Q: How much can West Antarctica plausibly contribute to sea level rise by 2100?

A. 3 to 5 feet — contributing to an increasingly likely total sea level rise of more than 5 feet by 2100, a rise that will be all but impossible to stop if we don’t sharply reverse CO2 emissions trends within a decade or so.

West Antarctica’s collapsing ice shelves are in the news today.  This post will survey what we now know about this unstable ice sheet and the threat it poses to humanity — or is that the threat humanity poses to it? — if we continue on our current suicidal emissions path.

Antarctic ice bridge collapse

UK Telegraph: Antarctic ice bridge collapse hailed as new sign of global warming&quot

Antarctica is disintegrating much faster than almost anybody imagined.  In 2001, the IPCC “consensus” said neither Greenland nor Antarctica would lose significant mass by 2100. They both already are.  As Penn State climatologist Richard Alley said in March 2006, the ice sheets appear to be shrinking “100 years ahead of schedule.”

A 2007 study found “The current loss of mass from the Amundsen Sea embayment of the West Antarctic ice sheet [WAIS] is equivalent to that from the entire Greenland ice sheet” (see the new survey report Antarctic Climate Change and the Environment draft here).  And WAIS’s 2007’s ice loss was 75% higher than 2006’s (see “The Antarctic ice sheet hits the fan“).

On Saturday, Reuters reported on a major new study on Antarctic ice shelves, “Coastal-Change and Glaciological Map of the Larsen Ice Shelf Area, Antarctica: 1940-2005“:

One Antarctic ice shelf has quickly vanished, another is disappearing and glaciers are melting faster than anyone thought due to climate change, U.S. and British government researchers reported on Friday.

They said the Wordie Ice Shelf, which had been disintegrating since the 1960s, is gone and the northern part of the Larsen Ice Shelf no longer exists. More than 3,200 square miles (8,300 square km) have broken off from the Larsen shelf since 1986.

Climate change is to blame, according to the report from the U.S. Geological Survey and the British Antarctic Survey, available at

“The rapid retreat of glaciers there demonstrates once again the profound effects our planet is already experiencing — more rapidly than previously known — as a consequence of climate change,” U.S. Interior Secretary Ken Salazar said in a statement.

“This continued and often significant glacier retreat is a wakeup call that change is happening … and we need to be prepared,” USGS glaciologist Jane Ferrigno, who led the Antarctica study, said in a statement.

“Antarctica is of special interest because it holds an estimated 91 percent of the Earth’s glacier volume, and change anywhere in the ice sheet poses significant hazards to society,” she said.

In a remarkable example of the accelerating nature of human-caused climate change, the UK Telegraph reports today:

Satellite images have revealed that a 25 mile long strip of ice, which is believed to have pinned the Wilkins Ice Shelf in place since the beginning of recorded history, had broken at its narrowest point.

Without it, ice will be able to flow more freely between Charcot and Latady islands on the western side of the Antarctic, eventually moving into the open seas.

The Wilkins, the size of Jamaica or half the size of Scotland, is the largest of 10 shelves to have shrunk or collapsed in recent years on the Antarctic Peninsula amid rising temperatures in the region.

You can see a video of the demise here.

The ice shelf has lost a total of 694 square miles – or some 14 per cent of its size – over the past year, which shrank the ice bridge to under 546 yards as its narrowest point….

Ice shelves, some of them hundreds of miles thick [wide], float on the water and contract as they melt, so breakages will not directly raise sea levels.

However, research has shown that when ice shelves are removed, the glaciers and landed ice behind them start to move towards the ocean more rapidly, which will add to the amount of water in the seas.

Antarctic temperatures have risen by up to about 3 Celsius (5.4 Fahrenheit) in the past 50 years, the fastest increase in the southern hemisphere [see “Antarctica has warmed significantly over past 50 years, revisited“].

