The Melting of Greenland and West Antarctica

Ice is melting at an accelerating pace in Greenland and the Antarctic. You may know all about this. But maybe like me you’re still just catching up on the basics. If so, here’s a quick intro.

If all the ice in Antarctica melted, it would raise the sea by 61 meters! Such mammoth sea level changes do happen:

But it seems they take millennia. In the shorter term, meaning the next century or two, people tend to focus their concern on the West Antarctic Ice Sheet, or WAIS:

If the entire WAIS melted, it would make sea levels rise 4.8 meters. Another region of concern is Greenland: if all the ice there melted, it would cause a global sea level rise of 7.2 meters. This would inundate many of the world’s coastal cities.

Luckily, it seems no reputable glaciologists think the WAIS or Greenland will completely melt in the coming century. But amount of melting of these ice sheets has been a big challenge to predict.

The last International Panel on Climate Change report, back in 2007, took a pretty conservative stance, and assumed these ice sheets would melt at a slow and more or less constant rate until 2100. Their conclusion was that about 75% of sea level rise would be caused by the oceans expanding as they warmed. The melting of small glaciers, ice caps and Greenland would account for most of the rest. The Antarctic, they believed, would actually provide a small net reduction in sea levels, with increases in snowfall more than enough to outweigh the effects of melting. They predicted an overall sea level rise of between 0.18 and 0.59 meters, with most of the uncertainty arising from different assumptions about what the world economy will do.

However, almost as soon as the 4th IPCC report was released, evidence started accumulating that the melting of Greenland and the West Antarctic Ice Sheet were speeding up. For example:



This graph, taken from Skeptical Science, shows Isabella Velicogna’s estimates of the mass of the Greenland ice sheet. Unfiltered data are blue crosses. Data filtered to eliminate seasonal variations are shown as red crosses. The best fit by a quadratic function is shown in green. The data came from the Gravity Recovery and Climate Experiment—or GRACE, for short. This remarkable project uses a pair of satellites to accurately measure small variations from place to place in the Earth’s gravitational field. When ice sheets melt, GRACE can detect it.

The big news, of course, was that the melting is speeding up. Here’s the same sort of graph for Antarctica, again created by Velicogna:



• I. Velicogna, Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE, Geophysical Research Letters, 36 (2009), L19503.

More recently, Eric Rignot et al compared GRACE data to another way of keeping track of these ice sheets:

• Eric Rignot, Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise, Geophysical Research Letters 38, L05503.

Satellites and radio echo soundings measure ice leaving these sheets, while regional atmospheric climate model data can be used to estimate the amount of snow being added. The difference should be the overall loss of ice.

These graphs show Rignot’s results:


Graph a is Greenland, graph b is Antarctica and graph c is the total of both. These graphs show not the amount of ice, but the rate at which the amount of ice is changing, in gigatonnes per year. So, a line sloping down would mean that the ice loss is accelerating at a constant rate.

By fitting a line to satellite and atmospheric data, Rignot’s team found that over the last 18 years, Greenland has been losing an average of 22 gigatonnes more ice each year. Antarctica has been losing an average of 14.5 gigatonnes more each year.

But also note the black versus the red on the top two graphs! The GRACE data is in red. The other approach is in black. They match fairly well, though of course not perfectly.

The upshot? Rignot says:

That ice sheets will dominate future sea level rise is not surprising—they hold a lot more ice mass than mountain glaciers. What is surprising is this increased contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007.

But how much sea level rise, exactly? Opinions still vary. A recent National Academy of Sciences report said at least 0.6 meters by 2100. But this still doesn’t include any melting of Greenland or the Antarctic!

This paper tries to take Greenland and the Antarctic into account:

• S. Jevrejeva, J. C. Moore and A. Grinsted, How will sea level respond to changes in natural and anthropogenic forcings by 2100?, Geophysical Research Letters 37 (2010), L07703.

The authors say their estimates are in line with past sea level responses to temperature change, and they suggest that estimates based on ice and ocean thermal responses alone may be misleading. With six different IPCC scenarios they estimate a sea level rise of 0.6–1.6 meters by 2100, and are confident the rise will be between 0.59 and 1.8 meters.

This paper suggests an upper bound on sea level rise 2 meters per century (if you max out everything) and a more realistic upper bound of 1 meter/century for this century (it could accelerate later):

• W. T. Pfeffer, J. T. Harper and S. O’Neel, Kinematic constraints on glacier contributions to 21st-century sea-level rise, Science 321 (2008), 1340-1343.

