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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. 1
    gerald spezio says:

    Orwell lives and then some.

  2. 2
    Vernon says:

    Based on UC Irvine study of Artic warming/melting http://today.uci.edu/news/release_detail.asp?key=1621 and the lack of Antarctic warming or melting raises the possiblility that the Greenland Ice sheet, which is miles thick, is less affected by dirty show and water temperatures then was though in the past? Since a significant amount of the Artic warming is due to pollution, not temperate and tropical latitude heating, up to 94 percent according to the UCI study, then would not cleaning up the pollution do away, over time, with Artic warming and melting, therefore stabilizing the Greenland Ice sheet?

    At least this needs to be studied as it is significant to both GCMs and policy decisions.

    [Response: The effect of black carbon on snow is significant and does have a greater effect in the Arctic than elsewhere, but single factor explanations for what we are seeing are inadequate. See Hansen et al (2005) or 2007 for discussions of how that one individual forcing fits in to all the other changes. Going forward, the biggest growth in the warming factors is likely to be CO2, not black carbon, but efforts to reduce BC could certainly help. -gavin]

  3. 3
    Alexander Ac says:

    Obviously, journalists would like to know more, than the research says ;-)

    Was the position of Greenland 125,000 ago the same or similar as of today? As unfortunate I see the statment “more stable than previously though”… but in any case, will the sea level rise be the most serious, we can await from future climate change? Won’t be the precipitation and weather pattern changes more important than that?

    Best,

  4. 4
    Anonymous says:
  5. 5
    Vernon says:

    RE: 2 Gavin, fully understanding that more needed to be done that just the UCI study, what if the high end numbers are correct? If current warming is due to black carbon (94 percent, and I know we cannot be sure of that with out further study) what does that due to the current theory and what impact does that have on current models?

    [Response: But it doesn’t explain global warming at all. Though as I said, attributions based on single factor experiments are not sufficient. For instance, other aerosols provide a cooling effect and so you could easily have CO2 and BC both providing 0.5 deg C of the effect in the Arctic, and the sulphates providing -0.5 deg C for a total of 0.5 deg C warming. Thus CO2 and BC would both provide 100% of the effect! Modelling of each of the factors will no doubt improve, but as of now, BC is a minor player, though non-negligible – but then so are tropospheric ozone, methane, N2O, sulphates, nitrates, solar, volcanics, land use change etc. – gavin]

  6. 6
    Bryan says:

    A little knowledge can be a dangerous thing!
    Having done some work training journalists in science I can tell you their experience and knowledge (even for “scientific/environmental” reporters) can vary wildly..

    that said, I think the naysayers will always find a way to twist anything to suit their needs…

    [Response: This wasn’t an issue with the journalists nor with the naysayers, it is an issue of scientists (and their press offices) using a news peg that was guaranteed to produce confused and inaccurate stories. Journalists and editors can’t be blamed for writing stories that reflect that. – gavin]

  7. 7
    wacki says:

    Hello good readers of Realclimate.org. I have spent a considerable amount of effort documenting the scientific consensus on my website here:

    Logical Science: The Consensus on Climate Change: From Science to Industry & Religion

    As you can see the list is pretty extensive and it’s probably the most definitive list on the web. I have received numerous e-mails recently asking about organizations outside of the US. Obviously there are language barriers that get in my way so I’d appreciate some guidance from RC’s foreign readers. Also, if anyone thinks I’ve missed any important statements I’ve missed (especially from industry) please email me. My email is posted at the bottom of every page on http://www.logicalscience.com.

    Sorry for the hijack Gavin but I’m sure you can agree this is for a good cause!

  8. 8
    Andrew Sipocz says:

    I guess the authors conclusions are based on the idea that the odds the ice core just happened to hit on an ancient glacier or some isolated patch of ice were small enough to disregard and that their results indicate the presence of an ice sheet at least 50% the size of the current one in S. Greenland since they halved the ice sheet’s sea level contribution. Is this valid?

