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Abnormal Antarctic Heat, Surface Melt, Giant Cracks in Ice Shelves — More Troubling Signs of a World Tipping Toward Climate Chaos

Around its edge zone, and from glacier top to ice shelf bottom, Antarctica is melting. Above-freezing surface temperatures during the austral summer of 2016-2017 have resulted in the formation of numerous surface-melt ponds around the Antarctic perimeter. Large cracks grow through Antarctic ice shelves as warmer ocean currents melt the towering glaciers from below. The overall picture is of a critical frozen region undergoing rapid change due to the human-forced heating of our world — a warming that has brought Antarctica to a tipping point, for such fundamental alterations to Antarctic ice are now likely to bring about a quickening rate of sea-level rise the world over.

Surface Melt Visible From Satellite

During 2016-2017, Antarctic surface temperatures ranged between 0.5 and 1 degree Celsius above the already warmer-than-normal 1979 to 2000 average for most of Southern Hemisphere summer. While these departures for this enormous frozen continent may not sound like much at face value, they’ve translated into periods of local temperatures up to 20 C above average. As a result, measures around Antarctica along and near the coastal zone have risen above the freezing mark on numerous occasions. These periods of much-warmer-than-normal weather have in turn precipitated widespread episodes of surface melt.

antarctica-ice-shelf-melt-rates

(This Antarctic volume-change melt map, which tracks thinning along various coastal ice shelves from 1994-2012, provides a good geographical reference for ice shelves experiencing surface melt or severe rifting. The Amery Ice Shelf [AME], King Baudouin Ice Shelf [BAU], and the Lazarev Ice Shelf [LAZ], stable through 2012, all showed extensive surface melt this summer. Meanwhile the Larsen C Ice Shelf [LAC] and Brunt Ice Shelf [BRU] both feature large rifts that threaten destabilization. Image source: Volume Loss from Antarctica’s Ice Shelves is Accelerating/Sciencemag.org.)

This year, one region in particular has seen temperatures hitting above 0 C consistently: the valley into which the Lambert, Mellor, and Fisher glaciers flow into the Amery Ice Shelf. There, warming has resulted in the formation of multiple large surface-melt ponds. The below image is a January 22nd NASA satellite shot of an approximate 100-by-40-mile section of this glacial outflow zone. The blue areas are melt ponds, some as large as 3 miles wide and 20 miles long.

The Amery Ice Shelf is one of East Antarctica’s largest. Like many of Antarctica’s ice shelves, Amery is melting, with about 46 billion tons of ice lost from this shelf alone each year. As with other Antarctic ice shelves, Amery’s melt is mostly below the surface, caused by warming ocean waters. However, in recent years, considerable surface melt on Amery’s feeder glaciers likely also contributed to significant volume losses in the shelf.

east-antarctic-surface-melt

(Large melt ponds up to 20 miles long cover glaciers flowing into the Amery Ice Shelf on January 22, 2017. Image source: LANCE MODIS.)

Surface melt for Amery has become an increasingly prevalent feature since 2013, with 2017 melt for January 22 the most widespread for any of the past five years in this region. East Antarctica rarely saw large surface melt events prior to the 2000s, and this year’s warming and large melt ponds are a considerable feature. While basal warming is often the cause of the greatest mass losses, surface melt can act like a giant wedge driven into ice shelves, helping to break them up. Melt wedging in glaciers can also increase their forward rate of movement as heat content rises and as the points at which glaciers contact the ground become lubricated.

Moving north toward Dronning Maud Land along the East Antarctic coast, we find another region of surface melt ponding on the King Baudouin Ice Shelf. Nearly as widespread and extensive as the melt on the Amery Shelf’s glaciers, the King Baudouin melt is no less impressive and concerning.

king-baudouin-ice-shelf-melt-summer-2017

(King Baudouin Ice Shelf shows extensive melt ponding along a 40-mile swath of its southwestern corner in January 2017. Image source: LANCE MODIS.)

The largest melt zone shows nearly continuous ponding along a 40-mile-wide diagonal near the ice shelf’s southwestern contact point with East Antarctica’s mainland. A smaller section of melt appears as light blue splotches about 60 miles to the west of the larger melt zone in the image above (for reference, bottom edge of frame represents about 250 miles).

Unlike glacial surface ponding near Amery, melt on King Baudouin occurs directly over the floating ice shelf. This form of melt adds greater stresses as the heavy pools of water can act as wedges that drive gaps in the ice apart. Past instances of widespread surface ponding have occurred in conjunction with the rapid break-up of Larsen ice shelves along the Antarctic Peninsula. Taking a look at past years in the satellite record, we find that this region of King Baudouin has been susceptible to melt since at least 2013. However, the extent of 2017 melt is the greatest in the record for this time of year.

The next ice shelf to the west of King Baudouin, the Lazarev Ice Shelf, shows extensive melt along what appear to be various rifting features streaming out from an open ocean gap where the ice shelf contacts land:

lazarev-ice-shelf-melt-2017

(Ten-mile-long melt ponds visible on the surface of the Lazarev Ice Shelf. Image source: LANCE MODIS.)

Over recent years, the ocean gap — visible as a dark section in center-bottom frame of the image above — has slowly grown larger. There, open ocean water has gradually taken up a larger and larger section of Lazarev’s land-contact point. Meanwhile, from 2013 to 2017, melt ponds have tended to radiate out from this open gap region along rifts in the ice shelf structure during summer as air temperatures have risen above freezing.

This year, melt appears to be quite extensive with two parallel 10-mile-long melt ponds filling in rift features with many smaller melt ponds interspersed. The open ocean gap combined with rifts filling with what is now seasonal melt water gives the overall impression of a rather weak structure.

Ice Shelves Cracking Up

Though regions on or near the Amery, King Baudouin and Lazarev Ice Shelves show the most obvious surface melt features, large melt ponds also formed near the Fimbul Ice Shelf. Ponds also formed during a Föhn wind event near the Drygalski Ice Tongue. Even as such instances of surface melt became a more obvious feature across Antarctica, at least two large ice shelves were run through by growing rifts that threatened their stability.

One such rapidly-expanding rift forced the British Halley VI research team to evacuate their base of operations on the floating Brunt Ice Shelf. This rift, which had until late 2016 been growing only gradually, doubled in length in less than three months. Its gaping chasm threatened to cut the expedition off from the Antarctic mainland and set it adrift at sea — forcing an early evacuation as a precaution.

(Drone footage of Brunt Ice Shelf’s rapidly growing crack. From October through early January, the crack doubled in size from 22 kilometers in length to 44 kilometers. Video source: Antarctic Survey.)

