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Making sense of Greenland’s ice

Filed under: — gavin @ 9 July 2007

A widely publicised paper in Science last week discussed the recovery ancient DNA from the base of the Dye-3 ice core (in southern Greenland). This was an impressive technical feat and the DNA recovered may well be the oldest pure DNA ever, dating back maybe half a million years. However much of the press coverage of this paper dwelt not on the positive aspects of the study but on its supposed implications for the stability of the Greenland ice sheet and future sea level rise, something that was not greatly discussed in the paper at all. So why was this?

As we have seen before, the frame for most media reports are set by the press release, and in this case, the press release from the Wellcome Trust (jointly issued by NERC) entitled “Greenland’s ancient forests shed light on stability of ice sheet”. This contained the quote “… this means that the southern Greenland ice cap is more stable than previously thought.” from the lead author Professor Willerslev which ended up being the peg for many of the stories. This quote did not appear in simultaneous releases from AAAS, University of York or the University of Alberta, which were much closer to the text of the paper.

The context for these statements is the uncertainty associated with the history of the Greenland ice sheet – particularly what happened during the last interglacial period (also sometimes called the Eemian) around 125,000 years ago – a time when the orbital configuration lead to Northern Hemisphere summer temperatures being perhaps 1 or 2 deg C warmer than today (and 3 to 5 degrees warmer around Greenland). It is uncontroversial that sea level was then about 4 to 6m higher than present but exactly which ice sheets (Greenland vs. Antarctica) provided this extra water and in what proportion is unclear. The last word on the subject was probably from two papers in Science last year, which suggested that it was roughly half/half with 2m or so from Greenland, and the rest presumably from Antarctica.

Those studies had used as a data point the fact that the Dye 3 core did not appear to have any Eemian ice (unlike ice cores further north), and the minimum Greenland contribution came from a calculation of the minimum amount of ice Greenland would have to lose in order to deglaciate Dye 3. The new data in this weeks paper implies that at least some ice there appears to predate the Eemian (although the dating is uncertain enough so that it can’t be absolutely ruled out), thus the maximum Greenland contribution is likely slightly less than the numbers reported earlier. (Note that all of these estimates are based on ice sheet models, that as we have noted previously, do not fully incorporate all the physics thought to be important).

The University of Copenhagen also issued a release which expanded on the ‘stability’ issue. One of the sections is entitled “Climate theories overturned” and apparently refers to the theory that the whole Greenland ice sheet will melt as a result of global warming. This is a very odd statement indeed and doesn’t accord with any serious discussion of the issue. The authors of the press release must have received some feedback along those lines themselves, because there is an addenda added at the end that gives a bit more context:

The scientists do not want to put into question the rise in sea level during a global warming. During the last interglacial period 125.000 years ago, temperatures in Greenland were 5 degrees higher and global sea level was 4-5 meters higher than it is today. However, since the new scientific results show that the ice sheet also covered southern Greenland, the melting of the Greenlandic ice cap can only have caused a sea level rise of about 2 meters. Therefore some of the ice contributing to the sea level rise must have come from other sources, for instance the Antarctic. Furthermore, thermal warming of the oceans will cause expansion of the sea water and result in a sea level rise of half a meter, and the melting of small glaciers around the globe will result in an additional half meter rise.

This is very similar to the discussion of Eemian sea levels seen in the IPCC report, and so it is very unclear to what extent these new results ‘overturn climate theories’. And of course, the central finding – that southern Greenland was indeed deglaciated at some point in the last half million years – implies that Greenland is indeed unstable – though with a sensitivity that is still uncertain.

So we have, yet again, good science giving rise to bad press coverage, and yet again, it is unfortunately the scientists themselves that appear to have engendered the confusion.


235 Responses to “Making sense of Greenland’s ice”

  1. 151
    Hank Roberts says:

    Lynn, Robinson does a good job on the politics; unfortunately he picked that particular scenario for the first book in his trilogy and the science has changed; a THC slowdown is discussed elsewhere here as likely at ‘worst’ to just slow down heat transport and somewhat reduce the rate of European warming rather than cause a cold event.

    I like Robinson’s books, just finished the third of that trilogy, and have heard him talk locally in SF. He’s making a real effort to understand both the science and the politics; the time line for writing books moves slower than the science news! In the real world, without the fictional sudden THC collapse, the variability of weather and storms and floods he described have rather much happened anyhow, although for other reasons. So has the obfuscation.

    Robinson has a presidential candidate get elected who understands science, after a failed attempt by the administration to steal the next election because some of their team have ethics and defect …. I dunno. We can hope.

  2. 152
    Jim Eager says:

    Re 106 Ryan Stephenson: “Supreme irony don’t you think? Riots caused by proponents of AGW telling us to use less fossil fuel so we burn Mexcian food sources to allow us to use our cars.”

    More like supreme disingenuous and deliberate drive-by smear and mischaracterization on your part.

    The riots were sparked by the sharp increase in corn flour prices, caused by speculators taking advantage of the rising prices of corn stocks used to distill ethanol–from a completely different type of corn, btw.
    http://news.independent.co.uk/world/americas/article2697788.ece

    The surge in ethanol production is due to a Bush administration policy of subsidies to reduce US dependance on imported oil rather than any serious plan to reduce fossil carbon derived greenhouse gasses.

    Moreover, anyone who has seriously looked at biofuels, both ethanol and biodiesel derived from oil seed crops, will tell you that after input and production emissions and land use changes are factored in, biofuels are not at all a carbon neutral solution to AGW.