So, except for James Hansen, it sounds like most people would agree on an upper bound of about 2 meters of sea level rise by 2100. This is considerably more than the 4th IPCC report: remember, that gave an upper bound of about 0.6 meters.

I guess one moral is: stay tuned for further developments.

Everything you just read here, and more, was put together by the Azimuth Project team:

Sea level rise, Azimuth Library.

I thank everyone who contributed, especially Staffan Liljgeren and Frederik de Roo.

25 Responses to The Melting of Greenland and West Antarctica

  1. Florifulgurator says:

    The Hansen link doesn’t work. I guess you mean his draft paper with M. Sato (cf. e.g. here):

    Deglaciation, disintegration of ice sheets, is nonlinear, spurred by amplifying feedbacks. If warming reaches a level that forces deglaciation, the rate of sea level rise will depend on the doubling time for ice sheet mass loss. Gravity satellite data, although too brief to be conclusive, are consistent with a doubling time of 10 years or less, implying the possibility of multi-meter sea level rise this century.

    • John Baez says:

      Whoops! I fixed the Hansen link, which is not to a paper by Hansen, but rather to a discussion by Pfeiffer about why he wrote that paper arguing for a 2-meter upper bound on sea level rise in the next century: Hansen had argued for 5 meters.

  2. Nathan Urban says:

    The link to “Eric Rignot et al” goes to Rignot’s web page, but maybe it should go to the paper.

  3. Alpha Omega says:

    Two meters or less in the next 90 years doesn’t sound that catastrophic to me. It seems like there’s plenty of time for low-lying populations to adapt. What’s so scary about this?

    • Florifulgurator says:

      Play with the flood maps server. 3 examples of 2m SLR:
      Osaka, Netherlands, Nile delta.

      (The Nile delta is interesting because that’s where Egypt grows most of their food and where most people live – most of Egypt is desert. Complete inundation is not necessary to wreck Nile delta agriculture: Salt water intrusion into ground water is already a problem. Egypt is the world’s largest importer of wheat – but is meanwhile beyond peak oil, so faces diffiulties financing food imports for an 85 million population. Will they starve peacefully?)

    • John Baez says:

      Alpha Omega wrote:

      What’s so scary about this?

      You’ll note I didn’t use words like ‘scary’. First of all, I’m more interested in figuring out what’s going on than in telling people how to feel about it. Second, this post was focused on the sea level rise, not on the effects of the sea level rise.

      Personally I believe the first serious impacts of climate change will be weather-related problems related to increasingly extreme fluctuations in precipitation: floods and droughts. I believe these are already happening.

      That could—and should—be a topic of a long discussion of its own. The impacts of sea level rise could be another long discussion. But here’s what I know so far:

      Worldwide, the NRC Climate Stabilization Targets report estimates that a 0.6 meter sea level rise would displace 3 million people and raise the risk of flood for millions more. Remember, they estimated 0.6 meters sea level rise by 2100 with no melting of Greenland and the Antarctic.

      I don’t know how this figure would change if we changed 0.6 to some plausible higher numbers like 1.2 or 1.8. I would very much like to know! Does anyone out there know studies on this?

      Wikipedia writes:

      Statistical data on the human impact of sea level rise is scarce. A study in the April, 2007 issue of Environment and Urbanization reports that 634 million people live in coastal areas within 30 feet (9.1 m) of sea level. The study also reported that about two thirds of the world’s cities with over five million people are located in these low-lying coastal areas. [...] A sea-level rise of just 400 mm in the Bay of Bengal would put 11 percent of the Bangladesh’s coastal land underwater, creating 7 to 10 million climate refugees.

      According to the UNEP, 1.5 meters in sea level rise would displace 18 million people in Bangladesh:

  4. Lou Grinzo says:

    Thanks for a concise summary of the polar ice situation.

    Alpha Omega: Here’s a hint: Do a little research and find out how many people around the world will have to relocate with a 2-meter sea level rise. Hint: It’s probably a much bigger number than you’re assuming, and finding a welcoming new home for them will be an enormous, and enormously expensive, challenge. Then add in the coastal infrastructure that will be endangered, like the fresh water wells in the southeast US that are already being shut down due to salt water incursion and the NY City sewer system which will no longer work (see the chapter on NYC in Heidi Cullen’s book), just to name two examples. The human cost will be staggering, and the dollar cost of such adaptation measures will create a huge, ongoing climate tax, far more expensive than reducing our emissions now.

  5. Holland says:

    @ Alpha Omega;
    True. If you live in the mountains, it won’t be a problem. And in low lying areas adaptation might be possible as well.

