA.)

A latent heat that sits at the surface, gnawing away at the ice, waiting for a fresh water flood. And when the fresh water does come, that hotter, saltier, heavier water is forced downward beneath the lighter fresh water outflow. At this point, the hotter waters are locked below the surface where they go to work eating away at the glacier base. Notably, the only region within Baffin Bay where we currently see cooler surface water is in the major glacier melt zone near Jakobshavn. It’s an indication that ice melt from a major glacier outflow there is cooling the surface waters even as it pulls the surface heat downward and toward the glacial base.

This glacial melt heat conveyor is the kind of process we are seeing more and more frequently near the great ice sheets as fossil fuel industry has continued its harmful emissions. And, it’s a process that, this week took a huge chunk out of one of the world’s fastest moving ice masses.

Huge Chunk of Jakobshavn Breaks Off

According to reports from The Arctic Ice Blog, the Jakobshavn glacier sent its biggest chunk of ice on record floating off into Baffin on August 16 of 2015. For a glacier that drains 6.5 percent of the Greenland Ice Sheet and that has been known to release icebergs the size of Lower Manhattan, that’s really saying something.

You can see this amazing and rather chilling calving event in action in the August 14 to August 16 satellite imagery comparison developed by Espen Olsen below:

Espen Jakobshavn

(Jakobshavn experiences what is likely it’s largest calving event yet on Sunday, August 16, 2015. Image source: Espen Olson.)

Here we see the ice-choked Baffin Bay waters rapidly surging inland and taking up more of the Jakobshavn’s traditional outflow channel. What we do not see in this image, but what clearly happened, was that an ice mass hundreds of meters tall and covering an area of about 12.5 square kilometers was shattered into flinders as warming ocean waters invaded the Greenland Ice Sheet. Waters that will deliver still more heat to the ice. Waters that seek for the very heart of Greenland — a below sea level basin topped with 2-3 kilometer tall mountains of ice.

Back in the 19th Century, the Jakobshavn Fjord was half full of grounded Greenland ice. A long tongue of the glacier extended on outward through the channel. As of 2015, the Fjord is now completely full of water and ocean-bound ice bergs. The ocean itself has begun to invade the much larger ice masses beyond the Fjord. The broader inland mass of the Jakobshavn Glacier which is now directly in contact with the rising seas (indicated as Jakobshavn Isbrae on the maps above and below).

Jakobshavn Melt Progression

(Warming waters from Baffin Bay have driven through the ice in the Jakobshavn Fjord and are now boring into the thicker ice masses of Jakobshavn Ibrae. An impact that has serious implications for global sea level rise. Image source: The Arctic Sea Ice Blog and Espen Olsen.)

The inland-retreating Isbrae itself is a vast field of giant ice sheets. Massive tilting escarpments of luminous ice that, in the current age of fossil fuel forced warming, often cup great 1-3 kilometer long melt ponds in their wildly varied topography. It’s a single region that, in total, may hold about 1.5 feet of global sea level rise locked away in a rapidly melting ice pack. And Jakobshavn is just one of many regions (together containing about 15-20 feet worth of sea level rise) that are currently undergoing rapid melt due to the invasions of warming ocean waters.

Links:

NOAA

The Arctic Ice Blog

Espen Olson

A-Team

LANCE-MODIS

The Human-Warmed Southern Ocean Threatens Major Melt For East Antarctica

Totten Glacier. A mountainous expanse of ice in the very heart of the greatest accumulation of frozen water on Earth. A bastion of cold containing 11.5 feet worth of sea level rise if it were to melt in total. An accumulation roughly equal to half of all the frozen water in the whole of the Greenland Ice Sheet.

According to a new scientific report out this week, Totten Glacier is under threat of melt. Warm water is swelling up through troughs in the Continental Shelf zone, approaching the ice shelf locking Totten and a vast swath of interior East Antarctic glaciers. As with West Antarctica, this warm water upwelling has the potential to rapidly destabilize an already fast-moving glacier.

Totten Glacier basin

(Totten glacier outflow zone covers a massive region of East Antarctica. An area about equivalent in size to the entire US Southeast region. Warm water is starting to encroach upon an ice shelf locking this great ice mass into its Continental Catchment Basin. Image source: Australian Antarctic Division.)

Totten already hosts one of the most rapid thinning rates in East Antarctica. And, in fact, it was a satellite detection of this very thinning that set off a recent scientific investigation of the glacier’s stability. What the new scientific report identified was a threat that enhanced warm water upwelling from a human-heated circumpolar current would collide with an ice structure that is already vulnerable to melt.