    You can apologize any time now.

  3. 153
    Hank Roberts says:

    >Mexico
    Heard on the radio yesterday, in the context of the debate over immigration law: Corn that was grown by some 100,000 farmers in Mexico was forced off their market after NAFTA by loss of their tariffs, which led to their market being flooded with much cheaper corn grown in the USA with lots of government crop subsidies; those farms collapsed and those people are now looking for work.

    Tangles: The corn lobby in the USA is huge because of the government-subsidized corn market; corn is subsidized to keep the [economic term for medium exchange deleted to escape spam filter] lower on high fructose corn syrup; that is being used because of the longterm embargo on imports of sugar from Cuba and the tariffs on sugar from other American countries to protect the corn industry. As someone from the left spoke of the wheel put it, well I’ll be ADMned…. those from the right spoke blame it all on Fidel; those from the libertarian and larouchie spokes probably blame the loss of the [generic term for large establishments dedicated to the use of non-random operations to separate medium of exchange from patrons, term edited to escape filter] that were a major feature of Hemingway’s Cuba, but Nevada benefited when those business families moved their operations. You pays your money and you buys your votes. In Mexico and Canada, Coca-cola is made with real sugar from cane; cane sugar doesn’t raise men’s triglycerides the way the high fructose corn syrup does. Here’s to your health.

    But I digress. Sorry.

    What’s news from the Greenland ice cap studies this week, anyone? Anyone gotten hold of the scientists who’ve written the papers, to invite them to comment or expand further?

    Nice topic. Let’s use it.

  4. 154
    Walt Bennett says:

    Re: #79

    Dave,

    You and I agree that regional climate change is the holy grail of climate change knowledge. It is what needs to be understood much better, in order to facilitate prudent policy making.

    One thing that comes to my mind: because we do not completely understand all of the physics involved in distribution of heat from the tropics around the globe, we cannot state with certainty what the impact of a rising temperature will be. As you point out, it is not as simple as “CO2 builds up / the world gets hotter” or as Al Gore is fond of saying, “the planet has a fever”. Because (a) we don’t really know how bad that fever is, in the context of what the likely changes to regional climates will be, and (b) we don’t know what offsetting mechanisms may come into play in order to blunt the full impact of the CO2 increase. In other words, perhaps nature will respond in a way we have not previously observed and which nobody has yet hypothesized (or which somebody has hypothesized and been told they are a crackpot).

    However, I stuck to basics in my answer to Vernon. One thing we know for sure: sea levels will rise. There is the potential that they will rise rapidly when we pass a tipping point. We have seen, many times over, that once a sheet of ice becomes unstable it can disappear at a very rapid rate, i.e. days or weeks. I am fairly certain that this is Dr. Hansen’s primary concern, that there is such a tipping point and that we are close to locking it in.

    I can draw a pretty direct relationship between CO2 buildup and rising sea level. Not only does it exist in the historical record, we can test it and we can model it. I feel quite comfortable that the rapid demise of summer Artic ice cover is directly related to climatic conditions caused by a warming planet.

    I completely agree with you that we must pay much more attention to the specific atmospheric effects which rising temperatures can cause. As I said in my previous post, that answer is much more pertinent to each of us than the gradual rise of “global temperature.”

  5. 155
    James says:

    Re #152: [The riots were sparked by the sharp increase in corn flour prices...]

    Apologies for getting off topic, but I buy corn tortillas & corn meal fairly often. I don’t recall noticing any increase in price here in the US – certainly not a 400% rise – so it seems that there might be more to the story than greedy Americans putting Mexican tortillas in their gas tanks.

  6. 156
    Luke says:

    The wave-cut terraces on San Clemente Island shown in the photo on this page http://pubs.usgs.gov/fs/fs2-00/ illustrate sea level variation up to about 60 metres. The commentary suggests wave-cut terraces and beach deposits from regions as separate as the Caribbean and the North Slope of Alaska suggest higher sea levels. Have there been studies comparing the various wave-cut terraces around the world and do they correlate with various meltwater pulses? Is it possible to identify from a global wave-cut-terrace correlation how different ice sheets might participate in the overall disintegration dynamics, or are there complexities to do with tectonic shifts?

  7. 157
    Hank Roberts says:

    Yes, Luke, you’ll find those with Google Scholar. Some sites have gone back and forth as possible evidence one way or another, for example islands were found to have uplifted or sunk over the same period of time sea level changed, I recall. It’s been discussed here, search box may be helpful too.

  8. 158
    Alex J says:

    We also had this piece that according to another blog contained this:

    During the last interglacial period (130-116 thousand years ago), the climate was 5 Ã�°C warmer than it is today, says Eske Willerslev, director of the centre for ancient genetics at the University of Copenhagen in Denmark. “Sea levels were 5-6 metres higher, and most scientific models have assumed that the melting of the southern Greenland ice cap was responsible. But our data suggest that this was not the case.”

    That comment could easily be interpreted as suggesting that most models have assumed Southern Greenland alone was responsible for that sea level rise. Is that the case, or Willerslev being excessively loose with the language?

  9. 159
    David B. Benson says:

    Re #158: Alex J — Excessively loose, IMHO.

  10. 160
    Philippe Chantreau says:

    Re 155: Agreed. And even if that was the case, we could start by taking high fructose corn syrup out of bread, fruit juice and innumerable other foods where they have no reason to be. Those HFCSs are suspected to play a significant role in children obesity and other health problems. Having a better use for them might save us a tobacco-like fight…

  11. 161
    TotallyScrewed says:

    Hi, everyone! First of all, this is my first post. I am pretty certain that this is the wrong place for this. Although I searched the RC site I could find no mention of ‘Climate change and trace gases’ HANSEN et al. 2007. http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf
    I was looking for this and wondered if there was an idiot’s guide, or at least some kind of critique to help me better understand it?

