New Sea Level Study Raises Concerns, Scientists still Counsel Caution

April 4, 2018

Recent headlines somewhat alarming about retreat of Antarctica glaciers.
Having just spent a lot of time interviewing a significant cross section of glacier and ocean experts, (although not the authors of the current study) – I have to raise a bit of caution about immediately going to the “worst case” scenario.

All the experts are deeply concerned about what is happening, all realize that high end, and even moderate, scenarios indicate very serious impacts – but the experts I talked to were cautious and measured in regard to the very high-end, worst case scenarios. Simply put, getting to the higher sea level numbers, especially in this century, entails a lot of assumptions.

Notably, Jonathan Bamber of the University of Bristol was pretty clear that, in his view, a meter was at the upper end of what we can expect in the coming century. (worth noting, sea level rise will not stop in 2100)  Even Eric Rignot, who has made some of the most jaw dropping warnings in recent years, made a point that aggressive decarbonization, and subsequent drawdown (tall order I know) could substantially slow, or even stop, the losses.
Rob DeConto, who has contributed a lot to understanding mechanisms for very rapid ice loss in the past, wanted to clarify that the largest area of uncertainty was not in the ice sheets, but in humanity’s collective decisions about carbon emissions.
That said, clear that trends in sea level projections have been going up in recent decades,  based mostly on better observations. In that sense, the new study is a step forward, and of great concern. Stay tuned.

Inside Climate News:

A new analysis of satellite data has found “extreme” changes underway at eight of Antarctica’s major glaciers, as unusually warm ocean water slips in under their ice shelves.

The warmer water is eating away at the glaciers’ icy grasp on the seafloor. As a result, the grounding line—where the ice last touches bedrock—has been receding by as much as 600 feet per year, a new study shows. Behind the grounding line, the land-based ice then speeds up, increasing the rate of sea level rise.

The new continent-wide measurements of grounding lines suggests a widespread pattern of melting all around Antarctica, said University of Leeds climate researcher Hannes Konrad, lead author of the analysis published today in the scientific journal Nature Geoscience.

Climate models suggest that the current rate of retreat could lead to “centennial-scale collapse of the inland catchment areas,” the study says. That suggests that huge areas of ice far from the ocean could collapse within 100 years, leading to unexpected pulses of sea level rise.

The land-based ice can also speed up in response to ice shelf thinning more than 500 miles away, according to a new study by British and Germanclimate scientists who showed that the effects of localized ice shelf thinning can reach across the entire shelf. Konrad said those findings help show where Antarctica is most vulnerable to future ocean warming, including the large Ross and Filchner-Ronne ice shelves.

Gravity pulls Antarctica’s three-mile thick ice sheet into the ocean along ocean-bottom canyons. The grounding line is where the ice begins to float, and the glaciers and ice sheets turn into ice shelves. When they loosen from the ocean floor, the flow of ice from land accelerates. Ice leaving firm ground and then melting in the oceans causes seas to rise around the world.

From 2010 to 2016, the scientists found that warm ocean water melted 564 square miles of ice from those crucial grounded-ice areas.

Using satellite measurements of ice sheet elevation combined with other factors, like the shape of the seafloor and the known buoyancy of ice, they calculated the grounding lines’ receding rate.

Eight of the frozen continent’s 65 major ice streams had retreated by more than 410 feet per year—five times the average rate of retreat since the end of the last ice age. The grounding line of some of the glaciers emptying into the Amundsen Sea had retreated by up to 600 feet per year.

Fears of Worst-Case Meltdown Scenario

The grounding line retreat reinforces concerns about a worst-case Antarctic meltdown scenario, with global sea level rising 10 feet by 2100. Along with the melting from below caused by warm ocean water, a 2015study showed how global warming is melting ice shelves from above by causing more surface melting. That lets water penetrate deep down into the ice sheets and shelves. When it refreezes, it fractures the ice sheet from within.


Some grounding line retreat is expected in the centuries following an ice age, the researchers wrote, but current levels are far outpacing normal melt rates. Typically, grounding lines should retreat about 82 feet (25 meters) a year, they said. However, some of the studied regions — particularly in western Antarctica — have been receding at up to 600 feet (180 meters) per year. In total, the researchers found that, between 2010 and 2016, warming ocean temperatures melted away about 565 square miles (1,463 square km) of underwater ice from Antarctica — roughly the area of the city of London, England.