It is really the warming of the West Antarctic Ice Sheet (WAIS) that you should worry about (at least for this century) because it’s going to disintegrate long before the East Antarctic Ice Sheet does “” since WAIS appears to be melting from underneath (i.e. the water is warming, too), and since, as I wrote in the “high water” part of my book, the WAIS is inherently less stable:

Perhaps the most important, and worrisome, fact about the WAIS is that it is fundamentally far less stable than the Greenland ice sheet because most of it is grounded far below sea level. The WAIS rests on bedrock as deep as two kilometers underwater. One 2004 NASA-led study found that most of the glaciers they were studying “flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates, providing exit routes for ice from further inland if ice-sheet collapse is under way.” A 2002 study in Science examined the underwater grounding lines-the points where the ice starts floating. Using satellites, the researchers determined that “bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed.” And that melt rate is positively correlated with ocean temperature.

The warmer it gets, the more unstable WAIS outlet glaciers will become. Since so much of the ice sheet is grounded underwater, rising sea levels may have the effect of lifting the sheets, allowing more-and increasingly warmer-water underneath it, leading to further bottom melting, more ice shelf disintegration, accelerated glacial flow, and further sea level rise, and so on and on, another vicious cycle. The combination of global warming and accelerating sea level rise from Greenland could be the trigger for catastrophic collapse in the WAIS (see, for instance, here).

You can read every thing a laymen could possibly want to know about what the recent study on Antarctic warming does and doesn’t show at RealClimate here. Andy Revkin blogs on the NYT coverage of the study with expert commentary here.

Now a couple of new papers published by Nature in March have been portrayed as suggesting the WAIS as a whole may be stabler than was previously thought.  Yet the first paper, “Obliquity-paced Pliocene West Antarctic ice sheet oscillations” (subs. req’), concludes:

Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to
3 °C warmer than today and atmospheric CO2 concentration was as high as 400 p.p.m.v.

We’ll be at 400 ppm by 2020.  We’re on track to be more than 5°C warmer by 2100.  So the first paper doesn’t seem terribly reassuring.

The second paper by Pollard and DeConto (the one that got all the attention), “Modelling West Antarctic ice sheet growth and collapse through the past five million years,” (subs. req’), notes, “Recent melt rates under small Antarctic ice shelves are inferred to be increasing dramatically” and concluded:

the WAIS will begin to collapse when nearby ocean temperatures warm by roughly 5 °C. Global climate and regional ocean modelling is needed to predict when and if future ocean temperatures and melt rates under the major Antarctic ice shelves will increase by these amounts, and if so, for how long.

Are you reassured yet?

I would note that West Antarctica land temperatures have risen up to 3°C over the past 50 years — some 4 times what the planet as a whole has warmed. And both Hadley and MIT say the planet will warm more than 5°C by 2100, with a 10% chance of warming more than 7°C (see M.I.T. doubles its projection of global warming by 2100 to 5.1°C and “Hadley Center warns of “Catastrophic” 5-7°C warming by 2100 on current emissions path.  And while the ocean warms less than the nearby land, the new study Antarctic Climate Change and the Environment warns: “UP TO one-third of all Antarctic sea ice is likely to melt by the end of the century.”  So we may yet see polar amplifacation near the South Pole (see “What exactly is polar amplification and why does it matter?“).

Dr. Robert Bindschadler of NASA, who has been an active Antarctic field researcher for the past 25 years, commented on the new study (here):

I’m familiar with the Pollard/DeConto work. They previewed it last fall at an annual science workshop I organize on West Antarctic research. Their model lacks the detail to get the fastest dynamic responses, so the 0.5m/century rate for sea level rise should only be viewed as a lower bound (and a poor one, at that).

Their model is better at getting the longer-term quasi-equilibrium response (it just takes their model a little longer to get there), so it ‘s very interesting that they demonstrate the sensitivity to the ocean temperature. That thinking is certainly where Antarctic scientists are being led by both data and models.

Moreover, the entire WAIS need not collapse for it to contribute to catastrophic sea level rise this century.

The Antarctic Peninsula alone contains “a total volume of 95,200 km3 (equivalent to 242 mm of sea-level; Pritchard and Vaughan, 2007), roughly half that of all glaciers and ice caps outside of either Greenland or Antarctica” (see Chapter 5 here)  — that would be more than 9 inches of sea level rise from a region of WAIS losing its protective ice shelves on both sides at an alarming pace.