  12. 162
    Timothy Chase says:

    Climate change and trace gases
    BY James Hansen, Makiko Sato, Pushker Kharecha, Gary Russell, David W. Lea, AND Mark Siddall
    Phil. Trans. R. Soc. A (2007) 365, 1925â??1954
    http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf

    Equation 2.1 on page 1928 reads:

    Fe=1.15[Fa({{CO}_{2}})+1.4Fa({CH}_{4})]

    … but it should be:

    Fe=1.15[Fa({{CO}_{2}})+1.4Fa({CH}_{4})+1.15Fa({N}_{2}O)]

  13. 163
    Vernon says:

    Well, we know that rising sea levels are not due to Antarctic Ice melting or sea ice melting:

    Wingham, et al, Mass balance of the Antarctic ice sheet has found:

    We find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend – growth of 27±29Gtyr^-1 – is based on an assessment of the expected snowfall variability. Mass gains from accumulating snow, particularly on the Antarctic Peninsula and within East Antarctica, exceed the ice dynamic mass loss from West Antarctica. The result exacerbates the difficulty of explaining twentieth century sea-level rise.

    The study went on to add that Antarctic ice build up was actually lowering the sea level by .18 mm per year.

    That brings up the accuracy of the measured sea level. Per Cazenave et al, 2003 the satellite measurement is only within 2-3 cm. To make the readings more accurate they then:

    The tide gauge calibration time series (Figure 6) is used to diagnose problems in the altimeter instrument, the orbits, the measurement corrections, and, ultimately, the final Geophysical Data Records (GDRs). Numerous improvements to the GDRs have been developed in this way and used to produce improved measurements (corrections to the official Geophysical Data Records (GDRs)), which are then recalibrated using the tide gauges.

    How ever using tide gages has problems as can be seen in
    Interannual sea level change at global and regional scales using Jason-1 altimetry http://sealevel.jpl.nasa.gov/science/invest-cazenave.html

    tide gauges have two drawbacks:
    1. their geographical distribution provides very poor sampling of the ocean basins, especially when studying the climatic signal over the past century, and
    2. they measure sea level relative to the land, hence recording vertical crustal motions that may be of the same order of magnitude as the sea level variation. High-precision satellite altimetry, in particular the TOPEX/POSEIDON mission, has demonstrated its capability to monitor sea level variations with great accuracy, high spatio-temporal resolution, global coverage of the oceans, and absolute sea level measurements in a terrestrial reference frame tied to the Earth’s center of mass [see Fu and Cazenave, 2001, for a review]. Analyses of TOPEX/POSEIDON altimetry data indicate that, in terms of global mean, sea level has risen by about two millimetres per year since early 1993 [e.g., Nerem and Mitchum, 2001a, b; Cabanes et al., 2001; see also figure 1].

    Another part of the sea level is the normal oscillation in both the Pacific and Atlantic.

    A significant fraction of this change has also been shown to arise from changes in the Southern Ocean [Cabanes et al., 2001a]. The observations also show a 15-mm rise and fall of mean sea level that accompanied the 1997-1998 El Nino-Southern Oscillation (ENSO) event [Nerem et al., 1999; White et al., 2001].

    So does anyone know where there is a break down of how much the sea level is dropping by melting sea ice, how much it is rising due to Greenland icecap melting, now, how much is due to the various oscillations, PDO or ADO?

  14. 164
    Timothy Chase says:

    PS my post 162

    My mistake.

    Looking at the text more closely, 0.15 in the 1.15 on the outside is supposed to take care of the nitrous oxide. A little odd, though, since nitrous oxide can vary independently of carbon dioxide and methane.

    What is going on there?

    Response: You are confusing two things here. The first is the relative efficacy of the CH4 forcing to the CO2 forcing. Hansen in 2005 showed that for the same radiative forcing, CH4 has ~40% more impact on temperature than CO2 (this is on top of the differences on a per molecule basis). Hence the 1.4 factor. The second issue is that the data for N2O just aren’t as complete as for CH4 and CO2, but a rough calculation of the effect over glacial/interglacial cycles is that N2O adds about 15% to the total forcing. Hence the 1.15 multiplying the CO2+CH4. That’s not ideal since you lose the independent nature of the nitrogen ycle, but is probably the best one can do for the moment. – gavin]

  15. 165
    Hugh says:

    Vernon

    Your link to the Wingham paper appears to be dead.

    Wingham, D.J., Shepherd, A., Muir, A. and Marshall, G.J. 2006.
    “Mass balance of the Antarctic ice sheet. Philosophical Transactions
    of the Royal Society A, 364: 1627-1635.

    New link here:

    http://bowfell.geol.ucl.ac.uk/~lidunka/EPSS-papers/djw3.pdf

  16. 166
    Hank Roberts says:

    Vernon, asking again, what sources are you relying on for the earlier statements you made?

    On the altimetry data, I’d ask the icecap experts if there’s any contradiction in all these reports — seems to me it’s not inconsistent to have observations including
    — more meltwater flowing out at the edges (mass balance studies)
    — more ice varying in surface elevation as water flows under it (the lakes and rivers under the icecap are being found more often and observed)
    — more liquid water and voids under the ice, and more fast-moving water under the ice (look for ‘drumlin’ in Antarctic reports)
    — the top of the ice rising as snow accumulates (the Wingham paper)

    Snow’s light and fluffy for a few years. The ice melting at the bottom is as dense as it gets. I recall ‘icequakes’ occur in Antarctica too.