The net result would mean a destabilization and acceleration of one of the greatest ice masses on the planet. Such an event would have far-reaching implications, especially relating to the pace and end state of warming-related global sea level rise.

From the abstract of Ocean Access to A Cavity Beneath Totten Glacier:

Totten Glacier… has the largest thinning rate in East Antarctica. Thinning may be driven by enhanced basal meltingWarm modified Circumpolar Deep Water, which has been linked to glacier retreat in West Antarctica, has been observed in summer and winter on the nearby continental shelf beneath 400 to 500 m of cool Antarctic Surface Water…We identify entrances to the ice-shelf cavity below depths of 400 to 500 m that could allow intrusions of warm water if the vertical structure of inflow is similar to nearby observations. Radar sounding reveals a previously unknown inland trough that connects the main ice-shelf cavity to the ocean. If thinning trends continue, a larger water body over the trough could potentially allow more warm water into the cavity, which may, eventually, lead to destabilization of the low-lying region between Totten Glacier and the similarly deep glacier flowing into the Reynolds Trough. (emphasis added)

At issue are two pathways for this upwelling, warm, deep water to follow:

totten_glacier_labeledpaths

(Topographic map of the Totten Glacier outlet region and nearby seabed. Note the vulnerable water inlets [orange lines], the inland troughs and basins [red highlights and blue topographic signature] and the rather advanced inland extent of the grounding line [white line]. Image source: Ocean Access to a Cavity Beneath Totten Glacier.)

The pathways are identified by the orange lines in the topographic image above. The lines identify underwater valleys that run out to the deeper, warmer waters accumulating on the edge of the Antarctic Continental Shelf region. As the waters rise, scientists are concerned that these troughs will act like channels, funneling a flood of much warmer than normal water beneath the belly of the great glacier.

The result is an instance of ‘global consequence.’ The authors note:

We estimate that at least 3.5 m of eustatic sea level potential drains through Totten Glacier, so coastal processes in this area could have global consequences.

Indeed. If we add in all the other destabilized glaciers around the world to Totten, should it destabilize, you end up with about 26 feet of sea level rise locked in. And that has some pretty staggering consequences when you look at impacts to the world’s coastlines.

This is what 20 feet of sea level rise impact looks like for the US Southeast and Gulf Coasts:

NASA six meter sea level rise SE

(Six meters of sea level rise would permanently inundate many of the major cities along the US Gulf and Southeastern coasts. Areas inundated shown in red. Image source: NASA.)

But, perhaps worst of all, is the fact that some of the world’s longest lasting and most stable accumulations of frozen water are now under threat of melt.

In essence, what we are witnessing is possible initiation of the end of the greatest and oldest ice province on Earth. East Antarctica glaciated 35 million years ago, when atmospheric CO2 levels fell below a range of 500-600 parts per million, and has been mostly stable or growing ever since. Now that region of ice, the most ancient remaining in the memory of Earth, is under threat. With human greenhouse gasses in the range of 484 ppm CO2e (CO2 equivalent) and 400 ppm CO2 and rising, it appears that even the oldest glaciers are under existential threat.

To this point, Eric Rignot noted in a recent interview:

“..the stage is set. You have a submarine glacier and a deep trough. The warm water is not too far from that frontal region and we’ve seen some changes in the glaciers that suggest that something is happening at their base.”

Links:

Ocean Access to A Cavity Beneath Totten Glacier

Hidden Channels Beneath East Antarctica Could Cause Massive Melt

Australian Antarctic Division

NASA

A Glacier Area the Size of the Entire South is Melting Away

Arctic Sea Ice Flirts With New Record Lows Dragging Global Coverage Inexorably Down

It’s another winter of far above average temperatures for the Arctic.

Warm air has risen — south to north — over both the North Atlantic and Pacific. It has ridden through the Bering and Barents seas. And it has invaded an Arctic sea ice pack that is far, far more fragile than it has ever been in modern human reckoning.

image

(A parade of warm fronts predicted to run up through the North Atlantic and Barents between Greenland and Northern Europe and on up into the Arctic Ocean on Thursday, March 5. The warm fronts are indicated by regions of perpendicular wind flow across the meridional pattern running northward from the Eastern Seaboard of North America and on into the Arctic. It is a pattern we’ve seen frequently throughout the winter of 2014-2015. One that has resulted both in Arctic warming and extreme polar vortex excursions. Image source: Earth Nullschool. Data Source: Global Forecast Systems Model.)

The winds have been fed by the warmest ocean surface temperatures ever seen in the aftermath of the hottest year on record (2014). They have pushed against ice packs off Irkutsk in Russia. They have driven ice northward and melted it throughout the Bering. And they have pushed 10-20 foot waves against the ice along the coasts of Greenland, in the Strait near Svalbard, and in the Barents west of Novaya Zemlya.