    How did the core drillers choose their site? How good of a picture do scientists have of Greenland’s underlying topography? Was the core purposely placed in a spot likely to hold a continuous record of ice such as a high mountain valley?

    The simultaneous ideas that S. Greenland was both covered by an all encompassing ice sheet and supported a boreal forest seem contradictory to me. Gavin seems to point this out in his quote. I do like the graphic which pictures a mountain and glacier in the background. That makes sense.

    It also reminds me of a nice story published in Wild Earth (now defunct) about the work of scientists studying the preserved insects literally pouring out in the meltwater from a disappearing glacier in Montana. Here is something recent but I’m sure a search of Dr. Lockwood’s work would bring up quite a few publications. Lockwood, J. A., J. C. Burne, L. D. DeBrey, R. A. Nunamaker and R. E. Pfadt. 1990. The preserved fauna of grasshopper glacier (Crazy Mountains, Montana): Unique insights to Acridid biology. Boletin de Sanidad Vegetal 20: 223-236. Dr. Lockwood has studied N.America’s now extinct locust species by examining the grasshoppers which flew or were blown up onto the glacier and preserved until now.

  9. 9
    Todd says:

    The question remains, how much ice remained on Greenland during the Eemian?

  10. 10
    pete best says:

    It is a shame that the article does not expand on the science of the Eemian itself and tell us how much additional heat the orbital configuration of the earth gained to be 1 to 2 degrees C warmer than todays interglacial which created that 6M sea level difference?

    If the northern hemisphere was warmer what would happen to the southern hemisphere and Antartica in particular, would it not be colder there ?

    Were CO2 and other GHG concentrations the same as preindustrial levels 125,000 years ago.

    How long did the Eemian last and was it warmer through the entire phase of that interglacial.

    great post once again RC.

  11. 11
    Andrew Sipocz says:

    I can’t find the reference, but I definitely remember someone describing the Eemian southern Greenland ice cap as a steep dome as they attributed its contribution to the Eemian high sea level stand. Have Gavin, Hansen, Rahmstorf ever described the southern Greenland ice cap as non-existent during the Eemian? Is this simply a case of a molecular biologist making incorrect assumptions on behalf of other scientific disciplines?

    [Response: The reference you refer to is Otto-Bliesner et al (2006): http://www.sciencemag.org/cgi/content/abstract/311/5768/1751 – gavin]

  12. 12
    Sam says:

    RE:11 AR4 indicates that ice sheet models predict complete Greenland melting with 4 times pre-industrial co2 levels sustained for centuries. Maybe someone needs to take a second look at the models.

  13. 13
    Ray Ladbury says:

    Sam,
    Actually, 4x CO2 might well do it. That’s a lot of warming for a fairly long time.

  14. 14
    llewelly says:

    Pete Best:

    Were CO2 and other GHG concentrations the same as preindustrial levels 125,000 years ago.

    Although CO2 levels during most of the Eemian were indeed close to preindustrial levels of about 275 ppmv, the peak of Eemian CO2 levels, at nearly 125 kyr ago, was about 290 ppmv, significantly higher. See globalwarmingarg.com Current CO2 level is about 383 ppmv . (Which I take to mean that if CO2 levels do not come down substantially within the next few centuries, all this argumentation about the extent of GIS melting during the Eemian is argumentation about the wrong example.)

  15. 15
    Bryan says:

    Gavin:
    Thanks for the clarification.
    If it is a case of scientists using the press/news by manipulating their releases, then shame on them, not the press.
    Thanks

  16. 16
    Timothy Chase says:

    Gavin,

    I was hoping that this would be the next topic you would cover. Thank you for granting my wish, especially as I hadn’t mentioned it.

    It sounds like rather than overturning the mainstream view, this result actually just confirms it – namely, the half-and-half between the Western Antarctic Peninsula and Greenland. One point though: I believe I ran across a statement by you that suggested that the study might indicate that Greenland is actually more unstable than it has appeared so far.