  17. 167
    sidd says:

    Re: Comment by Vernon 16 Jul 2007 11:40 am

    Thanks for the reference. I note that Wingham arrives at a value of 27+/-29 Gt/yr from data covering 72% of the icesheet for the period 1992-2003.

    This result is to be contrasted with the GRACE results indicating loss for the West Antarctic ice sheet of 148 +/- km^3/yr and the East Antarctic Ice sheet of 0+/-56 km^3/yr for the period 2002-2006. (Velicogna and Wahr, Science 2006). This is disquieting, for it seems that Antarctica has begun melting quickly in the last 5 years.

  18. 168
    Jim Eager says:

    Re 163 Vernon:
    Seems that you are overlooking good old thermal expansion, which I’ve seen up to half of current rise attributed to.

  19. 169
    sidd says:

    Re: Comment by Hank Roberts 16 Jul 2007 1:16 pm
    “Snow’s light and fluffy for a few years. The ice melting at the bottom is as dense as it gets.”

    The values used in the Wingham reference are 0.35g/cc for snow and 0.917g/cc for old ice

    Re: Comment by sidd � 16 Jul 2007 @ 1:52 pm

    I did not include the uncertainty in the WAIS mass loss estimate. Velicogna and Wahr estimate 148+/-21 km^3/yr for WAIS mass loss rate.

  20. 170
    Vernon says:

    RE: 168 Jim, you melt ice on this scale and you get very cold water which takes less volume than the ice did. This would also tend to cool the water as the sea ice melts.

    I ask these things because I have not seen a satellite based study that shows melting in Antarctic and it seems to be the oscillations cause bigger short term sea level change than any thing else.

    So, I again ask, can anyone point me to a study that addresses all the relevant forcings: sea ice melting, occilations, Antarctice ice mass growth, and Greenland Ice mass melting? I would like one that identifies the contribution of each forcing so we can see what the actual trend is.

  21. 171
    Hank Roberts says:

    Vernon, unless you have a subscription, or access to a library where you can read it, most of the current work is behind the subscription wall of _Science_ magazine. You can read the abstracts.

    You may find this one particularly helpful:
    http://www.sciencemag.org/cgi/content/abstract/sci;315/5818/1529

    Science 16 March 2007:
    Vol. 315. no. 5818, pp. 1529 – 1532
    DOI: 10.1126/science.1136776

    Recent Sea-Level Contributions of the Antarctic and Greenland Ice Sheets
    Andrew Shepherd1 and Duncan Wingham

    “… data show that Antarctica and Greenland are each losing mass overall. Our best estimate of their combined imbalance is about 125 gigatons per year of ice, enough to raise sea level by 0.35 millimeters per year. This is only a modest contribution to the present rate of sea-level rise of 3.0 millimeters per year. However, much of the loss from Antarctica and Greenland is the result of the flow of ice to the ocean from ice streams and glaciers, which has accelerated over the past decade. In both continents, there are suspected triggers for the accelerated ice dischargeâ��surface and ocean warming, respectivelyâ��and, over the course of the 21st century, these processes could rapidly counteract the snowfall gains predicted by present coupled climate models.”

    Below is a search for this year’s articles.

    http://scholar.google.com/scholar?hl=en&lr=&safe=off&scoring=r&q=melting+Antarctica&as_ylo=2007&btnG=Search

  22. 172
    Luke says:

    Is there any systematic monitoring / reporting of the ocean floor methane venting being detected by shipping? Apparently hazard alarms are being tripped – eg see http://archives.zinester.com/13183/118372.html Is increased methane venting from the ocean floor to be expected?

    QUOTE: According to U.S. maritime industry sources, tanker captains are reporting an increase in onboard alarms from hazard sensors designed to detect hydrocarbon gas leaks and, specifically, methane leaks. However, the leaks are not emanating from cargo holds or pump rooms but from continental shelves venting increasing amounts of trapped methane into the atmosphere. With rising ocean temperatures, methane is increasingly escaping from deep ocean floors. Methane is also 21 more times capable of trapping heat in the atmosphere than carbon dioxide.

    In fact, one of the major sources for increased methane venting is the Hudson Submarine Canyon, which extends 400 miles into the Atlantic from the New York-New Jersey harbor. Another location experiencing increased venting is the Santa Barbara Channel on the California coast. END-QUOTE

  23. 173
    Aaron Lewis says:

    Re 162 & 164

    Last fall, I seem to remember some anomalously high atmospheric methane measurements at sea level, near leads in the ice over the Sea of Leptev. Now that the ice has melted, has anyone determined the cause of the high readings?

    If it was hydrate decomposition (resulting in the water turnover that caused last springâ��s early melting of the sea ice) then some of this discussion may be – moot.

    If those high atmospheric methane readings were not a result of methane hydrate decomposition, has anyone measured how close various hydrate deposits around the world are to conditions that would trigger their decomposition?

  24. 174
    Hank Roberts says:

    > Maritime …. methane
    The Wayne Madsden link has two followups on his site, but all three articles are behind a pay-to-view wall. I didn’t find any other sources for the info, just that same quote repeated several places (including an armageddon site and a ‘Planet X’ site, so one has to wonder ….)