Near Record Low Arctic Sea Ice

This warm air influx has had a strong effect on the sea ice. Even in the far north near the pole, sea ice has been occasionally observed to thin this winter, reaching 80-90 percent concentration in a broad patch just south of the pole. Marked thinning for an area from which thicker, multi-year ice has undergone an extended retreat and 2 meter thick ice is now the mainstay. A mere shadow of ice for a region that once featured great hills and mounds of stable ice bounded by bridges between the North American and Asian Continents.

Now, over the greatly thinned and reduced ice, periods when temperatures have neared or even exceeded the point at which sea ice melts (28 F) have become more and more common in a broad wedge covering the Arctic Ocean between Novaya and the pole itself. When combined with the warm waters continuing to invade the Arctic Ocean from the flanks and from below, it’s enough to have again pushed sea ice to near record low extents for this time of year:

chart

(Arctic sea ice extent for March 1 of 2015 shown by the purple line sandwiched between the orange line [2011] and the pink line [2006]. Yesterday’s sea ice extent was second lowest in the record with 2006 being the lowest and 2011 running in as third lowest for the date. 2012 [dotted green], 2007 [light blue] and 1979 [dark blue] were added for reference. Image source: NSIDC.)

At the current measure of 14,450,000 square kilometers, that’s well less than what we’ve seen during previous decades. More than 2,000,000 square kilometers, or about an area the size of Greenland, less than 1979’s extent for March 1, for example.

And the total could well go lower — testing new record ranges for early March. For the Arctic is about to see another major influx of warm air.

Starting tomorrow and through Saturday, warm southerly winds will ride up into both the Bering and through the Barents side of the Arctic Ocean east of Novaya Zemlya. The warm air influx will be strongest through the Barents region, pushing temperatures as warm as 30 F to withing 200 miles of the North Pole:

image image

(Forecast for Wednesday finds 30 F temperatures riding up through the Barents and deep into the Arctic Ocean to within 200 miles of the North Pole. Note that similar temperatures appear in Ohio on the same day in the second frame. Image source: Earth Nullschool. Data source: Global Forecast Systems Model.)

For comparison Ohio, many hundreds of miles to the south and well outside the Arctic, will see the same reading at the same time. It’s another major warm air influx that will again drive against the ice pack. A continuation of a decades long assault that will bring with it further threat of record lows in Arctic sea ice. One that could set the 2015 melt season up for a rather low launching pad if the major gains seen during this time of year in 2012, 2013, and 2014 don’t manage to materialize.

NASA Study Finds 35,000 Square Kilometers of Sea Ice Lost Each Year Globally

As Arctic sea ice faces the potential for new all-time lows, a recently released NASA study puts these losses in a global context.

This important broader assessment shows that both Arctic sea ice loss and global sea ice loss since 1979 has followed an unequivocal trend of thinning and recession. This ongoing loss is despite the fact that Antarctica has seen some minor gains in sea ice extent during that same period.

Claire Parkinson, author of the study, noted:

“Even though Antarctic sea ice reached a new record maximum this past September, global sea ice is still decreasing. That’s because the decreases in Arctic sea ice far exceed the increases in Antarctic sea ice.”

A graphic illustration of sea ice trends shows how rates of global and Arctic decline compare when adding in the slight and far more gradual sea ice gains occurring near Antarctica:

polar_trend_graphs_1979-2013

(NASA Polar Trend Graph shows Arctic, Antarctic, and combined global sea ice trends. Note the slight gain for Antarctica as compared to a precipitous fall for the Arctic even as the global trend shows a marked downswing. Image source: NASA.)

Massive losses in the Arctic are likely due to the fact that the sea ice there sits upon a warming ocean surrounded by warming continents. By contrast, Antarctic sea ice sits in the Southern Ocean whose surface waters are often cooled both by winds and by an increasing outflow of cold, fresh water from the melting Antarctic glaciers. Factors that serve as a minor surface counter-trend to the larger warming signal. A signal, that for Antarctica, is driving an assault of warm water at the ice sheets from the depth of hundreds of feet below the ocean surface.

Overall, the Arctic has lost of an average of 2 million square kilometers since 1979. Antarctic gains of about 700,000 square kilometers are enough to result in a global loss of around 1.3 million square kilometers over the period. That’s equal to about 35,000 square kilometers lost each year or an area the size of the State of Maryland.