    Am I remembering correctly, and if so, what is the reason for this view?

    [Response: Because it does show definite proof that southern Greenland was deglaiciated in the relatively recent past. Previous inferences were indirect. – gavin]

  17. 17
    Vernon says:

    Actually, if sulfates are blocking income radiation and most if not all Arctic warming can be attributed to Black Carbon, then there is nothing to indicate that the warming is due to CO2. This does not go against the physics, since CO2 can only cause warming if the radiation penatrates to the CO2 and the sulfates stop it. This means that CO2 could go to 4 times with out heating the Arctic just as current CO2 increase may not be heating the Arctic.

  18. 18
    Vernon says:

    RE: 14 If the Arctic warms and releases all trapped greenhouse gas, then why when the Arctic melted last and Greenland mostly or completely melted did the CO2 level not go up? Why did the CO2 in the sea not also get release?

  19. 19
    Timothy Chase says:

    gavin (inline to #16) wrote:

    Because it does show definite proof that southern Greenland was deglaiciated in the relatively recent past. Previous inferences were indirect.

    Well, given IPCC recommendations, it looks like we will get our two degrees – and that is assuming we have the political will needed to put into action those recommendations. Plus the problem with carbon soot wasn’t something which we had in the recent past. So this would suggest additional warming. Moreover, I would suspect that in terms of ice dynamics, it isn’t just a question of how much the temperature rises, but how quickly – given the nature of non-linearity involved in glacier melt.

  20. 20
    llewelly says:

    Sam:

    RE:11 AR4 indicates that ice sheet models predict complete Greenland melting with 4 times pre-industrial co2 levels sustained for centuries. Maybe someone needs to take a second look at the models.

    2x pre-industrial CO2 is about 550 ppmv. 4x is about 1100 ppmv . The highest in level in the last 400 kyr was about 310 ppmv . Older CO2 levels are uncertain, but based on this graph , the last time 550 ppmv was exceeded may have been as long ago as the middle Paleogene. As far as I know, there were no ice sheets at the present-day latitudes of Greenland during the Paleogene, but the arrangement of the continents was significantly different. I think this greatly limits how much we can learn about the effects of centuries of 2x CO2 (much less 4x CO2) from paleo-climate studies.

  21. 21
    Hank Roberts says:

    Vernon, you’ve got the direction backward: incoming sunlight penetrates to the ground, the ground radiates in the infrared, and the CO2 slows down the loss of that energy back into space.

    You can tell for sure that the sulfates are not blocking all the incoming radiation, because the sky is bright during the daytime.

  22. 22
    Timothy Chase says:

    Vernon (#17) wrote:

    Actually, if sulfates are blocking income radiation and most if not all Arctic warming can be attributed to Black Carbon, then there is nothing to indicate that the warming is due to CO2. This does not go against the physics, since CO2 can only cause warming if the radiation penatrates to the CO2 and the sulfates stop it. This means that CO2 could go to 4 times with out heating the Arctic just as current CO2 increase may not be heating the Arctic.

    Hansen strongly recommends the reduction in black carbon. Carbon dioxide acts in the stratosphere. Aerosols are an issue principally in the thermosphere – and to counter the effects of increasing levels of carbon dioxide without attempts to curb its growth, we would have to emit a geometrically increasing amount of aerosols, particularly since they tend to be washed out by rain. Carbon dioxide isn’t. And while aerosols have masked the effects of carbon dioxide until quite recently, they aren’t doing so as effectively any more. In addition, aerosols have their own problems associated with them in terms of acid rain, their effects upon the weather, and the associated lung ailments.

    And we have a good estimate of climate sensitivity to carbon dioxide as the result of paleoclimate studies. Roughly 2.9 degrees Celsius per doubling.