    However, after another 90 years those 2 meters won’t be doubled. They’re more likely to be tripled or quadrupled. Technically it might be possible to deal with that, but economically that won’t be realistic.

    Since the available amount of oil is not enough to satisfy our addiction to it till eternity, we have to find some more sustainable ways to energize our economy anyway. Preventing escalation of icemelt in the mean time, would be a great idea.

    The costs of drastically speeding up a switch to other sources of energy, will be far much lower than postponing the energy problem and ignoring the climate problem. Both have the same source and similar solutions, so the only reason that’s difficult, is the propaganda of Big Oil.

    However, maybe i better don’t give a damn. After that 90 years don’t live anymore anyway. So it’s the problem of our (grand)children, not ours, right?

    • Alpha Omega says:

      Right, it’s difficult to convince a normal self-interested human that things which may or may not happen to other people in 90 years matter enough to change their behavior now. Difficult, as in basically impossible!

      My beliefs on these matters have gone through 4 stages:

      1) unlimited techno-future ahead, no big problems
      2) big problems ahead, but humanity can solve them
      3) big problems ahead aren’t soluble, civilization is doomed
      4) all/none of the above — the future is unknowable so believe whatever makes you happy now

      This blog seems to be mostly people at stage 2, which I can handle. Unfortunately I see a lot of people progressing to stage 3 and getting stuck there, and they seem quite wretched. At stage 3 your beliefs can destroy your life, and you become worse than useless. Meanwhile a lot of powerful and smart people never seem to get beyond stage 1, and I envy them.

      I propose stage 4 for those who feel that the future is going to be some combination of the other 3 — i.e. some dystopian problems, some low-tech partial solutions and some technological game-changers. At stage 4 you can remain happy, flexible and functional without being delusional. To me this is the default human mode, and the other 3 stages are basically pathologies that you need to deprogram yourself away from.

      • Tim van Beek says:

        People who actually get things done, who identify and solve problems, are those who are in your stage 2: Combine the believe that something needs to be done with the confidence that you are able to do something. To me, that’s not pathological.

        • Alpha Omega says:

          Maybe so, I’m just saying that the quasi-religious belief that every problem can be solved by human ingenuity is a modern idea that didn’t exist in the pre-Enlightenment world, and is probably pathological.

        • Tim van Beek says:

          Alpha Omega:

          …the quasi-religious belief that every problem can be solved by human ingenuity is a modern idea that didn’t exist in the pre-Enlightenment world, and is probably pathological.

          I’ve read statements like “when we run out of oil, the free market will make it profitable for people to look for alternatives, they will invent those, problem solved”. I’m very worried that maybe important people think that research is as simple as that, and that the free markets will solve all problems this way. Research just does not work this way, you cannot speed up people’s thinking by paying more money.

          If you are talking about this kind of attitude, I agree with you.

          On the other hand, in my professional life, I have a lot of interactions with people in the middle management of big companies. “Be optimistic” is a necessity in order to survive in these jobs, and in order to get anything done and be effective. The ability to identify the most important problems, the believe that these problems can be solved, and the ability to encourage others to team up and help with solving these problems, are the key to the success of any company.

          It is a delicate balance, taking the problems seriously, while not to lose the optimism that they will be solved eventually.

      • John Baez says:

        Alpha Omega wrote:

        Unfortunately I see a lot of people progressing to stage 3 and getting stuck there, and they seem quite wretched.

        Who do you think is wretched, exactly? I think you should ask them if they’re actually wretched. Perhaps thinking about their beliefs makes you wretched, but that doesn’t mean they are.

        I don’t think ‘believing whatever makes you happy now’ is the best we can aspire to. It’s possible to be happy while trying to understand what’s really going on, even if some nasty stuff is going on. Suppose humanity is doomed: does that mean I should sit around and mope? That’s absurd! I already know that I’m doomed to die and the universe will most likely end in a heat death. Nonetheless, I wake up each morning bursting with enthusiasm. My big problem is that there’s too much fun stuff to do, and not nearly enough time to do it all.

        • Alpha Omega says:

          I’m talking about the hardcore, apocalyptic Malthusian doomer crowd who have given up all hope and are actively rooting for civilization to collapse. Maybe you haven’t come across these people, but they’re out there, and strangely enough quite a few of them have advanced degrees in science. Visit guymcpherson.com for example. Guy is a former biology professor who believes industrial civilization is the root of all evil and must be destroyed. He’s predicting a new Dark Age by 2012 and a new Stone Age by 2025, and thinks this is great news!