Meanwhile, a large crack that will soon result in a 2,000-square-mile iceberg breaking from the Larsen C Ice Shelf recently grew by another six miles to 100 miles long. The Connecticut-sized ice chunk now only hangs by a 15 to 20 mile thread. With the loss of this very large segment of ice, researchers are concerned that Larsen C may destabilize and ultimately succumb to the fate of Larsen A and Larsen B — breaking into thousands of separate icebergs and floating away into the Southern Ocean.

Signs of Melt, Destabilization as More Above-Freezing Temperatures are on the Way

With so many large melt ponds and melt-related rifts forming in Antarctica’s ice shelves, it’s worth considering that these shelves serve as a kind of door jam holding large glaciers back from flooding into the ocean. And as more ice shelves melt and destabilize, the faster these glaciers will move and the faster the world’s oceans will rise.

So much widespread melt and rifting of Antarctica’s ice shelves is a clear warning sign. And if enough of the ice shelves go, then rates of sea-level rise could hit multiple meters this century.

antarctic-warming

(Many locations along the coast of Antarctica will see 5-15 C above-average surface temperatures this week, a continuation of a strong surface melt pressure for the austral summer of 2016-2017. Image source: Climate Reanalyzer.)

This week, another spate of near- or above-freezing temperatures will run along the coastal regions of both east and west Antarctica, so the amazing atmospheric melt pressure that we are now seeing should continue to remain in play at least for the next seven days as austral summer continues. As for the melt pressure coming from the warming ocean beneath the ice shelves — that is now a year-round feature for many locations.

Links:

Climate Reanalyzer

Volume Loss from Antarctica’s Ice Shelves is Accelerating

LANCE MODIS

Antarctic Survey

Rapidly Growing Crack in Brunt Ice Shelf Forces Evacuation of Halley Research Station

Larsen C Ice Shelf Crack Just Grew By Another 6 Miles

Did Föhn Winds Just Melt 2 Miles of Antarctic Surface Ice in Just One Day?

Hat tip to Shawn Redmond

Hat tip to Jeremy in Wales

Hat tip to Colorado Bob

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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

At Least 20-75 Feet of Sea Level Rise Already Locked In? Putting Climate Central’s Surging Seas Into Context

“There are some recent modeling efforts that now show you could get a section of the Antarctic ice sheet, several meters worth of sea level rise, to go in a decade. We used to think it was centuries.” — Andrea Dutton Geochemist at the University of Florida.

*  *  *  *  *

Recent reports out from Climate Central and supported by the work of experts show that a sea level rise of at least 6 meters could already be locked in. And as bad as that sounds, a six meter sea level rise from the warming already set in motion by high atmospheric greenhouse gas levels and likely to come from further human emissions could be a best-case or even unrealistic scenario.

To get an understanding as to why so much water may be heading toward the coastal cities of the world, enough water in a 6 meter rise to set off a mass migration of hundreds of millions away from the world’s coasts (just 1.1 meters is enough to flood out 150 million people), it helps to take a good, hard look at paleoclimate. In studying past, warmer, climate states, we can get an idea how much additional sea level rise might be in store. When looking at these past climates for comparison, the key readings to keep in mind are — temperature, greenhouse gas level, and related sea level.

A Question of Whether We Lock in Greenhouse Gas Levels Comparable to Past Climates

Starting with the current climate that is now being rapidly warmed by human fossil fuel burning, we find that this year peak monthly CO2 levels hit near 404 parts per million. It’s a value fast approaching the top of this key greenhouse gas’s range during the Pliocene around 3.5 million years ago. A time when temperatures were 2-3 degrees Celsius hotter and sea levels were between 25 and 75 feet higher than they are today.

Virginia Beach 6 meter sea level rise

(What Virginia Beach looks like after 6 meters of sea level rise. Notably, about everyone I knew as a child or who still lives in VB now is under water in this scenario. Image source: Climate Central.)

Looking at the climate situation in this way tends to elicit a bit of an ‘oh crap’ response. And it should. For all other things being equal, if CO2 levels were to remain so high over the course of a few Centuries, that’s where we’re headed. Toward a world with 2-3 C hotter temperature and 25 to 75 foot higher seas.

But the atmosphere of today is only a rough allegory to that of Pliocene times. In addition to CO2, our airs now host expanding volumes of other greenhouse gasses — exotic and common. A vast majority of which are emitted as a result of fossil fuel burning, extraction, and industrial processes. So to compare our atmosphere to that of the period around 3.5 million years ago and expect the same results with regards to temperature and sea level would be unrealistic. Current methane readings alone — in excess of 1800 parts per billion — now hit levels likely twice that of the Pliocene. And methane is a greenhouse gas with a global warming potential equal to 20 to 120 times that of CO2 over timescales relevant to current human civilization.

As a result of this additional accumulation of methane and other gasses, this year’s atmosphere is a closer allegory to past atmospheres containing an equivalent of about 484 parts per million CO2 (CO2e). Such times, occurring 15-25 million years ago, hosted sea levels that were more than 100 feet (and possibly as much as 200 feet) higher than today.

It is for this reason that we should view Climate Central’s recent and excellent report on sea level rise — based on Paleoclimate and predicting that at least 20 feet of sea level rise could already be locked in — with a bit of concern. At issue with the report are two factors. The first is that the study bases its findings on predicted temperature increases for the 21st Century only. A process established by IPCC-based studies in which it is assumed that 2 degrees Celsius warming over the course of this Century is, perhaps, the best possible target we can hit through a pretty rapid transition to a zero or near-zero carbon civilization. Implied in this IPCC approach is limiting global CO2 accumulation to 450 parts per million or less. A level that also implies a 530 to 550 parts per million CO2e when other gasses are added in unless all the methane overburden falls out due to its short atmospheric lifetime (about 8 years). A dicey assumption at best considering that at least some and possibly all of that overburden could be maintained by feedbacks now at play in the Arctic and in the world’s land and ocean systems.

Miami submerged 6 meters

(At six meters of sea level rise, Miami is completely submerged. Image source: Climate Central.)

In worse cases, we could see the methane overburden expand in the event that the Arctic carbon stores are less stable than we’d hoped. So while 450 parts per million CO2 might limit us to between 2 and 2.3 C warming this Century, 530 to 550 parts per million CO2e gets us to 2.2 to 2.9 C.

The second issue is that we are only looking at warming for the 21st Century. Due to the long term warming impact of CO2 and other greenhouse gasses on the climate system in total, each 1 C worth of warming this Century implies about 2 C worth of warming long term (ESS sensitivity). So hitting the 2 C target by 2100 gets you to 4 C after many Centuries. And hitting a 550 parts per million CO2e threshold means about 2.7 to 2.9 C 21st Century warming and 5.5 to 5.8 C long term warming. An upper range that is nearly enough to melt all the land ice on Earth and raise sea levels by nearly 240 feet.

How Fast Could Sea Levels Rise?