But it is westernmost part of WAIS, that borders on the Amundsen Sea, that may be the most worrisome, as AP reported this year:

Glaciers in Antarctica are melting faster and across a much wider area than previously thought, a development that threatens to raise sea levels worldwide and force millions of people to flee low-lying areas, scientists said Wednesday.

Researchers once believed that the melting was limited to the Antarctic Peninsula, a narrow tongue of land pointing toward South America. But satellite data and automated weather stations now indicate it is more widespread.

The melting “also extends all the way down to what is called west Antarctica,” said Colin Summerhayes, executive director of the Britain-based Scientific Committee on Antarctic Research.

“That’s unusual and unexpected,” he told the Associated Press in an interview.

By the end of the century, the accelerated melting could cause sea levels to climb by 3 to 5 feet “” levels substantially higher than predicted by a major scientific group just two years ago.

Making matters worse, scientists said, the ice shelves that hold the glaciers back from the sea are also weakening.

The report Wednesday from Geneva was a broad summary of two years of research by scientists from 60 countries. Some of the findings were released in earlier reports….

The biggest of the western glaciers, the Pine Island Glacier, is moving 40% faster than it was in the 1970s, discharging water and ice more rapidly into the ocean, said Summerhayes, a member of International Polar Year’s steering committee.

The Smith Glacier, also in west Antarctica, is moving 83% faster than in 1992, he said.

The glaciers are slipping into the sea faster because the floating ice shelf that would normally stop them “” usually 650 to 980 feet thick “” is melting. And the glaciers’ discharge is making a significant contribution to increasing sea levels.

So we have the serious potential for 3 to 5 feet of sea level rise just from WAIS this century — and that is on top of whatever we get from thermal expansion of the ocean and Greenland.  And on top of whatever we get from the melting of the inland glaciers, whose contribution was recently increased:

New research published this month in the journal Geophysical Research Letters found that melting glaciers will add at least 7 inches to the world’s sea level “” and that’s if carbon dioxide pollution is quickly capped and then reduced.

Far more likely is an increase of at least 15 inches and probably more just from melting glaciers, the journal said.

So it increasingly looks like we are facing a very serious risk of more than 5 feet of total sea level rise by 2100 on our current emissions path.

But this is almost not news anymore — see Startling new sea level rise research: “Most likely” 0.8 to 2.0 meters by 2100. Indeed, an important Science article from 2007 used empirical data from last century to project that sea levels could be up to 5 feet higher in 2100 and rising 6 inches a decade (see Inundated with Information on Sea Level Rise.  Another 2007 study from Nature Geoscience came to the same conclusion (see “Sea levels may rise 5 feet by 2100“). Leading experts in the field have a similar view (see “Amazing AP article on sea level rise” and “Report from AGU meeting: One meter sea level rise by 2100 “very likely” even if warming stops?“).  Even a major report signed off on by the Bush administration itself was forced to concede that the IPCC numbers are simply too out of date to be quoted anymore (see US Geological Survey stunner: Sea-level rise in 2100 will likely “substantially exceed” IPCC projections).

Did I mention the time to act is now!

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34 Responses to Q: How much can West Antarctica plausibly contribute to sea level rise by 2100?

  1. David B. Benson says:

    Obvious the ice cannot be hundreds of kilometers thick. Should be wdie.

    Pine Island and Thalles glaciers are especially worrisome as both are speeding up, lack much buttressing and extend belonw sea level. Somewhere I read a comment by a glaciologist the this pair of glaciers alone could contribute 1.5 meters of SLR, with much of that by 2050 CE, only forty years away.

    [JR: Pine Island drains into Amundsen sea — so yes, it is part of the 3 to 5 feet SLR.]

    The issue for all of Antarctica proper (I don’t know about the Ppennisula) is the sea water temperatures; the air is almost always cold enough not to cause melting.

    Greenland is less stable than you seem to think; once breakup extends far enough island Greenalnd itself is below sea level so it is possible that the ice sheet could collapse much faster at that time. I’ve only seen speculation about this facet.

  2. paulm says:

    Were facing more than just a risk of >5ft.

    The impression one has is that this is going to be a gradual increase.

    Well it won’t be. There will be sudden increase over short periods as the ice breaks up. And this might start sooner than we think.