Finally, it’s important to note that recent studies have shown (as hinted at above) that sea ice gain around Antarctica is being driven by cold water and ice berg outflows ramping up as the great glaciers of Antarctica increase their melt rates. The melt, which is driven by a pool of warm water expanding hundreds of feet beneath the ocean surface and at the base of ice sheets and ice shelves is creating a kind of heat conveyor which spreads cool water along the surface even as it pulls more warm water in from underneath.

So it appears even the slight ice gain for Antarctica has a connection to human caused warming. One that is even more ominously linked to an exponentially ramping rate of land ice loss from Antarctica itself.

Links:

NSIDC

NASA: Global Sea Ice Diminishing, Despite Antarctic Gains

Earth Nullschool

Global Forecast Systems Model

Expanding Arctic Sea Ice is Flooding Warning Bell

Cryosat Shows Rate of Antarctic Land Ice Loss Doubled During Last Decade

Hat Tips:

The Arctic Sea Ice Blog

Anna

Dnem

New Study Finds 3-4 Meter Sea Level Rise From Antarctica May be Imminent

Ocean stratification. A condition characterized by the separation of layers of water of different temperatures and chemical make-up. A condition that has serious impacts to the geophysical nature of the worlds oceans, to the ability of oceans to support life, and to the stability of the vast glaciers of Antarctica — whose faces plunge as deep as hundreds of feet into the Southern Ocean.

In the Antarctic, today, what we see is a cold surface layer and a heating bottom layer. The cold surface layer is fed by an expanding pulse of chill, fresh water issuing from the melting glaciers of Antarctica. Over the years it has become more uniform, sequestering cold near the surface as warmth builds up in the depths below. The deeper hot layer is fed by warmer water issuing in from the tropics and heated to temperatures not seen for tens of thousands of years. This hot water bears a heavy burden of salt. So it is denser and it dives beneath the expanding fresh water layer. The insulating fresh, cold water layer prevents mixing between the bottom layer and the surface. Such mixing would cool the bottom layer. But instead the heat builds and builds and builds.

Difference in Ice mass Between now and last glacial maximum

(Antarctica — visual difference in ice mass between now [right] and last glacial maximum [left]. By mid century, atmospheric greenhouse gas concentrations driven by humans could be high enough [550 ppm CO2e+] to melt all the remaining ice upon this now-frozen continent. Image source: NASA/Goddard Space Flight Center.)

Ocean currents bring the deep, hot water in contact with the base of Antarctica’s massive glaciers. And this intensely focused heat engine goes to work to rapidly melt the ice.

It is this condition of ongoing and intense melting of the ice sheet’s bases that terminate in faces of ice cliffs, hundreds of feet high and deeply submerged in the sea, that is driving the irreversible collapse of many glaciers in Antarctica. Already, due to this irreversible fall, the entire flank of West Antarctica is under collapse — locking in at least three feet of sea level rise from this region alone going forward.

But now, a new study finds that these conditions — the same conditions we observe today — led to the release of enough glacial ice from Antarctica alone at the end of the last ice age to raise sea levels by 3-4 meters (10-13 feet) in just 1-3 centuries.

From Nature Communications:

“The reason for the layering is that global warming in parts of Antarctica is causing land-based ice to melt, adding massive amounts of freshwater to the ocean surface,” said ARC Centre of Excellence for Climate System Science researcher Prof Matthew England an author of the paper.

“At the same time as the surface is cooling, the deeper ocean is warming, which has already accelerated the decline of glaciers on Pine Island and Totten. It appears global warming is replicating conditions that, in the past, triggered significant shifts in the stability of the Antarctic ice sheet.”

The last time this happened was 14,000 years ago as the Earth slowly warmed out of the end of the last ice age. But the result was anything but gradual:

“Our model simulations provide a new mechanism that reconciles geological evidence of past global sea level rise,” said researcher UNSW ARC Future Fellow Dr Chris Fogwill.

“The results demonstrate that while Antarctic ice sheets are remote, they may play a far bigger role in driving past and importantly future sea level rise than we previously suspected.”

“The big question is whether the ice sheet will react to these changing ocean conditions as rapidly as it did 14,000 years ago,” said lead author Dr Nick Golledge, a senior research fellow at Victoria’s Antarctic Research Centre.

These are critical questions. Ones that have serious impacts for the more than 700 million people now living within 10 meters of current sea level.