  23. 23
    Petro says:

    “This does not go against the physics, since CO2 can only cause warming if the radiation penatrates to the CO2 and the sulfates stop it.”

    Vernon, you are a brave man ready to take all the deserved beating on this most ridiculous argument for long time!

  24. 24

    http://tinyurl.com/329qwz

    Two New Articles Which Document The Limitations Of The Multi-Decadal Global Climate Model Predictions

    I’m not qualified to vet his arguments. Are the models as broken as he indicates?

  25. 25
    Chuck Booth says:

    Re # 18 Two New “Articles”
    According to your source (Roger Pielke Sr. Research Group Weblog):
    “The first new information is in a poster … entitled “Inter-model Climate Sensitivity” by J.T. Kiehl and C.A. Shields. ”

    Be aware that conference posters are not peer-reviewed (even if the abstract is, which is often not the case).

    “… a second article that highlights the overselling of the 2007 IPCC WG1 Report’s statement on the multi-decadal global model predictions…is in Nature Reports Climate Change Published online: 27 June 2007 … in an article by Stephen E. Schwartz, Robert J. Charlson & Henning Rodhe entitled “Quantifying climate change – too rosy a picture?”

    I haven’t read this, but it appears to be a news article rather than a peer-reviewed research article. As with press releases, one has to read such articles with caution, even if they are written by scientists.

  26. 26
    Timothy Chase says:

    Sam (#12) wrote:

    RE:11 AR4 indicates that ice sheet models predict complete Greenland melting with 4 times pre-industrial co2 levels sustained for centuries. Maybe someone needs to take a second look at the models.

    Not what mention of Greenland I have found in the AR4WG1:

    The inferred warming was largest over Eurasia and northern Greenland, whereas the summit of Greenland was simulated to be 2 C to 5 C higher than present. This is consistent with ice sheet modelling suggestions that large-scale retreat of the south Greenland Ice Sheet and other arctic ice fields likely contributed a maximum of 2 to 4 m of sea level rise during the last interglacial, with most of any remainder likely coming from the Antarctic Ice Sheet.

    pg. 435, AR4WG1, Chapter 6

    The way I read this, it is entirely consistent with the analysis given in Gavin’s essay above. Perhaps you have in mind a different passage?

  27. 27
    Vern Johnson says:

    Gavin, the EEmian period, 125,000 years ago is interesting for more than one reason. Genetic studies of the 3 kinds of human body lice reveal that taenia corporis, the body louse of man is very closely related genetically to the chimpanzee head louse, but it attaches only to clothing and not to skin, giving rise to the theory that humans did NOT wear any clothes, even animal skins, at about that same period in history, 125,000 years ago plus or minus. Not necessarily in Greenland of course, but the temperature rise elsewhere may have been more significant causing no thought of clothing and probably further promoting,also the evolutionary loss of much body hair then already underway for millions of years. What do you think of this cognitive anthropological approach to evolutionary theory and how it may also support climate-change models?
    Vern Johnson

  28. 28
    Vernon says:

    RE: 23 Why is this the most ridiculous argument for long time! If black carbon could be responsible for all most all warming and melting in the Arctic, then where is the CO2 based warming? It is not happening in the Antarctic.

    Has anyone considered that maybe we got it wrong. That black carbon is rasing the temps in the Arctic and that is warming the rest of the NH? I don’t really thank so but how about some proof?

  29. 29
    sidd says:

    Re:Comment by Andrew Sipocz â�� 9 Jul 2007 11:01 am amd Gavin’s inline response
    referencing Otto-Bliesner et al., Science 311, pp. 1751-1753

    I see from the reference that the Dye 3 was at the edge of the icesheet in simulation A in Fig. 3 of the reference. So is it not possible that the simulation for LIG is slightly off and that the Dye-3 site was glaciated through the LIG ?