The good news is, only about 2 percent of the entire Antarctic grounding line retreated at such high rates, and some parts of the continent aren’t seeing a retreat at all. The bad news is, these if these accelerated rates don’t slow down, they could lead to parts of Antarctica’s inland ice sheet totally collapsing into the ocean. According to a 2017 study, such a collapse would likely put the world on track for experiencing worst-case-scenario sea level rise of 10 feet (3 meters) by 2100.

Further study of Antarctica’s grounding lines is needed to understand why some regions of the continent are receding so drastically while others stand still. According to the researchers, the methods developed for their new study should make future observations of this invisible melting ice much easier.


The greatest declines were seen in west Antarctica. At eight of the ice sheet’s 65 biggest glaciers, the speed of retreat was more than five times the rate of deglaciation since the last ice age. Even in east Antarctica, where some scientists – and many climate deniers – had previously believed ice might be increasing based on surface area, glaciers were at best stable and at worst in retreat when underwater ice was taken into account.

“It should give people more cause for concern,” said Shepherd. “Now that we have mapped the whole edge of the ice sheet, it rules out any chance that parts of Antarctica are advancing. We see retreat in more places and stasis elsewhere. The net effect is that the ice sheet overall is retreating. People can’t say ‘you’ve left a stone unturned’. We’ve looked everywhere now.”

The results could prompt an upward revision of sea-level rise projections. 10 years ago, the main driver was Greenland. More recently, the Antarctic’s estimated contribution has been raised by the Intergovernmental Panel on Climate Change. But its forecasts were based on measurements from the two main west Antarctic glaciers – Thwaites and Pine Island – a sample that provides an overly narrow and conservative view of what is happening when compared with the new research.

The study’s lead author, Hannes Konrad, said there was now clear evidence that the underwater glacial retreat is happening across the ice sheet.

“This retreat has had a huge impact on inland glaciers,” he said, “because releasing them from the sea bed removes friction, causing them to speed up and contribute to global sea level rise.”


On the face of it, the results are pretty much as expected.

Of the 1,463km² of grounded ice that has been given up, most of it is in well documented areas of West Antarctica where warm ocean water is known to be infiltrating the undersides of glaciers to melt them.

Dr Konrad explained: “If you take 25m per year as a threshold, which is sort of the average since the end of the last ice age, and you say anything below this threshold is normal behaviour and anything above it is faster than normal – then in West Antarctica, almost 22% of grounding lines are retreating more rapidly than 25m/yr.

“That’s a statement we can only make now because we have this wider context.”

The new data-set confirms other observations that show the mighty Pine Island Glacier, one of the biggest and fast-flowing glaciers on Earth, and whose grounding line has been in retreat since the 1940s, appears now to have stabilised somewhat.

The line is currently going backwards by only 40m/yr compared with the roughly 1,000m/yr seen in previous studies. This could suggest that ocean melting at the PIG’s base is pausing.

Its next-door neighbour, Thwaites Glacier, on the other hand, is seeing an acceleration in the reversal of its grounding line – from 340m/yr to 420m/yr.

Thwaites is now the glacier of concern because of its potential large contribution to global sea-level rise. And the UK and American authorities will shortly announce a major joint campaign to go and study this ice stream in detail.

Elsewhere on the continent, 10% of marine-terminating glaciers around the Antarctic Peninsula are above the 25m/yr threshold; whereas in East Antarctic, only 3% are.

The significant stand-out in the East is Totten Glacier, whose grounding line is retreating at a rate of 154m/yr.

Overall, for the entire continent, 10.7% of the grounding line retreated faster than 25m/yr, while 1.9% advanced faster than the threshold.

One fascinating number to come out of the study is that grounding lines in general are seen to retreat 110m for every metre of thinning on the fastest flowing glaciers. This relationship will constrain computer models that try to simulate future change on the continent.


18 Responses to “New Sea Level Study Raises Concerns, Scientists still Counsel Caution”

  1. Sir Charles Says:

    After I started reading I was just thinking about your video “Meltwater Pulse 2B”… and there it is. I wonder how long you guys want to stay “cautious”. The red alarm flag should have gone up for long.

    That’s distinct acceleration.

    => 11 alarming facts about sea-level rise

    • L RACINE Says:

      The more extreme predictions are not being fully explored and funded, because of the dire consequence to our way of life if they are found to be valid. Or another way of phrasing it, Don’t go there because nothing good will come from it, if it is that “bad” we a totally screwed, so STFU and keep your “predictions” within the realm of outcomes that our society can manage and deal with.

      The scientist are being manipulated, they are presenting the most cautious and “fact based/defensible” predictions. For them to do anything else will invite censure from their own community, which is understandable given the level of attacks on all of the various fronts, they are defending themselves from.