Antarctic Ice Shelf Thickness Changes

(Antarctic Ice Shelf thickness changes. Note the thinning of almost all the ice shelves along the margin of Antarctica. Ice shelves anchor interior ice, keeping it from rushing out through deep channels into the Southern Ocean. Rapidly thinning ice shelves is a precursor to glaciers rushing toward the sea. Image source: Nature Pritchard et al. 2012)

To this point it is worth noting that the pace of warming 14,000 years ago was on the order of 0.05 degrees Celsius each century. The current pace of human-driven warming over the past century was 20 times faster. This century, the warming is predicted to be as much as 500 times faster (3-5 C warming by 2100). So the question may we be — will Antarctica respond as ‘slowly’ as it did at the end of the last ice age? Slow as in ice outbursts that lead to sea levels rising by as much as 14 feet during one century.

Links:

Change Antarctic Conditions Could Trigger Steep Rise in Sea Levels

Antarctic Contribution to Meltwater Pulse 1A From Reduced Southern Ocean Overturning

Weighing Change in Antarctica

It’s All About Fresh Water — Rapid Sea Level Rise Points to Glacial Melt in Antarctica

Human-Destabilized Antarctica Capable of Glacial Outbursts Contributing to Sea Level Rise of 14+ Feet Per Century

Antarctic Ice Sheet Loss Driven by Basal Melting of Ice Shelves

(Hat Tip to Colorado Bob)

 

 

 

 

 

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

Grim News From NASA: West Antarctica’s Entire Flank Collapsing Toward Southern Ocean, At Least 15 Feet of Sea Level Rise Already Locked-in Worldwide

(Must-watch NASA presentation finding six Antarctic Glaciers in irreversible collapse.)

Human-caused heat forcing. From the top of the atmosphere to the bottom of the world’s oceans, there’s no safe place to put it. For where-ever it goes it sets in place conditions with the potential to unleash gargantuan forces.

481. Minus aerosols, that’s the equivalent CO2 heat forcing humans have now built up in the atmosphere due to a constant and rapidly rising greenhouse gas emission. By itself, this heat forcing, were it to remain in the world’s atmosphere and ocean system, is enough to melt all of West Antarctica, all of Greenland, and part of East Antarctica pushing sea levels higher by between 30 and 120 feet or more.

Inertia. Namely, the massive inertia in the Earth climate system creating a perceived ability to resist rapid destabilization due to the human insult. It’s the one hope scientists and policy-makers alike pinned on the possibility of bringing human greenhouse gas emissions down in time to prevent radical and damaging change.

Rapid glacier and ice sheet destabilization. What, by 2014, became understood as the new reality, as an ever-increasing number of the world’s glaciers displayed far less resilience than previously anticipated and were set in motion to an unstoppable and catastrophic reunion with the world’s oceans by human warming.

Now, a new NASA study finds that six of West Antarctica’s largest glaciers are in a state of irreversible collapse. These add to a growing tally of destabilized glaciers from Greenland to Svalbard to Baffin Island to Antarctica and beyond which, all together, show that at least a 15 foot sea level rise from human-spurred glacial release is now inevitable.

Their names were Pine Island, Thwaites, Haynes, Pope, Smith and Kohler

antarctica_screen_grab1_2

(The locations of West Antarctica’s ‘butcher board’ glaciers — those that are doomed to an inevitable embrace with the Amundsen Sea. Image source: NASA.)

At issue are six massive glaciers representing more than 1/3 of total the ice mass of West Antarctica and what could well be called its entire weak flank.

As early as 1968, this massive section of West Antarctica was listed as unstable. Since that time, human heat forcing has pumped higher and higher volumes of warmth deep into the Pacific Ocean. The warmth pooled in the depths, building, even as it rose up beneath Antarctica. Ocean circulation and Ekman pumping along the coast of Antarctica brought this warm water up from the depths where it traveled along the continental shelf zone to encounter Antarctica’s mile-high glaciers. The warm water did its work, unseen, for a time. Eating away at the bottoms of these glaciers and speeding their slide to the sea. The increased glacial melt and related fresh water outflow put a kind of cold water cap on the Southern Ocean around Antarctica. This cold cap gave the ever-warming bottom waters no outlet to the surface and so the heat concentrated where it was needed least — at the bases of massive ocean-fronting glaciers.

One section of West Antarctica, composed of the six glaciers now listed as undergoing irreversible collapse, was particularly vulnerable to this basalt melt and ocean upwelling heat forcing. For the glaciers there rested on a section of continental shelf well below sea level — extending scores of miles beneath the ice and on into interior Antarctica. As a result, newly undercut glaciers are flooded until they float, creating lift, reducing friction and rapidly speeding the glacier’s plunge seaward. Even worse, few sub-glacier ridges — speed bumps that glaciologists call grounding points — interrupt the more rapid flow of these glaciers once initiated.