    Further this supports the theory that W. Antarctica contributed substantially to sea level rise in the LIG, although the insolation anomaly was small in the Southern Hemisphere. By contrast, CO2 forcing is not confined to the Northern Hemisphere, so naively I would think the effects this time around will be larger in Antarctica. The other question in my mind is the role of sea level rise and ocean warming in the destabilization of W. Antarctica. As shown by Barnett et al. Science v309, pp.284-287, there is significant warming in the S. Hemisphere oceans which will do no good to the ice shelves in Antarctica.

    This line of thought led me to revisit Mercer, Nature, 1978, v271 pp.321-325. I reproduce a sentence here:
    “One warning sign that a dangerous warming is beginning in Antarctica, will be a breakup of ice shelves in the Antarctic Peninsula just south of the recent January 0C isotherm; the ice shelf in the Prince Gustav Channel on the east side of the peninsula, and the Wordie Ics Shelf; the ice shelf in George VI Sound, and the ice shelf in Wilkins Sound on the west side {Fig 2).”

    I note that each of these shelves is in retreat or gone, as shown by the following:
    http://www.iitap.iastate.edu/gcp/sealevel/ross.html
    Smith et al. Antarctic Science, 19(1), pp131-142 (2007)
    http://pubs.usgs.gov/fs/fs17-02/fs017-02.html

    I should really go back and reread Weertman, Hughes, and some of the other ‘instabilists’ …

    sidd

  30. 30
    ray ladbury says:

    OK, Vernon, I’ll bite. How does black carbon on the ice caps warm the entire Northern Hemisphere. And while you’re at it, maybe you can explain where the “sulfates” that block the IR come from and how they succeed in keeping the IR away from the CO2. Maybe you could tell us where the IR comes from.
    Vernon, this brings up a question. With so little knowledge of the theory behind anthropogenic climate change, how do you even know what you are opposing? You seem to think there is some region where the CO2 resides, and if you can just keep the IR radiation away from it, you won’t get any warming. Please, Vernon, I am sincere when a beg of you to do some reading on this site. Ask some question about the theory and why scientists who study this subject are convinced that 1)the climate is changing, and 2) we are behind those changes. I strongly recommend the essays “A Saturated Gassy Argument” and “What Angstrom didn’t know” a couple of essays down. Vernon, you owe it to yourself to be well informed that you can at least state the argument of your opponent correctly. I don’t care if you stay a skeptic, but at least learn what you are skeptical of.

  31. 31
    Ian Forrester says:

    Re #18: Vernon said: “If the Arctic warms and releases all trapped greenhouse gas, then why when the Arctic melted last and Greenland mostly or completely melted did the CO2 level not go up”?

    The CO2 did go up but only by a small amount. The large increase in CO2 concentrations since the 1850′s is due to the release of “fossil carbon” buried and unavailable for release into the atmosphere until we started mining, pumping and burning it.

    Ian Forrester

  32. 32
    Sam says:

    Re: 26
    Tim – I cant find the cite just now. I agree that Gavin’s explanation is consistent with AR4 and the finding of the new paper. The press release was misleading, and I owe Gavin an apology for my initial reaction to his reply.

  33. 33
    Vernon says:

    RE: 30 Well, I believe Gavin knows about this and it is what he said in #5, that sulfates cool by reflecting energy before it is absorbed. The UC Irvine study says that Arctic warming and melting (between 35 to 94 percent) is caused by dirty snow. Black carbon could then be responsible for almost all observed warming and melting in the Arctic. This indicates we need further studies since it is possible that almost all warming in the Arctic is due to black carbon.

    The significant question is how much warming is due to carbon black and now much to other factors. There are three possible outcomes:

    Black Carbon is low end (35 percent) and CO2 theory still works.

    Black Carbon is middle range (~65 percent) and CO2 sort of works but is not as much a driver as predicted.

    Black Carbon is high end (94 percent)and CO2 is not a driver for global warming.
    -Basically, the dirty snow is melting the ice cap which caused more heat to be absorbed and releases the trapped methane. This warms the water cause a slight NH warming.