  3. Robert says:

    Psychologically, 3 to 5 feet SLR will not be enough to worry most people. The average person will be dead in about 50 years and, unless they live in Bangladesh, Florida or Beijing, probably think they won’t be affected.

    I’m not trying to dismiss the importance, just explain the apathy. Also – why focus on 2100? Under BAU climate change is just getting into its stride and the effects get far worse in the centuries that follow.

    Engaging the current generation in problems that affect later generations (and people in the poorer parts of the world) is the biggest challenge. In An Inconvenient Truth Al Gore describes climate change as a moral issue, although he does not explain why. I think this is the reason.

    [JR: 3 to 5 feet is just the SLR from the WAIS. 2100 is the standard projection date — but I should add a note that it will be all but impossible to stop such sea level rise if we don’t sharply reverse emissions trends within a decade or so.]

  4. Harrier says:

    And for all this I can’t help but feel that sea level rise will be among the least of our troubles. I’m more worried about droughts and desertification, because that starts to cut into our ability to grow food.

    [JR: Lots of coastal land is used for crops — and don’t forget salt water infiltration. And 100,000,000 refugees have to flee to somewhere. I’d equate SLR and desertification about as worrisome.]

  5. Gail says:

    What me worry? It’s all connected. Much food is grown in fertile river deltas that, even if not inundated by rising seas, will have salt water pollute the ground water in agricultural lands.

    Change is never linear. I compare it to my wrinkles. I will go along more or less the same for several years and then suddenly, I notice I look frighteningly more like my mother!

  6. Wonhyo says:

    I’m realizing for most people Greenland, the Arctic, and Antarctica are just too abstract to intrude on their reality. I’ve heard anecdotal evidence of warming effects much closer to home in California.

    One staff member at the Tamarack Cross-Country Ski Resort (sister resort to Mammoth [Downhill] Ski Resort) reports changes in recent years. Mosquitos, which used to be confined to below 10,000 ft elevation are now found at 11,000 ft. Snow used to accumulate at the base of the mountain, at 4,000 feet elevation, but no longer. The mountain pine beetle has been found in recent years, and is devastating the Lodgepole Pine population.

    Tamarack and Mammoth Resorts are in the Eastern Sierra, which supplies much of the fresh water supply for Central California farming and for drinking water in Southern California. My backpacking trips through the Sierras show how much plant and animal life is supported by the year round water supply of the Sierras (in the form of glaciers and snow pack). My drives through the desert to get to these trips show just how dependent we are on the Sierras. If the Sierra snow pack were to disappear, we would have alternating flooding and drought in the valleys below.

    To help get current climate change effects on people’s minds, we need to spend a little more effort on reporting changes that are closer to people’s lives.

  7. Gail says:

    Wonhyo, I so agree.

    It amazes me how blind people are to what is happening right before their very eyes. I have tried to point out to many individuals current deleterious effects of climate change, and other than rare exceptions, I get a blank stare or collective shrug in response.

    I think it is because, to follow the evidence to its logical result, is utterly devastating.

    Rather than do so, the vast majority choose blindness.

    This will only work for so long, however. And soon, we will all have to reflect on the consequences of our profligate squandering of fossil fuels.

  8. DavidCOG says:


    Not sure if you’re aware, but the Telegraph has a strong history of ACC denial, e.g. – and they’re still at it

    It would be nice to see them not get any traffic from the climate realists (or anywhere else!).

  9. Wonhyo says:

    Gail, you’re so right. I find even those sophisticated enough to acknowledge climate change on a global scale find it hard to connect the global changes to local impacts. If people really understood that global climate changes means local food and water shortages, would people really go on with life as usual, without taking concrete steps toward climate action?

    We need more grassroots activism, covering portions of the population that intellectual sites like Climate Progress don’t easily reach. I’ve started introducing climate change and energy issues as part of the “Earth Stewardship” ministry at my church. I think we need to get the religious institutions on board the climate progress movement (before it is completely hijacked by the Religious[ly denialist] Right). There is a large portion of our population that may never “get” the science, but will follow the direction of their religious leaders.