(NASA slide-show illustrating the process of basal melt and grounding line retreat)

By earlier this year, a separate NASA study found that the Pine Island Glacier (PIG), one of the world’s largest glaciers and the most vulnerable ice sheet in West Antarctica, had entered a state of irreversible collapse. Now, the most recent study, led by glaciologist Eric Rignot at NASA’s Jet Propulsion Laboratory, finds that five of its fellows — Thwaites, Haynes, Pope, Smith, and Kohler — are following PIG’s lead.

Rignot’s findings could not be more stark:

“The collapse of this sector of West Antarctica appears to be unstoppable. The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers. At this point, the end of this sector appears to be inevitable.”

In other words, over the course of decades-to-centuries, these glaciers will disintegrate and slide into the sea until they are no more. Years from now, their names will be a distant memory, reminders of a faded and far better time.

At Least 15 Feet of Sea Level Rise From Glacial Melt Now Locked-in

This year, the pace of new announcements for massive glaciers undergoing destabilization or irreversible collapse could best be described as terrifying and unprecedented. And each new announcement brings with it starker implications for both the ultimate pace and scope of global sea level rise.

Global sea level rise

(Current pace of global sea level rise at 3.26 mm per year is likely now set to rapidly accelerate coincident with the rapid acceleration and melt of an ever-increasing number of the world’s glaciers. Image source: AVISO.)

The amount of sea level rise to result from just the loss of the disintegrating section of West Antarctica described in the most recent NASA study amounts to at least four feet. But looking around the world we also find rapid destabilization of more than 13 glaciers encircling all of Greenland with one, the Zacharie Glacier, featuring an ice flow that stretches all the way to the center of the Greenland ice mass. Recent studies also find that the massive glaciers of Baffin Island and the world’s largest ice cap — the Austfonna glacier on Svalbard’s island of Nordaustlandet — are all locked in an inevitable seaward rush.

The total water composed in the moving and destabilized glaciers worldwide is now at least enough to raise world ocean levels by a total of 15 feet. But the inevitable loss of these glaciers tells a darker tale, one that hints that the 23 feet worth of sea level rise in all of Greenland’s ice and the 11-13 feet of sea level rise in all of West Antarctica’s ice may well be locked in to what is a growing daisy chain of explosive destabilization if human greenhouse gas levels aren’t radically drawn down.

In continuing to emit greenhouse gasses, we make the situation ever worse by imposing a heightening heat pressure on glacial systems that will both speed their release and ensure that an ever growing portion of the Earth’s ice ultimately melts. The current forcing though both extreme and dangerous is small compared to the potential forcing should we not rapidly reign in the human emission.

Links:

Must-Read NASA Study Showing Six of West Antarctica’s Glaciers in Irreversible Collapse

NASA Video: Antarctic Collapse Explained

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

Constant Arctic Heatwave Sends World’s Largest Ice Cap Hurtling Seaward

Doomed Pine Island Glacier Releases Guam-Sized Iceberg into Southern Ocean

Scientists: Warming Ocean, Upwelling to Make an End to Antarctica’s Vast Pine Island Glacier

NASA/UC Study: Warming Ocean Found to Melt Ice Sheets From Below

A Faustian Bargain on the Short Road to Hell: Living in a World at 480 CO2e

Hat tip to Peter Sinclair and Colorado Bob

 

Scientists: Warming Ocean, Upwelling to Make an End to Antarctica’s Vast Pine Island Glacier

Southern Ocean Interface With Pine Island Glacier

(Southern Ocean interface with Pine Island Glacier as seen during the second week of January, 2014. Note the ocean has already invaded substantially land-ward pushing the glacial coastline back by between seven and ten miles. Image source: Lance-Modis)

Among Antarctica’s most vulnerable ice shelves, the Pine Island Glacier (PIG) is a massive feature. It rests on sloped terrain that is mostly below sea level even as it spills out into the southern ocean through a nearby bay, calving great icebergs that then slowly ride out, like floating ice faerie castles, into the stormy seas. In total, the shelf covers 160,000 square miles, an area two thirds the size of Great Britain.

The Pine Island Glacier is vulnerable for many reasons. It rests on sloped land that tilts it toward the warming seas. Much of it rests below sea level, making its underbelly open to the assaults of the upwelling currents of a rapidly warming ocean. As portions of the under-structure melt, the glacier becomes buoyant, floating on surface waters subject to waves, winds and currents which adds further stress to inland structures.

A few anchors held the great glacier in place over the millenia. The great pressure of ice pushing down shoved the glacier deep into the underlying Earth, for the most part, sticking it in place as it only slowly ground toward the sea.