    So this becomes something we can test now and would want to know to help the GCM accuracy.

    [Response: Possibility 4. There are multiple impacts on Arctic temperature both warming and cooling that can’t be distinguished in a single factor study with no other constraints. You appear to want to believe that this is a zero sum game – if factor X is bigger than was thought before, factor Y must be proportionately smaller. This is simply a fallacy since there are factors A, B, C and D which all have uncertainies and since only the sum total of the factors is constrained you can’t conclude that the error is in Y. Hard as it might be to believe, the sensitivity to 2xCO2 in the Arctic or elsewhere, is independent of the effects of black carbon, ozone, methane or sulphates. – gavin]

  34. 34
    Vernon says:

    Gavin I agree, I am just pointing out that it is not just CO2 as some seem to stress. That there are many aspects and based on the UCI study, we need more information to determine the relationship between various aspects.

  35. 35
    sidd says:

    Re: Comment by Vernon � 9 Jul 2007,5:15 pm

    Hansen and Nazarenko
    http://www.pnas.org/cgi/reprint/2237157100v1.pdf
    have a discussion of the forcing due to soot through change in albedo.
    The first sentence of the Summary:
    “The soot effect on snow albedo may be responsible for a quarter of global warming.”

    Now that I am on the subject of Hansen: In Phil. Trans. Royal Soc. A (2007), v365, pp. 1925-1954, Hansen et al. argue for an ice sheet albedo flip mechanism to explain abrupt glacial terminations. They point out that the timescales seen in paleo records reflect the timescales of the NH spring insolation forcing and not the fastest timescales possible for icesheet disintegration; i.e. these paleo timescales are upper bounds, rather than lower bounds for icesheet decay. A case is made that the appropriate climate sensitivity including albedo flip effects is 1.5C/(W/m^2) rather than 0.75C/(W/m^2). (There is also some discussion of black carbon effects). In sum, the possibility that substantial melting can occur on timescales as short as a century cannot be ruled out.

    I really shouldn’t look at Mercer and Hansen in the same afternoon…

    sidd

  36. 36
    ray ladbury says:

    Vernon said, “…we need more information to determine the relationship between various aspects.”

    We always need more information. The question is whether the information will change the conclusion that we have to address this threat. CO2 forcing is the part of the equation we know best. It is constrained by several independent lines of evidence. In the extremely unlikely event that we were to find a forcing that we had not anticipated, it would not affect CO2 forcing, but more likely one of the forcings where uncertainty is greater (e.g. aerosols). So pumping more CO2 into the air would still result in significant warming.
    Now let me explain why it is a very bad idea to wait to act. CO2 is increasing exponentially in the atmosphere, and we know that the climate has positive feedbacks as well as negative. That is not a recipe for stability. What is more, we don’t know when these positive feedbacks kick in with a vengeance. We know it hasn’t happened yet, so maybe if we are lucky we can take some common sense actions, we can slow the warming enough to buy time so we can develop technologies and strategies mitigate the threats and take advantages of any benefits in a warmer world. The advantage of acting now is that we have a bit longer before the positive feedbacks kick in, AND people aren’t panicked. The latter is particularly important because people do foolish things when panicked–like wrecking the economy, electing authoritarian rulers, etc. Time is an awfully precious commodity when you’re talking about a system with positive feedbacks.

  37. 37
    James says:

    I am rather puzzled by some of this. If I understand correctly, the argument is that DNA was found preserved in ice that’s much older than a time when it was assumed that the Greenland ice cap had melted completely, no? From which some people seem to conclude that the known sea level rise couldn’t have come from melted Greenland ice cap.

    But IIRC, the cap today is something like 2 km thick, on average. It seems obvious to me that if say 90% of that had melted, that’d leave a 200 meter thick layer ice cap, and still been within error limits for sea level rise. Where am I going wrong?