At least 6 meters indeed! In the 550 parts per million CO2e case, we have one of the better global human carbon emissions scenarios meeting with one of the somewhat more pessimistic Earth Systems response scenarios (but not the worst case) for an absolutely terribly catastrophic outcome. An outcome made even more terrifying by the fact that it is in the mid-to-low range of overall projected greenhouse gas forcings for this Century. In other words, 2 C warming this Century can start to look like a pretty bad outcome for the long haul and we’d probably best be trying to hit well below the implied 450 ppm CO2 target (as Hansen and others have warned). And to this point, we had better move very fast on emissions reductions, because the longer even current greenhouse gas levels are maintained the more likely we hit ice sheet destabilizations that push world ocean levels closer and closer to the Pliocene’s or Miocene’s swollen seas.

Post-Glacial_Sea_LevelTemperature Change End of Last Ice Age

(Just 1 C worth of global warming from 22,000 years BP to 15,000 years BP was enough to set off rapid sea level rise during the end of the last ice age. We are fast approaching the 1 C warmer than 1880s thresholds now. Image source: Commons and Livescience.)

Which brings us to a final question hinted at in the header — how fast could sea levels rise if human forced warming approaches 2 C or more this Century? The modelling efforts Dutton hinted at shows that West Antarctica alone can contribute meters of sea level rise over the course of just decades. And going back to paleoclimate studies of the end of the last ice age we find hints that somewhere between 1 and 2 C worth of warming can trigger very large and rapid glacial outbursts (that then increased sea levels by as much as 16 feet per Century). Finally, recent glacier surveys from Antarctica to Greenland have found extensive and expanding destabilization. Efforts and evidence that imply the 39 inches of sea level rise predicted by IPCC this Century may be quite conservative, even under the better case emissions scenarios.

Links:

Surging Seas

Sea Level Could Rise at Least 6 Meters

Commons

Livescience

Antarctica and Greenland’s Simultaneous Destabilization

Concern Over Catastrophic Methane Release

A Faustian Bargain on the Short Road to Hell

The Keeling Curve

Warm Water Rising From the Depths: Much of Antarctica Now Under Threat of Melt

Antarctica. A seemingly impregnable fortress of cold. Ice mountains rising 2,100 meters high. Circumpolar winds raging out from this mass of chill frost walling the warm air out. And a curtain of sea ice insulating the surface air and mainland ice sheets from an increasingly warm world. A world that is now on track to experience one of its hottest years on record.

Antarctica, the coldest place on Earth, may well seem impregnable to this warming. But like any other fortress, it has its vulnerable spots. In this case, a weak underbelly. For in study after study, we keep finding evidence that warm waters are rising up from the abyss surrounding the chill and frozen continent. And the impact and risk to Antarctica’s glacial ice mountains is significant and growing.

Rapid Break-up of Ice From Filchner Ronne Ice Shelf in Jan 2010

(Collapse of ice structure at the leading edge of the Filchner-Ronne Ice Shelf adjacent to a rapidly warming Weddell Sea during January of 2010. A new study has found warm water upwelling from the Circumpolar Deep Water is rapidly approaching this massive ice shelf. Loss of Filchner-Ronne and its inland buttressed glaciers would result in 10 feet of sea level rise. Image source: Commons.)

For a study this week confirmed that Antarctica is now seeing a yearly loss of ice equal to one half the volume of Mt Everest every single year. A rate of loss triple that seen just ten years ago. An acceleration that, should it continue, means a much more immediate threat to coastal regions from sea level rise than current IPCC projections now estimate.

Shoaling of the Circumpolar Deep Water

The source of this warm water comes from a deep-running current that encircles all of Antarctica. Called the Circumpolar Deep Water, this current runs along the outside margin of the continental shelf. Lately, the current has been both warming and rising up the boundaries of the continental zone. And this combined action is rapidly bringing Antarctica’s great ice sheets under increasing threat of more rapid melt.

According to a new study led by Sunke Schmidtko, this deep water current has been warming at a rate of 0.1 degrees Celsius per decade since 1975. Even before this period of more rapid deep water warming, the current was already warmer than the continental shelf waters near Antarctica’s great glaciers. With the added warming, the Circumpolar Deep Water boasts temperatures in the range of 33 to 35 degrees Fahrenheit — enough heat to melt any glacier it contacts quite rapidly.

Out in the deep ocean waters beyond the continental shelf zone surrounding Antarctica, the now warmer waters of this current can do little to effect the great ice sheets. Here Sunke’s study identifies the crux of the problem — the waters of the Circumpolar Deep Water are surging up over the continental shelf margins to contact Antarctica’s sea fronting glaciers and ice shelves with increasing frequency.

In some cases, these warm waters have risen by more than 300 feet up the continental shelf margins and come into direct contact with Antarctic ice — causing it to rapidly melt. This process is most visible in the Amundsen Sea where an entire flank of West Antarctica is now found to be undergoing irreversible collapse. The great Pine Island Glacier, the Thwaites Glacier and many of its tributaries altogether composing enough ice to raise sea levels by 4 feet are now at the start of their last days. All due to an encroachment of warm water rising up from the abyss.

Rivers of Ice Antarctica

(Antarctic rivers of ice. Rising and warming waters from the Circumpolar Deep Water along continental margins have been increasingly coming into contact with ice shelf and glacier fronts that float upon or face the surrounding seas. The result has been much higher volumes of melt water contributions than expected from Antarctica. Image source: University of California.)

But the warm water rise is not just isolated to the Amundsen Sea. For Sunke also found that the warm water margin in the Weddell Sea on the opposite flank of West Antarctica was also rapidly on the rise. From 1980 to 2010, this warm water zone had risen from a depth of about 2100 feet to less than 1100 feet. A rapid advance toward another massive concentration of West Antarctic ice.

The impacts of a continued rise of this kind can best be described as chilling.

Sunke notes in an interview with National Geographic:

If this shoaling rate continues, there is a very high likelihood that the warm water will reach the Filchner Ronne Ice Shelf, with consequences which are huge.

Filchner Ronne, like the great Pine Island Glacier, has been calving larger and larger ice bergs during recent years. Should warm waters also destabilize this vast ice shelf another 1.5 feet of sea level rise would be locked in due to its direct loss. Including the massive inland glaciers that Filchner Ronne buttresses against a seaward surge, much larger than the ones near the Amundsen sea, would add a total of 10 feet worth of additional sea level rise.

Together, these destabilized zones would unleash much of West Antartica and some of Central Antartica, resulting in as much as 14 feet of sea level rise over a 100 to 200 year timeframe. This does not include Greenland, which is also undergoing rapid destabilization, nor does it include East Antarctica — which may also soon come under threat due to the encroachment of warm waters rising from the depths.

Are IPCC Projected Rates of Sea Level Rise Too Conservative?