        • John Baez says:

          Alpha Omega wrote:

          I’m talking about the hardcore, apocalyptic Malthusian doomer crowd who have given up all hope and are actively rooting for civilization to collapse. Maybe you haven’t come across these people, but they’re out there…

          Yes, I’ve seen them online. For some reason I thought you were talking about people on this blog, but I guess you weren’t.

      • Florifulgurator says:

        I’d say I’m in a modified stage 2:

        2′) big problems ahead, but humanity could solve them.

        They are just too lazy, stupid, scared, greedy, want more babies, etc. etc., whatever.

        Civilization as we know it is possibly doomed. But that’s not the end of the world. Instead that prospect makes the world way more interesting and challenging. I’m actually happy to be alive at this crucial moment in the evolutionary history of hominids and of Life in total.

        It’s just a slight nuisance for me that I had to decide to continue my postponed math studies now, not when I’m 66.

        How do we live with the fact that we are destroying our world? Joanna Macy has advice in her article The Greatest Danger:

        When we open our eyes to what is happening, even when it breaks our hearts, we discover our true size; for our heart, when it breaks open, can hold the whole universe.

  6. ar18 says:

    The melting of the ice caps, like the climate, is chaotic, not linear and unchanging. Twenty years of data is not representative of the last 1000 years of past history or future trends. That is jumping to conclusions instead of scientific inquiry. The Medieval Warming Period lasted 600 years. The Little Ice Age lasted 800 years. Clearly trends are on the order of 100 of years, not 10 or 20. What we are seeing now is the noise, not the trend. For all we know, the Little Ice Age never ended, and we are just experiencing a short reprieve. Afterall, the damage done by the Little Ice Age has yet to be undone by current “global warming”:

    “The cultivation of grapes for wine making was extensive throughout the southern portion of England from about 1100 to around 1300 (Lamb 1965). This represents a northward latitude extension of about 500 km from where grapes are presently [in 2002] grown in France and Germany. Grapes were also grown in the north of France and Germany at this time, areas which even today do not sustain commercial vineyards…vineyards were found at 780 meters above sea level in Germany. Today they are found up to 560 meters. If one assumes a 0.6-0.7ºC change/100 meter vertical excursion, these data imply that the average mean temperature was 1.0-1.4ºC higher than the present…further botanical evidence which suggests a climatic shift to a colder time is the lowering of the tree line by 70 to 300 meters in the Alps (Lamb 1977, p. 436). This observation is supported by the remains of peat deposits and forests at higher elevations than they presently occur. A similar 100-200 meter lowing of the tree line also occurred in Northern Germany.Iceland experienced a 300 meter lowering of the tree line to the present day levels (Lamb 1977, p. 228)” (http://www.grisda.org/origins/10051.htm)

    Sea levels have repeatedly risen and fallen 140 meters four times in the last 400,000 years. This natural cycle is due to the fact that we are in the midst of an Ice Age. We have not exited that Ice Age yet, just because we are experiencing an interglaciation. To blindly assume otherwise that would be jumping to conclusions…again. Ice Ages last an average of 30 million years, not 400,000 years, so/and there is no evidence that we will not enter another round of glaciation, every-bit as long and cold as the last one (Wisconsian).

    • Florifulgurator says:

      Oh no, not the medieval wine thing again! Luckily I have taken precaution and compiled a list of some of the currently northernmost vineyards in Europe (2010) on the Azimuth Project wiki. Some are at an altitude north of Scotland (Orkney islands)…

    • Nathan Urban says:

      The melting of the ice caps, like the climate, is chaotic, not linear and unchanging.

      No one said it’s linear. (That doesn’t mean it’s chaotic, though, at least not on the time scales being discussed here.)

      Twenty years of data is not representative of the last 1000 years of past history or future trends.

      And no one said it’s “representative of the last 1000 years”. The concern is actually that it may not be representative of the last 1000 years. As for future trends, whether the recent rate will be sustained or not has a lot to do with what’s causing it, which is the subject of current research.

      It’s incorrect to claim that one can simply extrapolate a 20 year trend into the future with confidence. But it is also incorrect to claim that a 20 year trend is uninformative about how ice dynamics respond to temperature over century time scales.

      There is a difference here between simple statistical extrapolation (regression) and mechanistic insight. What such trends may tell us about the future ice response to warming is going to depend on observing more than just the melting, but other covariates (such as temperatures), in combination with physical modeling, rather on arguing whether a set of raw data has a trend in it.

      What we are seeing now is the noise, not the trend.