  38. 38
    David B. Benson says:

    Re #36: James — You could be right, but most assume that about half of the sea level rise resulting from melting of some of the West Antarctic ice sheet.

  39. 39
    llewelly says:

    I was under the impression that ice core sites were typically chosen to minimize the extent to which the ice had moved in the past, in order to minimize folding and jumbling of ice layers. It seems to me that sites with relatively little ice movement would also be highly stable in terms of presence and thickness of ice. Doesn’t this result in a strong bias toward sites more likely to have ice (at any given time) than randomly selected sites of similar latitude and altitude? How did the researchers account for this?

  40. 40
    biffvernon says:

    Re #27. In his account of the Voyage of the Beagle, Darwin described his encounter with un-clothed folk of Tierra del Fuego who met the Beagle in their canoes: “..a woman, who was suckling a recently-born child, came one day alongside the vessel, and remained there out of mere curiosity, whilst the sleet fell and thawed on her naked bosom, and on the skin of her naked baby!”

    Inferring temperature form clothing assumes others are as soft as us :)

  41. 41
    Chris S says:

    Read this last night. Even CNN who tries at least to report the effects of global warming and climate change indicators, often times like to make controversy. The article on CNN.com first mentions that half a million years ago, greenland was “green” and that the climate was “different” then, in one sentence at the bottom (when most readers will loose interest) mentions what RC did about the dating potentially being only 116k years old. It’s so annoying.

    Here’s the link. Thought I’d stop by and drop it off here. Sorry if its been posted : I find it funny that theres an article on CNN about this a day after RealClimate.org posts a blog about it.

    http://www.cnn.com/2007/TECH/science/07/06/oldest.dna.ap/index.html

  42. 42
    Andrew Sipocz says:

    Wikipedia comes to the rescue again.

    http://en.wikipedia.org/wiki/Greenland_Ice_Sheet_Project

    A quick discussion about the reasoning behind the locations of various ice cores on the Greenland Ice Sheet.

  43. 43
    Vernon says:

    RE: 36 Ray, if the Arctic warming is possibly due to black carbon, what studies have been performed to support Gavin’s argument, that sulfates are causing cooling which is masking CO2 based warming? If there are no sulfates doing the cooling, and the dirty snow is doing the warming (for this argument, taking the high figure) then where is the signal for CO2 based warming? In fact, this leads to the question – is dirty snow warming the Arctic and the warming Arctic causing NH warming? This argument is within the bounds of the UCI studies results.

    [Response: You keep repeating the same statement, and you will keep getting the same answer. The whole premise of your BC vs. CO2 question is simply false. – gavin]

  44. 44
    Vernon says:

    Gavin, why is it false? There is a known empirical source of Arctic warming (BC – which needs to be further studied) and a unknown amount of cooling (sulfates – which I cannot find a study of for the Arctic) and a theory of CO2 based warming. If the study for the sulfates exists, then there would be empirical proof of cooling. These would either support or not support the Theory of CO2 based warming. I am asking where the study is for sulfates?

    [Response: If you want to see what all the different effects of all the different forcings are, try reading Hansen et al 2005 or 2007. There you have 14 different forcings (including sulphates and BC and CO2), conveniently grouped into only 8 experiments, and where you can see the different effects on the Arctic and the globe. Only the sum total of the effects is constrained (since the Earth has only run one experiment for us), and the true attribution to any one element has to be assessed using models that include all of the effects. The truth is that this is complex and jumping to conclusions based on simplistic readings of press releases just isn’t going to lead you to enlightenment. – gavin]

  45. 45
    Jim Eager says:

    Re 34 Vernon: “Gavin I agree, I am just pointing out that it is not just CO2 as some seem to stress.”

    But why do you then assume for argument that carbon black accounts for 95% of Arctic melting and warming and ignore all other factors?