The destabilization of glaciers along the Amundsen sea, the imminent threat to the Filchner Ronne Ice Shelf, and the less immediate but still troubling threat to East Antarctica’s glaciers, together with a rapidly destabilizing Greenland Ice Sheet, calls into question whether current IPCC predictions for sea level rise before 2100 are still valid.

IPCC projects a rise in seas of 1-3 feet by the end of this Century. But much of that rise is projected to come from thermal expansion of the world’s oceans — not from ice sheet melt in Antarctica and Greenland. Current rates of sea level rise of 3.3 milimeters each year would be enough to hit 1 foot of sea level rise by the end of this Century. However, just adding in the melting of the Filchner Ronne — a single large ice shelf — over the same period would add 4.4 milimeters a year. Add in a two century loss of the Amundsen glaciers — Pine Island and Thwaites — and we easily exceed the three foot mark by 2100.

Notably, this does not include the also increasingly rapid loss of ice coming from Greenland, the potential for mid century additions from East Antarctica, or lesser but still important additions from the world’s other melting glaciers.

Such more rapid losses to ice sheets may well reflect the realities of previous climates. At current CO2e levels of 481 ppm (400 ppm CO2 + Methane and other human greenhouse gas additions) global sea levels were as much as 75-120 feet higher than they are today. Predicted greenhouse gas levels of 550 to 600 ppm CO2e by the middle of this century (Breaking 550 ppm CO2 alone by 2050 to 2060) are enough to set in place conditions that would eventually melt all the ice on Earth and raise sea levels by more than 200 feet. For there was no time in the past 55 million years when large ice sheets existed under atmospheric CO2 concentrations exceeding 550 parts per million.

Glaciologist Eric Rignot has been warning for years that the IPCC sea level rise estimates may well be too conservative. And it seems that recent trends may well bear his warnings out. If so, the consequences to millions of people living along the world’s coastlines are stark and significant. For the world, it appears we face the increasing likelihood of a near-term inland mass-migration of people and property. A stunning set of losses and tragedy starting now and ongoing through many decades and centuries to come.

Links:

Warming Seas Drive Rapid Acceleration of Melting Antarctic Ice

Mass Loss of the Amundsen Sea Embayment of West Antarctica

Multidecadal Warming of Antarctic Waters

Research Casts Alarming Light on Decline of West Antarctic Glaciers

Antarctic Ice Shelf Being Eaten Away by Sea

Greenland Ice Loss Increases Fivefold From Late 1990s, West Antarctica Not Far Behind

In the early 1990s, it would have been hard to imagine the rates of glacial ice loss we are seeing now.

There were few ways to accurately measure the Greenland Ice Sheet’s mass. Snow fell, glaciers calved. But observations seemed to show that the great, cold ice pile over Greenland was in balance. Snow gathered at the top, glaciers calved at the edges, but human heating of the atmosphere had yet to show plainly visible effects.

At that time, climate scientists believed that changes to the ice, as a result of human caused heating, would be slow and gradual, and would probably not begin to appear in force until later in the 21st Century.

Greenland Jacobshavn July 30 2014

(Extensive surface melt ponding, dark snow near the rapidly melt Jakobshavn Glacier on the West Coast of Greenland in early August of 2014. Image source: LANCE MODIS.)

Ice Sheet Response Starts Too Soon

By the late 1990s, various satellites had been lofted to measure the gravity, mass and volume of structures on the Earth’s surface. These sensors, when aimed at the great ice sheets, found that Greenland, during a period of 1997 to 2003 was losing mass at a rate of about 83 cubic kilometers each year.

This rate of ice loss was somewhat small when compared to the vastness of the ice sheet. But the appearance of loss was early and, therefore, some cause for concern. More monitoring of the ice sheet took place as scientists continued their investigation, for it appeared that the ice sheet was more responsive to human warming than initially believed.

A Doubling After Just Six Years

By 2009 another set of measures was in and it found that the six year period from 2003 to 2009 showed a near doubling of ice mass loss from the Greenland Ice Sheet. Rates of loss had jumped from 83 cubic kilometers each year to around 153 cubic kilometers. The doubling caused consternation and speculation among climate scientists. Greenhouse gas heat forcing was rapidly on the rise and the world’s oceans were warming faster than expected as human emissions continued along a worst case scenario path. It appeared that the ocean was delivering heat to the ice sheet bases even as atmospheric warming was melting larger areas upon the ice sheet surface.

These changes to the massive ice sheets were occurring far more rapidly than previously considered.

Edge of Greenland Ice Sheet

(Hundreds foot high edge of the Greenland Ice Sheet in Kangerlussuaq as seen at the end of a long valley and across a cold estuary. Image source: EISCAT Scientific Association.)

The potential for a 3, 6, or even 9 foot or more sea level rise by the end of the 21st Century was raised. Perhaps even more ominous, global climate models were showing that rapid ice melt in Greenland and West Antarctica, should it occur, would play havoc with world weather systems. It was this jump in ice loss, in part, that spurred climate scientist and then head of NASA GISS, Dr. James Hansen to write his book The Storms of My Grandchildren as a warning that rapid mitigation in human greenhouse gas emissions along with a stabilization of atmospheric CO2 at 350 ppm would probably be needed to prevent severe consequences from human-caused warming.

But humans kept emitting at a break-neck pace, spending far more money to build coal, gas and oil based technology, than to reduce energy consumption through efficiencies or behavioral change or to invest in alternatives like wind and solar.

Melt Rates Surge Yet Again

And so, by January of 2014, heat forcing had continued to accumulate at a very rapid pace. CO2e heat forcing had spiked to 481 ppm, enough to melt the entire Greenland Ice Sheet and much of Antarctica as well, if maintained or increased over a long period.

And the Greenland Ice sheet was, indeed, melting at an ever faster clip. For the most recent assessment found that the loss rate from Greenland had again more than doubled — hitting a 375 cubic kilometer per year average during the period of January 2011 through January of 2014.

Greenland Ice Sheet Elevation Change

(Greenland Ice Sheet elevation change in meters as found in a recent report by the Alfred Wegner Institute. Note that all Greenland edge zones are now experience elevation losses. Due to higher elevations at the center of the ice sheet, elevation loss at the edge has an effect that speeds ice sheet motion toward the sea. The effect is similar to pushing down the edge of a plastic swimming pool, but on a much larger scale and with somewhat slower moving ice.)

It was an extraordinary rate of melt now 4.7 times faster than in the period from 1997 to 2003 and 2.5 times faster than during 2003 to 2009. But, likely, it is but one more milestone on the path to even faster melt.

The same study that found the Greenland melt acceleration also saw a tripling of the melt rate of West Antarctic since 2003 to 2009. Together, the ice sheets were found to contribute a combined mass loss of 503 cubic kilometers per year between Greenland and West Antarctic. This vast, and still apparently rising, loss now meant that the two great ice sheets were contributing at least one millimeter per year to sea level rise.