    I don’t often introduce religious language into my climate/energy activism, but from a religious point of view, the ability to understand our impacts (and produce working solutions) through science is a gift from God, and we are compelled to use these gifts in our stewardship of God’s Kingdom. [Translate to the language of any religion, and I believe the resulting imperative will be the same.]

  10. Wonhyo…

    You bring up some interesting points, and I’d like to hear more about how your work is going… I’m wondering how best to reach religious men and women so that more will join the climate change movement because I think that’s one of the few ways we might reach people who typically vote Republican (with apologies for that huge generalization). It would be nice to bring some progressive conservatives into the debate.

    I’ve been planning to get in touch with Stop Climate Chaos Coalition after noting that a serious piece of climate legislation is expected to be passed in Scotland. And I’m wondering if this could be due to the fact that environmental groups and religious groups are working together in common purpose.

  11. Joy Rider says:

    After looking at the MONTHLY average sea ice trends on the NSIDC website… my curiosity got to me about the published percentage of growth or shrinkage of sea ice at the poles.

    The monthly trend graph as of March 31 shows that the Arctic is shrinking at a rate of -2.7% per decade, and now the Antarctic growing at the rate of +4.7% per decade.

    I imported the actual published data tables used for the NSIDC graphs. There are about 350 data points for the nearly 30 years of monthly averages of each type of ice trend: Arctic Extent, Arctic Area, Antarctic Extent, Antarctic Area.

    Unless my spreadsheet and trend graphs are radically incorrect because of some typo or bad import of their data, I got different results from their graphs.

    First off, the GLOBAL averages over all 12 months of the year are as follows:

    Extent: 15.05 million sq. kilometers (both poles averaged)
    Area: 18.55 million square kilometers

    But in graphing the trends, I got even more curious results that show a definite 30-year downward trend in global sea ice since the 1979 satellite data commenced, as follows:

    Global Ice Area decline of 4.3 % in the last 30 years (1.4 % per decade)
    Global Ice Extent decline of 3.3 % in 30 years (1.1 % per decade)

    This included the 2006-2007 minimums in the averages, which did impact the trend. Obviously this does not include thickness.

    What does this mean if my numbers are correct? It means that if the climate trend continues, it will take around 750 to 900 years or so for the poles to be ice free assuming the entire globe heats up for the next millenium. But somehow, I don’t think this is gonna happen considering natural cycles of little ice ages that occur from time to time. And of course, the south pole has been trending up almost constantly. Why don’t you look at the ice GAINS in Antarctica, and even the recovery at the Arctic which is still going on in March, unexpectedly.

    News flash: the past couple weeks Utah added another 12 feet of snow to the mountains! Wow!

  12. Wonhyo says:

    Richard – Can I get in touch with you through the contact email address at the Web page your comments link to? If not, perhaps the Climate Progress Web admin can help us exchange emails privately.

    My efforts at my church are in their nascency. As with many churches, my church membership is declining. I offered climate issues as a way to return the Church to social relevance. This coincided with my church’s decision to create an Earth Stewardship Group. Surprisingly, my pastor (and previous two pastors over 10 years) are very sophisticated in their views of climate/energy and spirituality, but limited in what they can preach from the pulpit. I am successful in engaging several senior church members in an on-going discussion of climate and energy issues. Bottom line is, it will take a grassroots effort to engage the Church in the climate/energy discussion.

    Predictably, there are a few vocal deniers, but I’m encouraged to receive more encouragement than denial. If my church is any example, it will just take some initiative to start an on-going dialogue on spirituality and climate progress. It’s taking a lot of work, but the potential payoff in preaching to the [church] choir is very promising, as people like JR are already doing a great job at preaching to the secular choir.

    Climate Progress: Please send RL my email address.

  13. Wonhyo…

    Sure, you can reach me there… That would be great!

    And Joy… That’s a laughably bad analysis. I think you’re just trying to put us on!

  14. Gail says:

    Along this theme, Wonyo and Richard… JoeR, is there some way since you are revamping up the blog anyway, that those of us commenters and readers can have exchanges more easily? I spend too much time revisiting old posts to see responses to my comments and answer them, and find myself keeping track of the number of replies to see if I should scroll down to read a new one…

    It’s just a bit cumbersome, and I am not website or blog savvy, but perhaps you know of a better and more efficient way for your readers to relate?