      Probability multiplied by impact: This means that the total amount of risk exposure is the probability of an unfortunate event occurring, multiplied by the potential impact or damage incurred by the event.

      All I can do is sit here, shake my head and say WTF!!!

      • L RACINE Says:

        One more point, the past predictions on Climate Change by our scientific community is consistently WRONG, without exception have understated the impacts and timing by a HUGE margin. And that in it’s self speaks volumes.

        • greenman3610 Says:

          you are correct, and we are seeing estimates adjusted upward, – but we need to be careful about assuming the very highest projections are therefore automatically accurate.
          see more in my comment below.

      • indy222 Says:

        I mostly agree with you, LRACINE. However, I don’t know if it’s manipulation by their own, but rather manipulation by the wider paymasters in Policy and government. It is entirely true, though, that “nothing good will come of it”, because it seems now pretty clear that global society does not really care about dealing with climate change if it involves economic pain. If we can posture as pro-environmental by putting solar PV on our roof and getting a Prius we’re 100000% for it – AS LONG AS WE SAVE MONEY DOING IT. That’s the fatal key to all this, because Tim Garrett’s work shows that the sum total of all past spending is linearly proportional to the rate of energy consumption in the present. This implies the truth of what I call “Generalized Jevons’ Paradox”, whereby all increasing efficiency savings are merely spent in expanding civilization and thereby expanding its energy consumption rate into the future. So it is SAVINGS that are the enemy of our future. Spending to lower the carbonization of energy is better spending than any other, but it STILL expands civilization and therefore energy consumption, including the carbonized fraction.
        It is excruciatingly true that the IPCC process suppresses investigation and communication of dire findings, because it threatens pro-economic forces. Kevin Anderson is right; we need a long term engineered economic depression if we hope to hold the +2C limit, and that is intolerable. I call on the IPCC scientists to cut their ties to the U.N. and their political and policy reps, and to accept a 95% agreement among its members to then publish. This would neuter the pro-industry folks, the sand in the wheels of scientific truth-telling that has been the result.
        I believe society at large is merely waiting for a hoped for statement from the scientists that it’s now “too late”, and so the anxiety of weighing actions can relax into the irresponsibility enjoying what you can while you still can. And f***k the children, and other species, and their world. Not very inspiring.

        • rhymeswithgoalie Says:

          Aye. There are people who make money by reselling what has been cast off, and this includes combustion buses and cars that have been replaced by EVs, just as once-flooded vehicles WHICH ARE LEGALLY REQUIRED TO BE SCRAPPED end up in the used-car supply.

  2. pendantry Says:

    a meter was at the upper end of what we can expect in the coming century

    A meter? Even that’s going to be pretty damn devastating.

  3. redskylite Says:

    When I first started following your energetic and informative posts (seems many moons ago) all the news was centered around the Arctic, (the Antarctic was assumed fairly stable) – now in just a few years the attention is alarmingly shifting down to the other end of the Earth. What was received as “blockbuster” headlines back then are just received as a matter of fact, everyday “natural” occurrence. It seems it is hard to think in longer time-scales and appreciate where we are heading, especially for all those deniers, lobbyists and profit driven politicians. The most alarming thing is the number of humans who mistake science for politics. Unfortunately (at least in the great U.S of A), the two are intertwined.

    Back to the Arctic and maybe the Antarctic a few years later. This is close to the Green man’s heart.


    The Dark Zone of Greenland ice sheet is a large continuous region on the western flank of the ice sheet; it is some 400 kilometers wide stretching about 100 kilometres up from the margin of the ice.

    Some previous theories have attributed this darkening to water on top of the ice sheet – often seen as strikingly sapphire blue ponds, rivers and lakes. But a new study in Nature Communications provides a new hypothesis based on the character of the impurities on the ice surface itself.

    • greenman3610 Says:

      right, there are two new papers in recent months published by researchers I’ve worked directly with as part of Dark Snow Project – something I’m going to be touching on in this season’s fund raising video coming up soon.
      We’ve been supporting and participating in vital and important research, and a lot of it has been pushing the envelope of what is accepted in the glaciological community.
      So nobody in this enterprise is habitually a shrinking violet in terms of calling things what they are –
      related to some other comments here – while it is critical that we understand how dire our situation is globally, it is equally critical that we don’t get in the habit of taking each paper, and going immediately to the worst-case scenario, and assuming that’s “what the science says” –
      I push back as much on the “game over man” memes as I do on the climate denial memes, and above all, I don’t pretend, as a non-scientist, that it’s ok for me to get out ahead of what the research is telling us, and what the researchers are telling me.
      We have a lot to learn. We may indeed be on the beginning of a new “meltwater pulse” – that would fit the observations – but it could also be that such an event is hundreds of years away – which also would fit the observations – because our era of close antarctic or high arctic data is still short.
      It is also true that there are feedbacks in the system, still being identified, some of which could speed things up, and some which might slow it down – especially if we get a handle on emissions, or even a drawdown.
      We’ll all have more credibility if we are willing to check our assumptions and look objectively at what experts are telling us.