Likely Grim Future For Sea Level Rise

It is likely that mass rate losses will continue to increase until some kind of break or negative feedback comes into play. Similar rates of melt increase would mean an annual 5-8 millimeter sea level rise by 2035 due to Greenland and Antarctic melt on top of a 2-3 millimeter sea level rise from thermal expansion of the oceans and from other melt sources. But even taking into account the cooling effect at the ocean surface from ice melt and fresh water floods, one could easily envision the feared 1-3 foot sea level rise by sometime near mid century and the even more concerning 3-9 foot sea level rise amidst a very intense battle between hot and cold weather systems through to century’s end.

As of 2014, it appears the conditions leading up to the warned of “Storms of My Grandchildren” are well in play and rapidly building.

Links:

Alfred Wegner Institute: Elevation Change of the Greenland Ice Sheet

Greenland Ice Loss Doubles From Late 2000s

LANCE MODIS

The Storms of My Grandchildren

EISCAT Scientific Association

Hat Tip to TodaysGuestIs

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

“Our new results suggest that the Antarctic Ice Sheet is more unstable than previously considered…” — Peter Clark, Paleoclimatologist at Oregon State University

*    *    *    *    *

Massive glacial destabilization and irreversible collapse caused by human warming. That’s what a flurry of recent studies issued by NASA’s Jet Propulsion Laboratory found is now happening to vast sections of Antarctica’s towering glaciers.

The NASA climate scientists found that rapid human warming of the deep ocean was resulting in hotter than usual water upwelling beneath the ocean-fronting glaciers of Antarctica. The warmer waters ate away at the great glaciers from underneath, making them less stable and propelling them with ever-higher velocity toward the world’s oceans. The studies, led by Eric Rignot, concluded that large sections of Antarctica were now destabilized and that six key glaciers representing what could well be termed the entire flank of West Antarctica were now locked in an unstoppable plunge into the ocean.

These glaciers in irreversible collapse combined with a growing number of destabilized and destabilizing glaciers all around Antarctica and northward to Greenland to represent an extreme risk for a much more rapid than expected sea level rise this century.

Now a new study published this week in the prestigious science journal Nature adds to what has become an extraordinary torrent of evidence for heightening risks to speeding human-spurred sea level rise.

Antarctica glacial velocity map

(Antarctica glacial velocity map composed by Eric Rignot in 2011. Blue = fast. Brown = slow. Note the numerous high-speed glacial flows plunging deep into Antarctica. By the 2010s, Antarctica was losing between 1,300 and 2,000 gigatons of ice each year. Image credit: Antarcticaglaciers.org.)

A Glimpse into Earth’s Past Provides Stark Evidence For a Human-Warmed Future

The study, entitled Millennial-Scale Variability in Antarctic Ice Sheet Discharge During the Last Deglaciation, and published in Nature, took a closer look at Antarctic ice sheet instability and its contribution to sea level rise during the end of the last ice age by taking sediment cores from iceberg rafted debris (IBRD) fields around the frozen continent. These fields contained minerals left by melting glaciers discharged into the Southern Ocean during the major glacial melt events at the end of the last ice age and provide a good proxy for the rate of glacial discharge from Antarctica.

Analysis of these sediment cores resulted in the finding that Antarctica experienced 8 separate large glacial outburst events during the end of the last ice age. These events began about 20,000 years ago and ended 9,000 years ago. This is directly counter to conventional thinking that had assumed Antarctic melt started late and ended early during the last glacial melt period. It also hints that the Antarctic ice sheet is far less stable that previously assumed, making it much more vulnerable to current, human-caused heat forcings.

Each large outburst event contributed significantly to global sea level rise. The largest and most violent event was found to have occurred around 14,900 years ago. Lasting 350 years, this single episode, known as meltwater pulse 1A, resulted in a 50 foot sea level rise, pushing global oceans higher by 14.2 feet per century. It was previously unknown that Antarctica contributed in any way to this rapid sea rise event. But large deposits of iceberg sediment during this time of surging oceans provides strong evidence that Antarctica was a major contributor.

Post-Glacial_Sea_Level

(Pace of post glacial sea level rise since the end of the last ice age. Note the steep rise in sea levels occurring in conjunction with meltwater pulse 1A, a pulse that scientists now know included a major contribution from Antarctic melt. Image source: Commons.)

Professor Clark of Oregon State’s College of Earth, Ocean and Atmospheric Sciences who contributed to the paper noted:

“During that time, the sea level on a global basis rose about 50 feet in just 350 years – or about 20 times faster than sea level rise over the last century. We don’t yet know what triggered these eight episodes or pulses, but it appears that once the melting of the ice sheet began it was amplified by physical processes.”

Implications for Current-Day Human Warming

At first blush, the findings of this study may seem innocuous. But upon reflection, one quickly comes to the conclusion that they are rather stark.

In total, about 200 feet of potential sea level rise is currently locked in all of Antarctica’s ice. This compares to Greenland which, if it completely melted, would contribute about 24 feet to sea level rise. Until recently, it was assumed that this large store of ice in Antarctica was relatively stable and responded only slowly to climate perturbations.

The first challenge to the notion of Antarctic ice sheet stability came in 1968 when glaciologists began issuing warnings that the West Antarctic Ice Sheet was unstable. But, until recent years, this instability lacked an observed physical mechanism to explain what appeared to be an ongoing and increasingly rapid glacial rush toward the sea. By the mid 2000s, scientific reports began to emerge showing that warm water upwelling along the coasts of Antarctica was eating away larger and larger chunks of the great glaciers’ bases and speeding their flow to the sea. This year, a flurry of reports sounded a death knell for entire sections of West Antarctic ice, locking in many feet of sea level rise with more likely to come.

Temperature increase over last 22,000 years

(Temperature and CO2 increase from 22,000 YBP through 6,000 YBP. Note that major glacial outburst events in Antarctica began after only .2 C of atmospheric warming and 10 ppm of CO2 increase around 20,000 years ago. Such a response shows a very high degree of glacial and Earth Systems climate sensitivity. Also note that total warming over a 12,000 year timeframe was 3.7 C. Warming of 4, 6 and even 9 C is possible by the end of this Century under BAU human greenhouse gas forcing. Image source: Nature via Skeptical Science.)

But until this recent Nature paper, such a rapid destabilization of Antarctica’s massive glaciers was without a paleoclimate context. For few studies had challenged an assumed but sparsely supported perception of past Antarctic ice sheet stability. To the contrary, the paper found an Antarctic ice sheet that was very sensitive to warming. The ice sheet issued its first major glacial outburst 20,000 years ago as the world showed its first hint of thaw from a great ice age. The giant glaciers continued their lashing out in 8 major events until warming stopped with the advent of the Holocene around 9,000 years ago. At that point, Earth’s climate had begun to settle into a new equilibrium and Antarctica quieted its grumbling.