    I’d think the climatologists might want to inquire of any of the reputable marine gas sensor companies
    (Google Ad Server’s good for something at last!).
    One is: http://www.martek-marine.com

    If they’re doing business, they’re keeping track of false positive alarms on their equipment and thinking about how to adjust if the environmental background of the gas at sea level in harbors actually is changing. The’d have to know the baseline amount.

    Could be it’s just a rumor. Anyone paid the fee to read the original items?

  25. 175
    Timothy Chase says:

    Methane Seeps

    Luke (#172) wrote:

    In fact, one of the major sources for increased methane venting is the Hudson Submarine Canyon, which extends 400 miles into the Atlantic from the New York-New Jersey harbor. Another location experiencing increased venting is the Santa Barbara Channel on the California coast.

    There is a methane seep in the Hudson Submarine Canyon, but you have to go back to 2001 to find any mention of it in credible sources. Everything recent, as far as I can see, has been in blogs and certain radio talkshows.

  26. 176
    Jim Eager says:

    RE: 170 Vernon: “Jim, you melt ice on this scale and you get very cold water which takes less volume than the ice did. This would also tend to cool the water as the sea ice melts.”

    Yes, but that is a regional change. What I meant was thermal expansion of the *entire* ocean as global temperature rises.

  27. 177
    Vernon says:

    I cannot find a study that is not talking about Antarctic sea ice when making claims that the Antarctic is melting. Since we know that sea ice melting does not raise sea levels and based on what we are seeing in the Arctic, may actually lower sea levels, can any one point at a study that actually checks the Antarctic ice cap as Wingham et al did?

    It seems very disingenuous to imply that sea ice melting is causing sea levels to rise.

    [Response: Sea ice melting does cause sea level to rise (only a little though because of the difference in salt content - melted sea ice is fresh water, but displaces salt water which takes up less volume). But Antarctic sea ice is pretty stable for the moment. - gavin]

  28. 178
    Hugh says:

    Vernon

    The Shepherd and Wingham paper that Hank points you to in #171 appears to present a step in the right direction:

    However, much of the loss from Antarctica and Greenland is the result of the flow of ice to the ocean from ice streams and glaciers, which has accelerated over the past decade.

    Nothing about sea ice there.

  29. 179
    Hank Roberts says:

    Yep. Vernon, as I’ve asked repeatedly, _where_ are you getting your information? Wingham’s two papers for example — you got part of one (snowfall in Antarctica) but missed his review of the overall issue. That suggests you’re looking at a secondary source, instead of doing your own research. Seriously, tell us _how_ you’re finding “nothing” and we can help you look better.

    This is _really_helpful:
    How To Ask Questions The Smart Way
    Guide to teach how to ask technical questions in a way more likely to get a satisfactory answer.
    http://www.catb.org/~esr/faqs/smart-questions.html

  30. 180
    Vernon says:

    RE 178: Wingham has the continental ice sheets growing not melting which even with the increased ice flows, he found:

    This range equates to a sea level contribution of K0 -.3�+C0.1 mm yrK1 and so Antarctica has provided, at most, a negligible component of observed sea-level rise.

    So while the Antarctic is currently lowering the sea level, Arctic sea ice melting is doing nothing to the sea level (even counting Gavin’s slight gain due to salinity, it would be pretty close to 0 long term). That only leaves Greenland and the Oscillations, and I have not seen any studies that actually show what the sea level impact is of Oscillations other than the Cazenave et al, 2003.

    The most recent determinations are 1.76 ± 0.55 mm/yr [Douglas, 2001] and 1.84 ± 0.35 mm/yr after correcting for postglacial rebound [Peltier, 2001]. Church et al. [2001] adopt as a best estimate a value of 1.5 ± 0.5 mm/yr and note that the sum of climate-related components is low (0.7 mm/yr) compared to observations. In effect, the observed value is more than twice as large as the revised estimate of the total climate contributions, although there is complete overlap between their respective uncertainties. It thus appears that either the climate-related processes causing sea level rise have been underestimated or the rate of sea level rise observed with tide gauges is in error. Munk [2002] refers to this as ��The Enigma.��

    Which I take to mean that the satellite data indicates a steady trend of just under 2 mm per year where as the tide gages give just under 4 mm per year. There appears to be the assumption that if the satellite data does not support the tide gages, then the satellite data is biased and is being corrected as I addressed in #163.

    So Hugh, what was that question again?

  31. 181
    Jim Eager says:

    Re 180 Vernon: “That only leaves Greenland and the Oscillations”

    Which means you are still ignoring thermal expansion as SST rises.

  32. 182
    Vernon says:

    RE 181: I believe that none of the studies have identified how much thermal expansion there is since the oscillation can cause up to 15mm rise or drop in one year. That is why I am asking if anyone can reference a study that actually addresses all the elements of sea level change.

    From what I have read, the tide gages indicate x amount of sea level rise, but the satellites data does not so it is corrected for this bias with the trend from the tide gages… does this sound familiar?

    There are studies that actually looked that the increase in ice mass in Antarctica that show there is actually a negative impact on sea level rise. There studies that show that the Arctic sea level has been dropping.

    This means that I have not seen a study that actually addresses thermal expansion in light of the other aspects. On, and per the proxy evidence the SST has been dropping for quite a while.

    [Response: Try Ishii et al (poster wcrp.ipsl.jussieu.fr/Workshops/SeaLevel/Posters/3_3_Ishii.pdf ) - long term trends of steric sea level rise are positive. Why do you think that SST proxies show cooling? Try looking at the coral data... - gavin]

  33. 183
    Hank Roberts says:

    Vernon, is either of these websites the source you are trusting for what you believe is science information? Or are you writing there?