  15. David B. Benson says:

    Joy Rider — Globe will certainly heat up for a millennium (and more), but not linearly. Arctic ice will continue to decline, but not linearly. Sea levels will continue to rise, but not linearly.

  16. Harrier says:

    Wonhyo, I would be very interested to see your progress in moving your church to action on climate change. I think the involvement of people of faith could make a serious difference in the fight against climate change. There are certainly religious leaders who understand our dire plight. Case in point:

    If we could move people to change their energy behavior by appealing to their faith, we could work powerful changes. My faith is certainly part of why I want to help combat global warming.

  17. Danny says:

    The responses to this post give me the most cause for hope since I first began reading this blog. As a Florida resident, I often feel that none of my neighbors really cares, at best, or soaks up the Faux News hype and thinks that climate change is a myth (or an excuse to implement socialism). The thing is that for efforts to really have an impact, we have to reach these many millions of people, and bring them on board to demand change. Let’s face it, scientific blogs simply don’t have the influence of talk radio. That’s why I am glad to hear that Wonhyo and others are bringing this to their churches, and that we are finally beginning to reach out to all people everywhere. Let’s hope it works.

  18. ecostew says:

    Very unfortunate that there are those denying the climate science as AGW is intensifying (as evidenced by empirical evidence) and, we are not close to ensuring a sustainable energy future while securing our food and water supplies and protecting the environment – and mitigating AGW. What are Rs thinking!

  19. joyce says:

    Re: churches & climate change
    My brother sent me a good sermon on climate change that the minister gave at his Unitarian church several months ago. I can share.
    Also, we are piloting a science based grassroots effort in our community. The syllabus includes many short videos & interactive sites that can spur discussions.

  20. Harrier says:

    Florida is probably the worst place to be an AGW denier, because it’s going to start going underwater faster than any other place in the country, or even on the North American continent.

    Those deniers are going to be in for one hell of a shock in about three decades.

  21. paulm says:

    Joy , has that snow melted yet?


    you might want to consider very carefully when you decide to sellup in florida. Its not when the SLR start happening but its when everyone realize its going to and suddenly no one wants to buy florida and everyone wants to sell there.

    you have probably 2 – 5 yrs before this happens.

  22. PeterW says:

    Hi Joe,
    Wasn’t there a study in the last year or so that claimed sea-level rise would not rise evenly around the globe at first and it would take time to equalize. I recall something about the Atlantic being more vulnerable to early sea level rise then other parts of the globe. Am I mistaken or have you heard of this study?

    [JR: That is the first of the “related studies.”]

  23. Harrier says:

    Among the limited upsides, we could probably cover a sunken Florida with mangrove trees. We could set up whole new ecosystems.

  24. K Nockels says:

    I just recently watched a stunningly visual NOVA program called Extreme Ice it was a three year time laps study of the Greenland Glaciers. It was the scariest thing I’ve seen yet on the Cryoshere. I could not help but feel that we are walking the edge of the tipping point for Ice on our planet. Once we cross this one all the rest will follow in quick time. For me it is the number of points we are on the verge of crossing, any of which could start a cascade. Gradual is not how the Climate Changes. As Richard Alley puts it, climate lurches it doesn’t glide.

  25. Dan B says:

    Wonhyo, Richard, and anyone else;

    I was on the board of a group that produced a 4 day interfaith environmental festival in Seattle last year.

    It inspired one of the leaders of the Episcopal Church in America to declare his commitment to halving greenhouse emissions in the church in a decade. 500 people stood and cheered.

    If the commitment is profound, or appropriate for the challenge, people will respond.

    Don’t worry if your membership is declining. The moment you assume a prophetic task your ranks will swell. Just make it grand.

  26. Horoscop says:

    god! we have to take action. i guess it’s already late, but we have to do something about it!!

  27. Anonymous says:

    Joe says: [JR: That is the first of the “related studies.”]

    Thanks Joe, I shouldn’t post comments so late at night :-)

  28. Susan says:

    Arctic sea ice thinnest ever going into spring, AP, 4/6/09

    “WASHINGTON – The Arctic is treading on thinner ice than ever before.