Now that humans are warming the atmosphere and oceans at a pace at least 30 times that of the last ice age, we are discovering that Antarctica in the deep past showed a major destabilization response to even the slightest hint of warming.

A Warming Ocean is Likely Antarctica’s Soft Underbelly

Rapidly accumulating evidence that ocean warming is providing a powerful blow to the world’s glaciers combines with the recent study to provide a stark implication — any addition to atmospheric heat is rapidly transferred to the world’s oceans which, in turn, goes to work melting ocean-contacting glaciers. Furthermore, glacial destabilization is likely to remain in play so long as the global energy imbalance toward continued warming remains in force and destabilized glaciers haven’t yet hit the ocean. As such, we should consider that start time for glacial destabilization and increasing rates of sea level rise to be now and not in some distant, far off, future.

Glacial systems may well present considerable atmospheric inertia. But when presented with warming waters, the glaciers must yield. This makes sense as water’s heat capacity is four times greater than that of air. So the melting force of water just one degree C above freezing is about four times that of the same volume of air at the same temperature. Glaciers in constant contact with the potent heat capacity of warming oceans essentially don’t stand a chance. And with many of Antarctica’s glaciers directly in the firing line of waters warmed by human greenhouse gas forcing rising from the deep ocean, it would appear, at this time, that the great frozen continent may well have a very soft underbelly.

Antarctic Waterfall

(Waterfall spilling from the heart of a melting Antarctic glacier and into the Southern Ocean. Image source: Antarctica.gov.au)

Inertia Not So Strong as the Forcing; Stark Implications For Sea Level Rise

Since so much has happened over the past year, it is useful to put the current state of science into an overall context. In doing so we should consider these scientific findings:

  1. Large portions of Antarctica are already undergoing destabilization or irreversible collapse.
  2. In the deep past, Antarctica responded very rapidly to even a small global temperature change and remained unstable so long as warming continued.
  3. This rapid glacial response and destabilization was likely due to a broad basal exposure to warming oceans.
  4. The current pace of human warming is now 30 times faster than at the end of the last ice age.
  5. The deep ocean is accumulating heat faster than any other Earth System.
  6. At peak, the most violent glacial outburst flood events included glacial discharges from Antarctica and pushed sea levels higher by 14.2 feet each century during the end of the last ice age.
  7. Current human CO2 heat forcing at 400 ppm + is enough to raise sea levels by 75 feet according to paleoclimate estimates.
  8. Current human CO2e heat forcing at 481 ppm + is enough to raise sea levels by 120 feet according to paleoclimate estimates.

Considered together, these points would seem to indicate that glacial inertia to heat forcing is not so great as previously hoped. More likely, the energy balance of the Earth System more rapidly responds to total heat content, energy imbalance, and pace of heat accumulation than previous sensitivity estimates assumed. If this meta-analysis is true, and it seems to be based on a growing pile of evidence, sea level rise for the current century is likely to be far greater than previously anticipated by scientific assessments. The top range of a 3 foot sea level rise for this century under IPCC modeling is likely, given current realities, to instead be a low estimate. A more realistic range, given a greatly reduced true glacial inertia, is probably 3-9 feet through 2100 with higher outside potentials during large glacial outburst flood events.

Given changing ocean and atmospheric conditions together with the rising potential of large rainfalls over certain glacial zones during summer as the 21rst century progresses, climate analysts should consider such large glacial outburst floods to be a potential high risk event under current extreme human warming. It is also worth noting that these glacial systems have probably never experienced a set of forces so powerful or rapid as they are likely to face as the 21rst century progresses. Recent scientific assessments are essentially playing catch-up to these new and emerging realities.

Links:

Grim News From NASA: West Antarctic’s Entire Flank is Collapsing into the Southern Ocean

Millennial-Scale Variability in Antarctic Ice Sheet Discharge During the Last Deglaciation

Commons

Nature

Skeptical Science

Antarctica.gov.au

Antarctic Ice Sheet Unstable at End of Last Ice Age

Antarcticaglaciers.org

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

Science has confirmed it. Human-caused warming is killing Antarctica’s massive Pine Island Glacier (PIG). And this week’s release of a chunk of ice larger than Guam into the southern ocean is just one of the many major losses that will occur as part of what is now an inevitable demise of one of the world’s greatest glaciers.

(CNN provides this stunning NASA imagery sequence of the break-off of B-31, a 12×24 mile iceberg from the, now doomed, Pine Island Glacier.)

Heat-Charged Blow to The Soft Underbelly of Antarctic Ice Shelves

As human greenhouse gas emissions caused the world’s oceans to warm, upwelling currents delivered a portion of that heat to the continental shelf zone surrounding Antarctica. A fortress of ice, numerous glacial ice shelves thrust out from this frozen land and drove deep into the sea floor. Ocean-fronting glaciers featured submerged sections hundreds of feet below the sea surface.

The warming currents encountered these massive ice faces, eroding their undersides and providing pathways for ocean waters to invade many miles beneath the glaciers. These invasions subjected the vulnerable ice shelves not only to the heat forcing of an ever-warming ocean, but also to wave and tidal stresses. The reduction in grounding and the constant variable stresses set the glaciers into a rapid seaward motion.

Antarctica’s most vulnerable glaciers lie along its western out-thrust. Two, Thwaites and the Pine Island Glacier, have recently seen very rapid increases in forward speed. Of these, the Pine Island Glacier, according to a recent study, is undergoing the process of an irreversible collapse. What this means is that the glacier’s speed of forward motion is now too great to be halted. Inevitably, even if the climate were to cool, the entire giant glacier will be launched into the world’s oceans where it will entirely melt out.

PIG basal melt

(Pine Island Glacier underwater melt dynamics. Image source: Nature)

Guam-Sized Chunk of Ice to be One of Many

The Pine Island Glacier is massive, covering a total area of 68,000 square miles and, in some locations, rising to over 2,000 feet in height. It represents 10% of all the ice in the West Antarctic Ice Sheet, holding enough liquid water to raise sea levels by between 1 and 2.5 feet all on its own. And the now destabilized PIG is bound to put added stresses on the adjacent Thwaites glacier together with almost the entire West Antarctic ice system.

Over recent years, PIG’s forward speed has accelerated. Increasing forward velocity by 73 percent from 1974 to 2007. Surveys made since that time show an even more rapid pace. By January of this year, studies were finding that PIG had entered a sate of irreversible collapse. So it is little wonder that enormous chunks of ice are breaking off from this massive glacier and drifting on out into the Southern Ocean.