    I searched for your belief above and found it on these two pages (and nowhere else). They’re not science sites.

    World Climate Report » Sea Level Rise? – Not From Antarctic Melting
    “Antarctica has provided, at most, a negligible component of observed sea-level rise. …”
    worldclimatereport.com/index.php/2006/12/05/sea-level-rise-not-from-antarctic-melting/

    Signs of the Times Forum / Fire and Ice: The Day After Tomorrow
    “Antarctica has provided, at most, a negligible component of observed sea-level rise …”
    signs-of-the-times.org/signs/forum/viewtopic.php?id=4764

  34. 184
    Hugh says:

    No Hank, through iteration Vernon has come up with something which I am finding very interesting.

    That quote:

    Even allowing a +/- 30 Gt yr fluctuation in unsurveyed areas, they provide a range of 35 +/- 115 Gt yr. This range equates to a sea level contribution of -0.3 +/- 0.1 mm yr and so Antarctica has provided, at most, a negligible component of observed sea-level rise.”

    Is peer-reviewed it’s in the conclusion of the Wingham cite above and here:

    http://bowfell.geol.ucl.ac.uk/~lidunka/EPSS-papers/djw3.pdf

    Vernon, thanks…this is making for really interesting reading.

  35. 185
    Hank Roberts says:

    Hugh, did you read all the way to the Conclusions section of the Wingham cite from 2006? Vernon didn’t give you that.

    They wrote:

    “What is clear, from the data, is that fluctuations in some coastal regions reflect long-term losses of ice mass, whereas fluctuations elsewhere appear to be short-term changes in snowfall. While the latter are bound to fluctuate about the long-term MAR, the former are not, and so the contribution of retreating glaciers will govern the twenty-first century mass balance of the Antarctic ice sheet.”

    Look at the picture in that article. See where there’s loss versus gain?

    And, Hugh, read at least the abstract linked in 171.
    Here, for your convenience:
    http://www.sciencemag.org/cgi/content/abstract/sci;315/5818/1529

    “”… data show that Antarctica and Greenland are each losing mass overall…. However, much of the loss from Antarctica and Greenland is the result of the flow of ice to the ocean from ice streams and glaciers, which has accelerated over the past decade…. over the course of the 21st century, these processes could rapidly counteract the snowfall gains predicted by present coupled climate models.”

    Anything not clear about that?
    Coauthor is the same Dr. Wingham; conclusion is the same as above!

    Science 16 March 2007: Vol. 315. no. 5818, pp. 1529 – 1532
    DOI: 10.1126/science.1136776

    Recent Sea-Level Contributions of the Antarctic and Greenland Ice Sheets
    — Andrew Shepherd and Duncan Wingham

    Don’t trust summaries from World Climate Report (Greening Earth Society/Western Fuels Association/Pat Michaels) — that’s a PR site run by and for the coal lobby.

    Vernon, the Arctic sea level change story is probably coming to you third hand from this news report of one study. At least read the BBC story:
    http://news.bbc.co.uk/2/hi/science/nature/5076322.stm

    You should also look that up in Google Scholar by author name for more.

  36. 186
    Hugh says:

    Thank you Hank, however, what’s going to be the dominant forcing on sea level rise in the 21st century is not what Vernon is asking.

    From my reading of his question he is asking for a summary of contemporary effects which explains the current discrepancy between the estimated rise and the satellite data i.e. the difference between ~2mm/yr and ~4mm/yr (or am I off base here?).

    It seems like a reasonable question considering the fact that this discrepancy has been termed (in 2002) an “enigma”

    http://www.pnas.org/cgi/content/abstract/99/10/6550?ijkey=c398bfa468f139feef6884b2a78ea2fdf31f38e7&keytype2=tf_ipsecsha

    That I have found that the question Vernon asked has led me to undertake some ‘really interesting reading’ and has guided me toward actually reading other resources such as this:

    http://www.ingentaconnect.com/content/klu/10236/2006/00000056/F0020005/00000046?crawler=true

    and this:

    http://www.journals.royalsoc.ac.uk/content/786m1766t6337892/

    and chapter 5.5 of this:

    http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch05.pdf

    …should not be taken as an indication that from here on in I intend to formulate my opinions by reading Pat Michaels, thank you.

    [edited]

    Best Wishes

  37. 187
    Hank Roberts says:

    Good. You’re looking at the same issue Rahmstorff and others have been talking about.

    Vernon wrote above: “Antarctic ice build up was actually lowering the sea level” — but that’s not what the paper said. Sea level isn’t getting lower. As long predicted, there’s more snow in central Antarctica, and if not for that the rate of sea level rise would be slightly greater. It’s already rising faster than anyone expected.

    The “Arctic ocean” studies — two, both using satellites in the absence of any tide gauge data — have huge central blank spots around the North Pole. Something’s up, but they can’t tell what is happening.

    I just worry when people come along and seem to think that sea level is actually falling from misreading the papers.

    Clicking the “citation” button leads to more info, as always.
    Science 4 May 2007:
    Vol. 316. no. 5825, p. 709
    DOI: 10.1126/science.1136843

    Recent Climate Observations Compared to Projections
    Stefan Rahmstorf,1 Anny Cazenave,2 John A. Church,3 James E. Hansen,4 Ralph F. Keeling,5 David E. Parker,6 Richard C. J. Somerville5

    ” … The data available for the period since 1990 raise concerns that the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates.”