But now these anchoring features are disintegrating, the warming waters rushing in from underneath, lubricating the ice bottom. The slope, the gravity, the long tongues of ice entering the ocean are all coming into play. The great ice sheet is in motion. A motion that scientists now conclude will not stop until the entire glacier collapses into the heating waters.

Rumors of Glacial Demise

That the Pine Island Glacier was one of Antarctica’s most sensitive to human warming has long been well known to scientists. The geographic features surrounding the glacier, the relatively high angle of slope tipping the glacier toward the ocean, and the large section of the ice shelf below sea level all attracted interest, questions and research.

By the mid 1990s, records of massive melt coming from the Pine Island Glacier began, with upwards of 10 cubic kilometers of ice observed to be lost each year. With ice loss rates continuing to increase, more efforts focused on determining the glacier’s ultimate fate. By the mid to late 2000s, average net ice loss rates were over 20 cubic kilometers per year.

Calving Pine Island

(The July 2013 calving of the Pine Island Glacier as shown in a Lance-Modis satellite shot.)

At about the same time, in 2001, 2007, and 2013, three great icebergs calved off of Pine Island. These were massive bergs, averaging over 2000 square kilometers in size. Though large iceberg calving from the Pine Island Glacier was historically typical, the size and frequency of these amazing events were enough to raise eyebrows and add to already rampant speculation that the Glacier may well be headed toward an inexorable collapse.

Ocean’s Impact on Basal Melt Discovered

By 2010, studies were beginning to come in showing that the Pine Island Glacier was experiencing a rapid melt from underneath. Warming deep ocean currents were upwelling from the Amundsen Sea to erode the glacier’s base. Ice loss from this basal melt was estimated to be even greater than that observed through the increasingly rapid motion of the glacier and related large ocean calving events.

PIG basal melt

(Image source: Nature)

Basal melt was also shown to be undermining the glacier, pushing deeper and deeper beneath the ice shelf and driving ocean water further into the continent. The mechanism for this increased basal melt came directly from a human warming of the deep ocean surrounding Antarctica. Accelerated deep ocean warming was coming more and more into play as human atmospheric heating transferred through the ocean surface and into the depths.

In the Antarctic, a massive pool of warm water developed in the depths surrounding the continent. The warmer water gathered beneath a fresher, colder layer that kept a lid on the warmth, forcing it toward the bottom. But near the continents, the dynamics of ocean currents and coastal mixing brought this warm water up to contact the coast and, in this case, the base of the Pine Island Glacier.

A Nature Geoscience study led by Dr. Adrian Jenkins found progressive basal melt due to the action and heat transfer of this warm, upwelling water (see image above). The evidence collected seemed grim. It appeared that the Pine Island Glacier may well be in the first stages of disintegration. But more comprehensive study was needed before conclusions could be drawn.

Prognosis: Irreversible Collapse

By 2013, enough information had been collected to start making model runs to determine the ice sheet’s ultimate fate. And, recently, three teams of scientists took up the task. The results of these model runs were stark. They showed that, no matter what, Pine Island’s Glacier was probably suffering from the early stages of an irreversible collapse.

Antarctica glacial velocity map

(Glacial velocity map of Antarctica. Note the very high velocity of the Pine Island and adjacent Thwaites glaciers. Image source: Antarctic Glaciers)

In the new Nature study entitled “Retreat of Pine Island Glacier Controlled by Marine Ice Sheet Instability” the authors applying these models found that the glacier had “been kicked and it’s just going to keep on rolling for the foreseeable future.”

Dr Hilmar Gudmundsson, one of the study’s authors in a recent interview with BBC noted:

“Even if you were to reduce melt rates, you would not stop the retreat. We did a number of model runs where we allowed PIG to retreat some distance back, and then we lowered the melt rates in our models. And despite doing that, the grounding line continued to retreat. You can talk about external forcing factors, such climate and ocean effects, and then there are internal factors which are the flow dynamics. What we find is that the internal dynamics of flow are such that the retreat is now self-sustaining.”

In other words, even if the climate somehow miraculously cooled or if the warming ocean somehow managed to melt less ice at the base of the Pine Island Glacier, the glacier would still ultimately destabilize and collapse.

This is hard news, as it has implications for the rest of West Antarctica and, ultimately, about 25 feet worth of sea level rise now locked in the ice. As noted above, the Pine Island Glacier is a massive section of West Antarctica. It is responsible for the draining of about 20% of this section of the continent’s Ice and is one of the primary barriers preventing rapid sea level rise. It is the first domino to start falling. But other dominoes sit in series behind it.