As of early this week, the immense ice island dubbed B31 measuring 12×24 miles in size (nearly 290 square miles), slid off its temporary grounding on the sea bottom and began its journey out into the Southern Ocean. There it will remain for years, plaguing the world’s shipping lanes as it slowly disintegrates into a flotilla of icebergs. It is just the most recent event in the now ongoing decline of PIG. And we can expect many, many more major ice releases as this vast Antarctic glacier continues its dive to the sea.

Links:

Humongous Iceberg Slowly Drifts Away From Antarctica

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

Nature

Retreat of Pine Island Glacier Controlled by Marine Ice Sheet Instability

The Pine Island Glacier

The Thwaites Glacier

Hat tip to Colorado Bob who’s been tracking PIG since 1994

 

 

A Tale of Two Ice Caps: As Arctic Ocean Heads Toward Ice-Free Summers, New Study Shows Human Warming Takes Out 56% of Antarctic Sea Ice by 2050

Thus far, the Arctic has been ground zero for human-caused climate change. A combination of sea ice melt, albedo loss, a warming ocean that transports heat beneath a melting ice cap, regions of Jet Stream retreat into the far north, and an overburden of greenhouse gasses near the pole, among other factors, have all resulted in a very rapid pace of local warming.

Global temp anomaly

(Global surface temperature anomaly over the last month features a high degree of, very visible, Arctic heat amplification. Most global warming models show the Arctic warms rapidly first under human warming. Then, as second stage warming progresses, heat begins to spike over other regions of the globe. Image source: NOAA ESRL.)

While global warming totals about .8 C above the 1880s average, about 1/6th the difference between now and another ice age, but on the side of hot, Arctic warming has pushed above 3.0 C during the same time period. And as the Arctic is warming four times as fast as the rest of the globe, many of human climate change’s most extreme impacts are now visible there.

The Arctic’s Massive and Dramatic Loss of Sea Ice

A primary measure of Arctic warming has been sea ice melt. And Arctic sea ice melt during the past few decades has been nothing if not dramatic. By end of summer 2012, a time when sea ice melt is most intense, area and extent totals had fallen more than 50% below their 1979 measurements. Meanwhile, Arctic sea ice volume, a measure of area + thickness, had fallen by as much as 80%. These losses are dramatic and raise the possibility for ice free summers, if the weather conditions line up, during a period between now and 2030.

arctic-death-spiral-1979-201302

(Arctic death spiral showing sea ice volume measurements for all months from 1979 through early 2013. Image source: Skeptical Science. Data source: PIOMAS.)

Thin Ice Over Warming Water

As hinted at above, the Arctic has a number of unique characteristics that make it vulnerable to rapid warming in the context of a more slowly warming globe. And chief among these is geography — warmer continents surrounding a mostly frozen ocean.

A lion’s share of the northern polar ice cap area is composed of sea ice. By area, even after the stunning losses seen since 1979, the sea ice cap composes about 10.5 million square kilometers on average. Greenland, in contrast, only boasts an ice sheet of around 2 million square kilometers. This large layer of ice provides an amazing amount of cooling just due to its white, reflective properties. In the past, this albedo has helped to maintain a zone of very cold air centered almost directly over the pole.

But this Arctic system of cold amplification and northern refrigeration has a major Achilles heel. For the sea ice sits upon an ocean that is much closer to the melting point of water than any frozen land mass. Furthermore, all ocean systems are connected and, to one degree or another, readily transport heat.

Melting Arctic Sea Ice

(Melting Arctic sea ice during summer. Image source: NASA.)

In the context of human-caused warming, the majority of northern polar ice area is little more than a relatively thin layer sitting atop an ocean that is rapidly collecting atmospheric heat. A context that can result in rather dramatic consequences. In short, what this means is that northern polar ice sheet inertia isn’t quite so strong as was previously hoped.

A warming ocean eats away at the bottom ice. And as the thin, frozen ice layer of white, reflective ice is, at first gradually, and then more rapidly, replaced by dark, absorptive ocean the Arctic refrigerator breaks down and, increasingly, turns into a heat amplifier. A quickening pace of albedo loss means an even more rapid pace of warming for the ocean waters below. As warmth concentrates, more feedbacks come into play. Greenhouse gasses like methane and CO2 become liberated from the ice and also go to work in setting off warming. These feedbacks work in concert and, for a time, the Arctic heat rapidly amplifies.

Arctic heat amplification is now plainly visible in winter months when heat absorbed by a mostly ice-free Arctic Ocean during summer radiates up through thin and crack-riddled ice. In this way, heat bubbling up through the ice displaces cold, Arctic air southward, sparking off severe weather. An ongoing event that was particularly extreme during the winters of 2012-2013 and 2013-2014 when Arctic air first fled south over Europe and then the central and eastern United States (see polar vortex collapse).

An extended period of heat amplification has been the story of Arctic warming ever since the world began to heat up during the 1880s. A more moderate spurt of sea ice loss coincided with the growing Arctic warmth from the 1920s to the 1950s before stalling in the 60s and 70s, only to resume with a vengeance during the 1980s. Today, the extreme of Arctic heat amplification results in a number of rather severe knock-on effects that threatens everything from even larger Arctic greenhouse gas releases (methane, CO2) and severe changes to the Jet Stream that may well wreck the periods of relatively stable weather human beings in the north have been used to for 10,000 years running.

Antarctic — Vast Continental Ice Sheets Surrounded By Oceans

Moving southward into the still frozen austral regions, we find a geography and related pace of climate change that is markedly different. Here the vast glaciers pile atop a Continent that has now been buried and frozen for millions and millions of years. The cold is locked into ice sheets that reach thousands of feet in height, cover an area of nearly 14 million square kilometers, and plunge deep into the long-frozen Earth. If the ice in the Arctic is merely a thin facade covering warmer oceans, the Antarctic ice is a thick fortress atop adamant and frozen earth.

The degree of inertia this represents for human-caused climate change is, therefore, much greater than what we see up north. And though the Antarctic fortress is far from impenetrable to the radically strong assaults of human warming, it will resist their insults for longer, giving way its great piles of ice in a more ablative fashion with, likely, even more stark and shocking results.

This densely frozen geography coming into conflict with human-caused warming has resulted in far-reaching, though less visible, impacts. Overall, largely due to the heat-insulation effect of Antarctica, southern hemisphere warming has progressed far more slowly than warming in the north. Here the battle is one of inches in which regions closer to the equator, such as Australia and the equatorial oceans, show the highest rates of warming. Meanwhile, Antarctica has remained, for the most part, a bastion of cold with increasingly intense wind fields isolating it from the more rapidly warming regions. In this case, and in contrast to the Northern Hemisphere Jet Stream, the upper level winds surrounding the South Pole have strengthened even as they have slowly receded.

Antarctica summer storms

(Antarctica surrounded by storms on March 2 of 2014 as a combination of austral summer and human warming shove the Southern Hemisphere Jet Stream toward the pole. Image source: Lance-Modis.)