    Which brings us back to Greenland, where we have icequakes, outflows from glaciers, and surface melting all increasing.

  38. 188
    Hank Roberts says:

    Thanks, Gavin, for the sea level change poster pointer (#183) — that _is_ good. Reposting, making it clickable: http://wcrp.ipsl.jussieu.fr/Workshops/SeaLevel/Posters/3_3_Ishii.pdf

  39. 189
    Vernon says:

    RE: 187 Hank, read the study which I did quote correctly and it does say that the ice build up in the Antarctic is actually lowering the sea level. Not that the sea level is going down but that the Antarctic is not the source of the sea level rising.

  40. 190
    Steve Bloom says:

    Re #187/8: Hank, there’s been some questioning of sea level trends over at RP Sr.’s in the last few days, so perhaps that’s it.

    There’s also this paper, which appears to be contemporaneous with the poster in #188, plus here’s yet another related poster. I haven’t looked at them carefully to see how they relate. Given the timing, I assume Rahmstorf et al must have taken all of them into account.

  41. 191
    Vernon says:

    Hank, you complain when I don’t list my sources and then when I do, you attribute what I say to something other than the source I reference.

    I never said that sea levels were dropping anywhere but the Arctic, which if you will look at the relevant studies done using satellite based sea level measurement, you will find that the sea level is falling in the Arctic.

    Now I said that the net contribution to sea level rise based on the fore mentioned studies by the Antarctic is negative. That means that if there is no other factors and only the Antarctic, then yes, sea levels would be dropping, but it is not and sea levels are not, and that is not what I said.

    Hugh got it right when he said:

    From my reading of his question he is asking for a summary of contemporary effects which explains the current discrepancy between the estimated rise and the satellite data i.e. the difference between ~2mm/yr and ~4mm/yr (or am I off base here?).

    So, have you found any studies that explain why the ~2mm/yr trend measured by satellites does not match the tide gage measurements. Also, since tide gage measurements are not done world wide but are actually very limited in scope, why they would be used to impose a trend on the satellite measurements?

  42. 192
    kevin rutherford says:

    In light of the discussion about sea levels i’ve recently come across a couple of mentions re Dr Nils Axel Morner from Sweden. He apparently withdrew from IPCC – here’s a taster of what he claims “paleogeophysicist Nils-Axel Mörner, whoâ??s been studying and writing about sea levels for four decades, the scientists working for the IPCC have falsified data and destroyed evidence to incorrectly prove their point”.

    Now I see on google that the usual suspects have embraced him incl larouche & extreme sceptic UK columnist Melanie Philips but that doesn’t necessarily mean he is wrong, though seems very trenchent critisim.

    Not being in a position to really appraise his scientific work etc I was hoping someone here would be able to give a more independent critical assessment of both his claim re sea levels not rising and his outburst re IPCC. Sorry not to provide a cite to any published paper, it was more the general tenet of his argument i was interested in seeing evaluated.

    thanks

  43. 193
    Dan says:

    re: 191. There are several comments re: Morner’s “work” in the responses to comment #1 at http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/index.php?p=97#comment-724

  44. 194
    Hank Roberts says:

    http://www.realclimate.org/index.php?p=314 Sea level in the Arctic

  45. 195
    Hank Roberts says:

    Vernon, I continue to ask you for your sources because you’re saying things without sources.
    If you’ll say what you’re quoting, that’ll help — full cites so people can read the context.
    When you just assert things, you seem to be manufacturing a controversy where none exists.
    Undertainty isn’t unusual in science; there’s no ultimate proof, there are observations to make sense of.

    The variation in the data from tide and satellites isn’t a contradiction or a problem or a weakness — you’re describing how science is put together, from various tools and sources.

    Read here: http://www.realclimate.org/index.php/archives/2007/03/the-ipcc-sea-level-numbers/#more-427
    Look at this: http://www.realclimate.org/images/sealevel_2.jpg
    That chart cites its source: http://www.agu.org/pubs/crossref/2004…/2003RG000139.shtml

    (This is why it’s good to cite sources, so people can look them up. Please do this.)

    There’s one very important word in this abstract: “geocentric” — that probably explains your question.

    “… the geocentric rate of global mean sea level rise over the last decade (1993-2003) is now known to be very accurate, +2.8 ± 0.4 mm/yr, as determined from TOPEX/Poseidon and Jason altimeter measurements, 3.1 mm/yr if the effects of postglacial rebound are removed. This rate is significantly larger than the historical rate of sea level change measured by tide gauges during the past decades (in the range of 1-2 mm/yr)…. questions about whether the rate of 20th century sea level rise, based on poorly distributed historical tide gauges, is really representative of the true global mean. Such a possibility has been the object of an active debate, and the discussion is far from being closed.”

    Science — it just works.

  46. 196
    James says:

    Re #191: [I never said that sea levels were dropping anywhere but the Arctic...]

    Am I missing something here? How can sea levels change in the Arctic, but not elsewhere? Water flows, so I’d think any local change – say a big chunk of Greenland ice falling into the sea – would be felt worldwide within a few days at most.