  4. redskylite Says:

    Stunning Drone Video of Sea Ice Reveals Unexpected Climate Change Effects

    As EcoWatch reported in March, the Arctic has just experienced its warmest winter on record. Arctic sea ice also reached its second-lowest extent on record this year, just barely inching out 2017’s ice coverage to avoid being the lowest year for Arctic sea ice ever.

    But according to research published in Geophysical Research Letters on March 15 and cited by Global News, footage like Beyzaei’s is exactly what you can expect from the impacts of climate change on the Arctic.

    The researchers concluded that Arctic sea ice has become more mobile as it has decreased in thickness and extent. It has therefore pushed through channels in the Arctic Ocean such as the Bering and Nares Straits and ended up accumulating more in southern waters than before.

  5. redskylite Says:

    Incredible to learn that the samples collected by Captain Scott’s 1901-1904 Discovery expedition to Antarctica are still intact and still being used in studies of algae.

    The new analysis, published in the European Journal of Phycology, was undertaken by scientists at the Natural History Museum, University of Dundee (UK) and the Brain Chemistry Labs (USA) to evaluate the presence of cyanotoxins – the toxins produced by bacteria called cyanobacteria. The samples were taken at a time when Antarctica which was largely unaffected by human activity, unlike the current landscape which will see drastically altered temperatures affecting the delicate ecosystem in the future.

  6. redskylite Says:

    A bit more from Dr Hannes Konrad in this guest post (Carbon Brief)

    Guest post: Using satellites to track the retreat of Antarctica’s glaciers

    Our results show that most grounding lines across Antarctica are in retreat. This is particularly the case in West Antarctica where 22% of grounding lines are retreating at a faster rate than the average speed when the Earth was emerging from the last ice age (25 metres per year). This compares with 3% of grounding lines in East Antarctica and 10% of those at the Antarctic Peninsula.

    Overall, the continent lost almost 1,500 square kilometres of “grounded” ice between 2010 and 2016. That’s an area the size of Greater London. For the fastest-flowing glaciers, their grounding lines are retreating by around 110 metres for every metre that the glacier thins near the grounding line.

  7. Gingerbaker Says:

    “(worth noting, sea level rise will not stop in 2100)”

    Certainly true! A matter of when, not “if”.

    It’s all well and good to “urge caution” and be conservative. But there are plenty of scientists whose business is to study historical precedents of [GHG] and SLR.

    And, IIRC, they are telling us that SLR is going to be a heck of lot worse than the scientists who make predictions based on contemporary measurements.

    James Hanson is one of the best of those historical scientists, so when he says we are looking at ten feet of SLR by 2070 I’m taking the lower estimates with a big grain of salt.

  8. J4Zonian Says:

    Reputable scientists are always going to be ”cautious and measured in regard to the very high-end, worst case scenarios.” Whether they’re that way by character, or work at it to protect their reputation, they’ve been equally cautious and measured the whole 10 years I’ve been studying climate change nearly full time (independently).

    All that time one cycle has been relentless: Every 2 or 3 years, another study comes out about Greenland ice melt, and every one is accompanied by exactly the same pronouncements by the authors: ”faster than expected”, ”amazing”, ”astounding”, and ”holy shit!” Alternate years are filled with studies about Antarctica, with the same lyrics, and glacial ice studies fill out the odd years. Acceleration like this, accompanied by increasing emissions, increasing feedbacks, decreasing cohesion of civilization, and increasingly autocratic governments uninterested in doing anything except expressing their unconscious rage, means even the most pessimistic scenarios will have to be abandoned as too optimistic. Just like the pessimistic scenarios of the past 30 years.

    To think there’s enough chance this is not going to keep happening that we can ignore it, and pretend we’ll be OK because it might be on the lower end, is insane. To think we can even calculate the accelerating acceleration rate caused by positive feedback loops inside and outside the ice melt is inexcusably naive.

    The only rational response to this certainty/uncertainty paradox is to build clean safe renewable energy infrastructure (and plant forests and transform agriculture) as fast as the world can. Anyone and anything blocking that has to be moved. We cannot let anything else distract us from this, ever.

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