Such a recession resulted in very hot, dry weather for southern Australia as equatorial heat shoved the strong winds and related storms ever southward. Meanwhile, increased rates of evaporation held in check the benefits of equatorial rain expansion into northern regions. Only the occasional challenge to this new, retreating Jet Stream, breaks the pattern of expanding drought in the south with extraordinary precipitation and storm events. And so Australia has suffered a series of worst droughts and fires on record interrupted by brief but very intense rain events over the past decade.

While the vast ice sheets of Antarctica have, so far, served as a buttress against atmospheric warming even as the Jet Stream retreated southward, heat in the ocean again went to work. Though mostly protected by vast and frozen continental lands to the west, the more northerly segment of East Antarctica featured large sections of submerged continents upon which rested immense, sea terminating ice sheets. Some of these great ice sheets had sections submerged hundreds of feet below sea level. And though the surface waters only gradually warmed, deeper down, the story was much different.

The endless calving of Antarctica’s glaciers sends off thousands of ice bergs from the shores of Antarctica each year. This massive calving cools the surface waters near Antarctica through both the melting of these frozen hills and mountains as well as the chilling effect they have on nearby air currents. As such, cold waters continually flow out from Antarctica. But even these waters have been impacted by human caused climate change, grudgingly increasing in temperature over the decades.

Pine Island Glacier Calves into Amundsen Sea

(Pine Island Glacier calves into the Amundsen Sea. A recent study found this large ice sheet was in the first stages of irreversible collapse. Image source: iSTAR-NERC.)

If the cold surface waters surrounding Antarctica have warmed only slowly, the story of the depths is somewhat different. Down-welling warmer and saltier waters contacting the Antarctic Circumpolar Current create a growing pool of warmth extending to the Antarctic Continental Shelf boundary. There, water circulation dynamics cause the warm water in the abyss to up-well even as it contacts the ocean terminating polar ice sheets.

The warm water thus eats away at the undersides of these ice sheets, causing increasing instability in some of the most vulnerable regions of West Antarctica. This heat transfer from the ocean depths has set off a significant erosion in a number of very large ice sheets and is now spurring the massive Pine Island Glacier (PIG) into an unstoppable rush to the sea.

Models Show Antarctic Sea Ice to Rapidly Decline through Mid Century

If Antarctic warming has been more subtle than the explosive heat amplification of northern regions, it is no less ominous. At the very least, it resulted in locking in 1-2 meters of sea level rise through irreversible ice sheet collapse spurred by warm water upwelling and now puts at risk many more meters of eventual increases to follow.

But, at the surface of the waters, despite a period of slowly rising warmth, the buffer zone of Antarctic sea ice has remained somewhat stable since 1979, even showing periods of moderate increase in overall area and extent. As described above, this is in marked contrast to a stunning collapse of Northern Hemisphere sea ice. A contrast that has served as foil for much debate over the ongoing impacts of human warming even as it was exploited as fodder by climate change deniers, when they weren’t out chasing the most recent snowstorm.

seaice.anomaly.antarctic

(Antarctic sea ice area anomaly since 1979 shows a slight increase in overall coverage, primarily due to a counter-trend increase in Ross Sea ice coverage. New studies show Antarctic sea ice is now set to rapidly decline. Image source: Cryosphere Today.)

Looking more closely, though, one finds that the current expansion of Antarctic sea ice may well be very precarious. For of the three embayments containing Antarctic sea ice only one — the Ross Sea — has shown sea ice growth in recent years. The other two have either remained stable or shown slow recession.

Polar researchers had attributed the moderate net expansion of southern sea ice to a combination of increasingly strong winds spreading out Ross ice flows during winter, a freshening of surface waters through the ongoing melt of Antarctica’s ice sheets that increases the melt temperature of ice and thus encourages its formation, and to changes to ocean currents and rates of precipitation. Now, a new study conducted by researchers at the Virginia Institute of Marine Science has found that this relative period of Ross sea ice stability and growth is about to end.

Warmth About to Crash Through Antarctica’s Gates

The various fragile conditions that have conspired to expand Ross Sea ice are now about to collapse under an onrush of increasing temperatures. For according to a new study entitled The Effects of Changing Winds and Temperatures on the Oceanography of the Ross Sea During the 21rst Century high resolution climate models show both increasing temperatures and rapidly melting ice in this critical and climatologically sensitive region under a regime of business as usual fossil fuel emissions.

According to the study’s authors:

We examined the effects of projected changes in atmospheric temperatures and winds on aspects of the ocean circulation likely important to primary production using a high-resolution sea ice–ocean–ice shelf model of the Ross Sea. The modeled summer sea ice concentrations decreased by 56% by 2050 and 78% by 2100.

In short, the bounding Jet Stream, the insulating continental Antarctic ice, and the cold surface waters surrounding the continent can’t keep out an ever increasing level of human-caused warming indefinitely. Over the coming decades this warmth will pulse higher in the region surrounding Antarctica with profound impacts to sea ice, resulting in a more than 50% reduction by 2050 and a 78% reduction by 2100.

The study also found that:

The ice-free season also grew much longer, with the mean day of retreat in 2100 occurring 11 days earlier and the advance occurring 16 days later than now.

In essence, the spring and summer melt season throughout the Antarctic region was shown to extend nearly one month longer than today’s period of melt and warmth. Such an expansion of heat intensity and duration will have profound impacts not only for sea ice, but for land ice and for life in the oceans as well.

Mixing Layers Reduced, Large Phytoplankton Blooms to Follow

Perhaps less visible but somewhat more ominous are ocean changes that are projected as Antarctic sea ice goes into rapid decline. Study authors found that ocean mixing over the region would fall by 12% by 2050 and a remarkable 44% by 2100. This dramatically increased stratification would, at first, result in very large blooms of phytoplankton as the surface waters see far more oxygen and the depths become ever-more deprived. This riot of microbial life may seem a positive development for the Ross Sea. But, if anything, it is a sign of oceanic productive zones moving southward to the polar region.

More ominous is the impact on krill and larger animals dependent on these small swimmers. Sea ice is critical to the survival of many krill species. And with its decline, these marine animals are likely to be negatively impacted.

According to lead author, Dr. Walker Smith:

our results suggest that phytoplankton production will increase and become more diatomaceous. Other components of the Ross Sea food web will likely be severely disrupted, creating significant but unpredictable impacts on the ocean’s most pristine ecosystem.

Links:

The Effects of Changing Winds and Temperatures on the Oceanography of the Ross Sea During the 21rst Century

The Storms of Arctic Warming

Arctic Sea Ice Melt, Methane Release Shows Amplifying Feedbacks to Human-Caused Climate Change

Arctic Heat Wave to Rip Polar Vortex in Half

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

NOAA ESRL

Lance-Modis

NASA

Cryosphere Today

Skeptical Science

PIOMAS

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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