The beginning of PIG’s catastrophic collapse will also likely have major implications for Antarctica’s net ice loss. Gudmundsson’s group found that average melt rates from the Pine Island Glacier are expected to more than quadruple over the next 20 years, increasing to over 100 cubic kilometers of ice loss each year. Total sea level contribution from the Pine Island Glacier alone could be as much as 10 millimeters over the same period, according to model assessments.

This is a large contribution from just one ice sheet. A contribution that is not yet accounted for in global climate simulations for sea level rise. And we have yet to take into account potential additions from other Antarctic melt sources like the adjacent Thwaites glacier or the large glaciers that drain into the Ross Ice Shelf.

In short, if Pine Island has reached the point of no return, then the rest of West Antarctica may well be soon to follow.

Links:

Retreat of Pine Island Glacier Controlled by Marine Ice Sheet Instability

Observations Beneath Pine Island Glacier in West Antarctica and Implications for its Retreat

Pine Island Glacier Retreat “Irreversible”

Ocean Warming Shown to Melt Ice Sheets From Below

Lance-Modis

NASA/UC Study: Warming Ocean Shown to Melt Ice Sheets From Below

NASAwarmocean

(Image source: NASA)

A new study produced in Science shows that a warming ocean is causing at least 55% of the ice melt seen in Antarctica.

The study, run by NASA and Eric Rignot at the University of California, Irvine, shows that basal melting, or melting from below, was responsible for a majority of Antarctic melt. Contact with warm ocean currents was found to erode the ice in a way that was previously undetected. Warming waters, driven by wind and currents, swept against the ice at numerous locations on the ice shelves’ underbellies, carrying away larger and larger volumes of glacial melt.

Until recently, this process was invisible and, therefore, not included in the science of ice sheet dynamics.

The ice shelves, which act as stoppers keeping interior glaciers from sliding into the ocean, are critical to keeping the Antarctic ice sheet healthy. So discoveries of how ice sheets melt are of key importance to both glacial and climate science. And the fact that warming oceans are eroding the ice from underneath is some cause for concern. From NASA:

Antarctica holds about 60 percent of the planet’s fresh water locked into its massive ice sheet. Ice shelves buttress the glaciers behind them, modulating the speed at which these rivers of ice flow into the ocean. Determining how ice shelves melt will help scientists improve projections of how the Antarctic ice sheet will respond to a warming ocean and contribute to sea level rise. It also will improve global models of ocean circulation by providing a better estimate of the amount of fresh water ice shelf melting adds to Antarctic coastal waters.

The image below, compiled by NASA and based on the study’s findings shows how ocean-driven melt rates compare to glacial calving. Overall melt rates are indicated by the red-to-blue color shift and related scale in the upper left corner of the image.

NASAantarcticamelt

(Image source: NASA)

The study built on previous findings in Nature showing that wind-driven ocean currents played a major role in ice sheet melt. Together, these results are challenging previous understandings of ice sheet melt. Past analysis of ice sheet health had assumed that most ice losses occurred during glacial calving events. What Rignot and Pritchard (author of the Nature study) found was that ocean-glacier interaction was a more important factor in overall ice melt.

“This was quite a big gap in our understanding of how the ice sheets interact with their surroundings, and what it shows is that the oceans play a bigger role than we’d previously thought,” said Pritchard about the new study’s results in a Scientific American interview.

Melt From Below

That a warming ocean is a powerful driver of ice melt makes sense. Water contains more heat energy than air and so a given volume of water at a given temperature would have more potential to melt ice than the same volume of atmosphere. Pritchard and Rignot’s findings have major implications for modeling ice sheet melt and could help improve global models. They may also lead the way to a better understanding of ice melt in general.

Sea ice model melt forecasts have also suffered due to a lack of understanding of how the ocean interacts with floating ice. This missing data has led the models to vastly under-estimate sea ice melt in the Arctic. It has also resulted in a general failure in the understanding of how storms affect sea ice floating on the surface of a warming ocean. Scientists and forecasters also often down-play or ignore the impact warm water upwelling, churning or ice sheet contact with warming water currents can have on overall melt rates.

The Pritchard and NASA/Rignot studies of basal melt in Antarctica may, therefore, have broader implications for understanding ice melt around the globe. Most large continental glaciers have contact with the ocean and the sea ice floats on the ocean surface. A dynamic interaction between the ice and ocean is, therefore, ongoing. So improvements to understandings of this interaction are likely to better resolve our forecasts for future melt.

Links:

Oceans Melt Antarctica’s Ice From Below

Antarctic Ice Sheet Loss Driven by Basal Melting of Ice Shelves

Ice Shelf Melting Around Antarctica

Warm Ocean Causing Most Antarctic Ice Shelf Mass Loss

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