    “U.S researchers say that as spring arrives, more than 90 percent of the sea ice in the Arctic is only one or two years old. That makes it thinner and more vulnerable than ever before, according to researchers with NASA and the National Snow and Ice Data Center in Colorado. That is the type of ice that is more likely to melt in the summer.”

    I agree Nova’s Extreme Ice is a must see.

  29. paulm says:

    Susan, should be an interesting summer.

  30. Aaron Lewis says:

    The problem is that none of these ice forecasts are based on models that have been extensively tested and validated by observation. These are “fat tailed” forecasts as discussed in ON MODELING AND INTERPRETING THE ECONOMICS OF CATASTROPHIC CLIMATE CHANGE by Martin L. Weitzman, and at this point we cannot dismiss the uncertainty of the forecasts. Dr. Weitzman says very smart things about environmental data.

    Given the history of climatology, we tend to look down on ice, when in fact the source of heat threatening the WAIS is the ocean at the base of the ice which is hard to see from above. Consider and go back and look at the April sea surface temperature anomalies along the west coast of the Antarctic Peninsula for the last 10 years. What I see is that for the last 10 years that patch of water has been warmer than it was in the previous climate regimes, and this worries me because the difference between salt water that keeps fresh water ice intact; and, salt water that melts fresh water ice is only a fraction of a degree. The WAIS is sitting in thousands of feet of salt water. Despite the support from the water, that ice is highly stressed. If the surrounding salt water warms a fraction of a degree, then the ice is not likely to maintain structural strength, and is likely to collapse.

    I am going out on a limb here and suggest that current models of WAIS overestimate its stability in the same way that models of Arctic sea ice over predicted Arctic sea ice stability just 5 years ago. Those Arctic ice models were off by an order of magnitude. Any risk management model for sea level rise that does not frankly acknowledge that the forecasts of sea level rise may be off by an order of magnitude is merely wishful thinking.

  31. sidd says:

    Re: Pollard (2009) paper, WAIS collapse

    The estimate in the Pollard paper of WAIS collapse after 5C rise in nearby ocean T relies on a modelled estimate by Beckham and Goosse that explicitly excludes ice shelf breakup.

    As the various shelf collapses show, breakup is manifest. So I would not take comfort with the 5C number or the 1000 year timescale. The measured rise of ocean T under the iceshelves now is 0.2 C and they collapse.

    I think Bindschadler is absolutely correct when he says that 1000 yr is an upper limit.

  32. GlobalClimate says:

    This is a great article and something that I don’t think the majority of people are taking serious enough when talking about global warming. If all of these facts weren’t so unknown I think that the world’s leaders would be much more responsive to efforts to help combat climate change. Here’s a short video clip about the story:

  33. Brian Bahnisch says:

    The notion expressed in the linked post that the “West Antarctic ice sheet collapse [will be] even more catastrophic for U.S. coasts” is problematic, I think.

    The UNEP Year Book 2009, Ch 3 says:

    “From the Greenland ice sheet, most of the water would initially stay in the Atlantic. Fifty years after release, sea level rise would be thirty times greater in parts of the North Atlantic, including the gulf of Mexico, than in the Pacific. Similarly, the study found that water from a collapsed Antarctic ice sheet would swamp coastlines in the southern hemisphere, while being barely measurable in the northern hemisphere for at least 50 years (Stammer 2008).”

    The Stammer study is behind the pay wall, but there is a blog post here that does quite nicely.

    The map there shows that the water piles up along the US coastline. bad news for New York, as well as Florida, but the upside is that if New York is threatened the world will act.

  34. Rabid Doomsayer says:

    Irrespective of the actual rise this century, the SLR will continue to increase over the coming centuries.

    If we plan to cope with a 5 meter rise over the next 100 years, then the worst that would happen is that we would be marginally premature. Perhaps we should have contingency plans to cope with a 10 m rise.

    Where new infrastructure has an expected life over 100 years then we really do need to look at the higher levels.

    There are so many unknowns that we are only guessing and the models are so conservative that we are almost certainly guessing low. I am glad that I live 60 meters above sea level.