      That’s an assertion, not a conclusion resulting from scientific inquiry.

      For all we know, the Little Ice Age never ended, and we are just experiencing a short reprieve.

      Again, what we know about the climate does not depend on some simple statistical extrapolation of past temperatures. If all we had was a temperature time series, no, we wouldn’t be able to tell whether the present warming is due to a continuation of the LIA recovery, or whether it is due to the enhanced greenhouse effect. But a temperature time series is far from the only piece of information we have. The reason why we say that the current climate is not merely a continuation of the LIA is due to our observations of natural climate forcings, and modes of variability (such as atmosphere-ocean heat transfer), in comparison to the pattern of anthropogenic forcings.

      We have not exited that Ice Age yet, just because we are experiencing an interglaciation. To blindly assume otherwise that would be jumping to conclusions…again.

      It’s not an “assumption”. Whether we enter another glacial period, and when, is a result of physical understanding of the climate system, both theoretical and observational.

      In the absence of the anthropogenic greenhouse effect, we would likely enter another glacial period within tens of thousands of years. This is not really relevant to what people are talking about here, both because we’re talking about shorter time scales, and because the anthropogenic greenhouse effect is not absent.

  7. If acceleration term of polar ice loss is about -36.3 Gt/year2 during the last 18 years, then acceleration of sea level rise due to ice melt should be 0.1 mm/year2 for the same period.

    However, using Global Mean Sea Level Time Series data from the CU Sea Level Research Group it is easy to see there was a deceleration in sea level rise, its magnitude is about the same but its sign is just the opposite: -0.1 mm/year2.

    Therefore there is a deceleration of -0.2 mm/year2 in sea level rise due to factors other than polar ice melt. Do you know how much of it is due to decreasing rate of heat sequestration in the oceans (as opposed to other factors like increasing water storage in dams)?

    • John Baez says:

      I don’t know the answer to your question, since I’m not an expert on this stuff. But here’s what comes to mind.

      I doubt water stored in dams plays a significant role: I think the ocean is too big for that to matter much.

      Here’s something that sounds relevant, from Gavin over at RealClimate:

      Recently, a new preprint with the latest observations (2003 to 2005) has appeared (Lyman et al, hat tip to Climate Science) which shows a decrease in the ocean heat content over those two years, decreasing the magnitude of the long-term trend that had been shown from 1993 to 2003 in previous work (Willis et al, 2004) – from 0.6 W/m2 to about 0.33 W/m2. This has generated a lot of commentary in some circles, but in many cases the full context has not been appreciated.

      [...]

      One problem is that if the ocean has lost heat at the suggested rate, then the thermal expansion part of recent sea level rise should have decreased (i.e. sea level should have dropped). Overall, sea level however has continued to rise unabated according to the altimeter satellites. The only way to reconcile the results would be to have had a sharp compensating increase in freshwater from the ice sheets adding to sea level (from 0.7 mm/yr to 2.9 mm/yr). This is conceivable (though unlikely), but clearly would not be good news!

      So, he seems to be disagreeing with your claim that sea level rise is slowing, but also saying that if Lyman et al are right that the ocean is warming up more slowly now, then ice sheets need to be melting faster to explain the “unabated” sea level rise.

      However, I find this passage fairly confusing, since:

      1) A decrease from 0.6 W/m2 to about 0.33 W/m2. sounds like a decrease in how fast the ocean is warming up, not a “decrease in ocean heat content”.

      2) Saying that “thermal expansion part of recent sea level rise should have decreased” sounds different than saying “sea level should have dropped”.

      In both cases there seems to be a confusion between a quantity and its first time derivative, so maybe Gavin was not explaining things clearly, or maybe I’m just confused. I suspect that another 10 minutes of reading the links could clear this up, but I’m very tired right now.

      If you click on the reference to altimeter satellites you’ll see this graph of sea level rise, which seems to contradict what you are saying:

      So, maybe you should try to reconcile this data with what you’re saying.

      • Well, you can fit a parabola to the UC sea level data and see the acceleration is -0.103 mm/yr2. It means right now (May 2011) rate of sea level rise is 2.18 mm/yr.

        On the other hand if Rignot is right, current polar ice sheet mass loss is about 675 Gt/year. That alone corresponds to a 1.88 mm/yr eustatic sea level rise.

        As GIA correction is +0.3 mm/yr, that leaves nothing to thermosteric rise. But even 0.33 W/m2 input should have caused at least 0.5 mm/yr. And then no glacier melt outside polar ice sheets is taken into account. Error bars, perhaps. Are they large enough?

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