    Of course you do have a lot of circumpolar land rising due to post-glacial rebound. The denialist camp could try to spin that as a dropping sea level to the general public, but surely you wouldn’t try that here :-)

  47. 197
    Hank Roberts says:

    James, it’s a basin surrounded by land with small connections at sea level, rivers contributing to it, ice, wind patterns and much else, and poorly instrumented. The satellites don’t go exactly over the pole so there’s a big blank area still in the satellite studies. This is all quite new work being figured out. A little searching:

    Observations of Polar Ice With Spaceborne Altimeters: Recent …
    Arctic sea level change from satellite altimetry. * Scharroo, R
    http://www.agu.org/meetings/sm06/sm06-sessions/sm06_G21A.html

    Sea level variability in the Arctic Ocean from AOMIP models
    by Scharroo et al. [2006] based on satellite observations over the entire Arctic Ocean. The sea level time series obtained from this study …
    http://efdl.cims.nyu.edu/project_aomip/publications/jgr_2006/proshutinsky_sealevel.pdf

    Recent Decrease of Sea Level Pressure in the Central Arctic
    JE Walsh, WL Chapman, TL Shy – Journal of Climate – ams.allenpress.com
    … Satellite passive microwave data and/or under ice draft …
    The Northern Hemisphere sea level pressure data …
    http://ams.allenpress.com/amsonline/?request=get-abstract&doi=10.1175%2F1520-0442(1996)009%3C0480:RDOSLP%3E2.0.CO%3B2

    ‘Sea level in the Arctic is falling’
    Answer: Yes, a new study using Europe’s Space Agency’s ERS-2 satellite has determined that over the last 10 years, sea level in the Arctic Ocean has been … http://gristmill.grist.org/story/2006/11/9/162012/366

  48. 198
    Vernon says:

    RE: 196 I think that if you go and read the studies based on satellite measurements, the sea levels the rate of sea levels rising or fall varies from sea to sea. Please do not take my word for it… google it for your self.

  49. 199
    Hank Roberts says:

    This may help for the past century’s info.
    This does _not_ talk about satellite work (see the above for that).

    http://www.journals.royalsoc.ac.uk/content/f6v6775433542251/

    On the rate and causes of twentieth century sea-level rise
    Issue Volume 364, Number 1841 / April 15, 2006
    Pages 805-820
    DOI 10.1098/rsta.2006.1738
    Laury Miller 1, Bruce C. Douglas 2

    1 NESDIS, NOAA Laboratory for Satellite Altimetry Silver Spring, MD 20910-3282, USA
    2 Florida International University Laboratory for Coastal Research Miami, FL 33199, USA

    ——Abstract——-

    Both the rate and causes of twentieth century global sea-level rise (GSLR) have been controversial. Estimates from tide-gauges range from less than one, to more than two millimetre/yr^-1. In contrast, values based on the processes mostly responsible for GSLR – mass increase (from mountain glaciers and the great high latitude ice masses) and volume increase (expansion due to ocean warming) – fall below this range.

    Either the gauge estimates are too high, or one (or both) of the component estimates is too low.

    Gauge estimates of GSLR have been in dispute for several decades because of vertical land movements, especially due to glacial isostatic adjustment (GIA). More recently, the possibility has been raised that coastal tide-gauges measure exaggerated rates of sea-level rise because of localized ocean warming.

    Presented here are two approaches to a resolution of these problems.

    The first is morphological, based on the limiting values of observed trends of twentieth century relative sea-level rise as a function of distance from the centres of the ice loads at last glacial maximum. This observational approach, which does not depend on a geophysical model of GIA, supports values of GSLR near 2mmyr^-1.

    The second approach involves an analysis of long records of tide-gauge and hydrographic (in situ temperature and salinity) observations in the Pacific and Atlantic Oceans. It was found that sea-level trends from tide-gauges, which reflect both mass and volume change, are 2-3 times higher than rates based on hydrographic data which reveal only volume change.

    These results support those studies that put the twentieth century rate near 2mm/yr^-1, thereby indicating that mass increase plays a much larger role than ocean warming in twentieth century GSLR.

    —– END ABSTRACT — [paragraph breaks added for readability -hr]

    Many of the references to the above page are also clickable links.
    Now — Greenland thread? The above covers the past century. What’s happening now that will affect this century?

  50. 200
    Hank Roberts says:

    Vernon, you wrote:
    “go and read the studies…. google it for your self.”

    You keep coming back to the assertion that sea levels in different places must be going up and down.

    It’s a bogus argument being made to claim that the big ice masses like Greenland can’t be melting. You can find _that_ plenty of places on the Internet. Not science. Check the sources.

    This speaks directly to that claim:

    http://www.grdl.noaa.gov/SAT/pubs/papers/2004nature.pdf

    “Concerning the causes of sea level rise, our results provide clear
    evidence that changes in ocean volume due to temperature and
    salinity account for only a fraction of sea level change, and that mass
    change plays a dominant role in twentieth-century GSLR. This
    aspect of our results is consistent with the results of Antonov et al.7,
    who show that the global oceans freshened during the latter half of
    the twentieth century by an amount equivalent to 1.4mm/yr21 of
    fresh water, but goes further by indicating that the source must be
    continental. The only alternative to this interpretation is that what
    we identify as mass change is actually a mass redistribution within
    the global ocean rather than a mass increase due to the addition of
    fresh water. However, for this to be true, large areas of the global
    ocean would have to have falling sea levels for the entire twentieth
    century. Observations from the global tide gauge network, consisting
    mostly of gauge sites located along themargins of the ocean basins, do
    not support this viewpoint. Whether the mid-oceans are currently
    undergoing such changes can only be determined from long-term, high-
    precision satellite altimeter missions, such as the TOPEX/ Poseidon
    and Jason missions, which are at present under way.”

    Just sending people to Google means they find everything, some of it nonsense.

    Who do you consider reliable as the source for what you believe?


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