  46. 46
    Vernon says:

    RE:45 well, it could be because a UC Irvine study indicates that it is. See #5. That is why I am looking for a study of sulfates to support Gavin’s argument that the CO2 forcing is hidden by the sulfate cooling. I may have miss read the Hansen 2005, but I though it said that “The aerosol scenario in our model uses estimated anthropogenic emissions from fuel use statistics and includes temporal changes in fossil-fuel use technologies” and I did not see any listed sulfate studies for the Arctic. Are we now assuming that sulfates are going to be homogeneous? If so, where is the studies that supports that position?

    Models are nice but where are the empirical studies that support this in light of UCI’s study of Arctic warming? That is why I keep asking the same question.

    [Response: But the Irvine study is a model…. and if you can’t find the Hansen discussion on the role of aerosols, go here and generate the plots for yourself: http://data.giss.nasa.gov/modelE/transient/Rc_ij.1.08.html – gavin]

  47. 47
    Hank Roberts says:

    Vernon, you’re using the word “theory” as though it meant “speculation” aren’t you? You have the notion that if you can explain everything with one factor, the others can be assumed inconsequential?

    Consider: your childhood allowance on an annual basis may have been about equal to your parents’ annual tax refund from the IRS. That doesn’t mean you can zero out any other possible forcings and feedbacks to understand the family budget.

  48. 48
    James says:

    Re #38: [Re #36: James --- You could be right, but most assume that about half of the sea level rise resulting from melting of some of the West Antarctic ice sheet.]

    Yes, I understand that, but it wasn’t really my question. It appears that the reasoning uses a binary “melted/not melted” function for the Greenland ice cap, while to me it seems that the “not melted” state has a lot of room for changes in thickness, and hence volume of water in the oceans, while most of the land area of Greenland is still ice-covered.

    The difference, I think, is that Greenland’s ice would mostly just melt, while the West Antarctic ice is held back by gounded ice shelves, so that a small rise in sea level might trigger large increases in glacial flow. No doubt that’s over-simplified, but is it fundamentally wrong?

  49. 49
    Lynn Vincentnathan says:

    When I read the media reports, my thinking was, with a BAU scenario (to which we seem committed), it’s probably going to get a lot hotter than 125,000 yrs ago, so the fact that there was ice in that era means all the more ice to be melted in our anthropocene era. It doesn’t look good. We could be headed toward a 55 mya scenario, not a 125,000 yrs ago scenario. And then all the black soot melting it faster. We’re in very bad shape, I’d say.

    ***********************

    Another media report on the Western U.S. drought/fire conditions last night. The U of AZ scientist more or less indicated it was due to warming (and concomitant dryness/evaporation & wind patterns — sounded a bit tautological to me), but when the reporter pressed her if it was due to our AGW & GHGs, she focused solely on the notion that there had been such natural drought fluctuations in the past and it could be a natural (not human induced phenom) now. Well, I’d like to add that it COULD BE due to AGW, as well. And what kind of evidence is there that we are due for a “natural” drought spell — she didn’t give one iota of evidence for that, while we do have a lot of evidence that GW is happening.

    Why is “natural” the default, and “human-caused” admitted only if we are 95% or 99% sure? How about “human-caused” as the default in this anthropocene era (since at least we can do something about the problem, and we would thereby feel more empowered), and “natural” only the back-up alternative possibility?

    Then if we’ve done all we could to reduce our GHG (thereby strengthening our economy and bank accounts in the process), and we find out later lo & behold it was only “natural,” no harm done & we can use our savings to help us adapt to the “natural” problem.

  50. 50
    Philippe Chantreau says:

    Lynn, empowered, also means responsible, that’s why people are so reluctant to admit AGW, among other things. It was so much nicer, in the old days, when God was responsible for plague epidemics, gangrene, volcanic eruptions, hurricanes and even grandma’s lethal CHF exacerbation. Then, it was out of our hands, and, as terrible as it sounds, that carries some freedom. Now, we know better, but we don’t really want to be responsible, we still want the freedom.


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