Arctic Sea Ice decline in the 21st Century

Figure 4: Northern Hemisphere sea ice extent in September from model integrations submitted to the IPCC AR4 with observations from satellite era shown in black.

4) Is it too late to save the sea ice?

The future emissions scenario discussed here is one that assumes modest increases in emissions. If humans can reduce the rise in emissions compared to this, then sea ice retreat would be slower and rapid events would be rarer, according to the IPCC AR4 models.

5) Have we crossed a tipping point?

I don’t think we have yet. If we fix the greenhouse gas and aerosol levels at year 2000 values and run the model into the 21st century, the sea ice retreats for only another decade or two and then levels off (some of the ensemble members even recover a little bit). So according to our model, the sea ice does not appear to have passed a threshold yet. We have not done an exhaustive study of any years beyond today, so unfortunately we cannot say with certainty that no tipping points exist. The bottom-line: The retreat can be surprisingly rapid even without clear evidence of a tipping point.

I thank Dr. Holland for valuable suggestions to improve this post and providing Fig 1. I thank Ian Eisenman for computing ice extent from the IPCC AR4 models shown in Fig 4. I look forward to reading your comments and questions.

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127 comments on this post.
  1. Todd Albert:

    Great post. I look forward to reading the article, but I always love these clear explanatory summaries.

    The last two questions (too late, tipping point) are the types of questions I am asked most often by students, community members, peers, and others. I appreciate your hopeful answer and it lends credence to my typical answers.

  2. cat black:

    re #1 [tipping] Seems to me that the most balanced answer would be that tipping points in Arctic ice melting may exist simply because they cannot be fully ruled out, and further more if they do exist then they may fall anywhere on the continuum of future data points, including the second Wednesday of any future (or even recently past) month you’d like to choose. One guess being more or less as good as another, given the current state of our knowledge.

    Not very satisfying, I suppose, for people who want “the answer”. But then again, allowing them to choose any second Wednesday for the point beyond which things are FUBAR might get across the larger issue, which is that they are, in some real way, making that choice every day in how they live their lives, and measures they are, or are not, taking to stave off this interesting little disaster looming on some random second Wednesday, in some random month, in some random year.

  3. Hank Roberts:

    Dr. Bitz, have you heard from any researchers in other fields whose subjects have had the Arctic ice as a background assumption, who are now looking for what happens in their area of interest as this change happens?

  4. Andy Revkin:

    Great followup, and much appreciated (from one who wrote about the paper here:
    Best journalism results from ongoing ‘conversations’ with scientists, which is facilitated by this kind of presentation. Worst journalism happens when everyone only focuses on an issue of this sort in the short span of hourse between when the press release is issued and the deadline looms.

  5. Phillip Shaw:

    Just a note to say that the link to bitz_fig4.jpg may be broken. It just take me back to the home page.

    [Response: fixed. Thanks - gavin]

    On a more positive note, this site is a ‘must read’ for anyone interested in learning more about climate change. Your hard work makes it very readable to the typical layperson such as myself.

  6. Charles Muller:

    Thanks for this interesting post.
    Do we know if Artic was free-ice in past climates ? I read that some peri-artic zones like North Siberia were probably warmer than present at some periods of the Holocene Climatic Optimum (8000-6000 BP), and that summer orbital forcing 60°N and poleward was much more important during the last interglacial (Eemian). Is there any proxy (or model reconstructions) for Arctic ice conditions during these times?

  7. Brian:

    Can you someone point me to some quality reports regarding how life w/could be affected by zero sea ice?

  8. Alastair McDonald:

    Dear Dr Bitz,

    Can I first thank you for putting your head above the parapet.

    The idea of a tipping point for the Arctic sea ice was first described in a now unfairly neglected book “Climate through the Ages” by C.E.P. Brooks, who was a leading British meteorologist sixty years ago. The point is that because the ice albedo effect is a positive feedback, in a warming world it will inevitably lead to a sudden collapse of the ice.

    As the Arctic ice sheet contracts the ice albedo decreases causing the melting to accelerate. It is this acceleration which ensures the rapid collapse of the ice sheet.

  9. John L. McCormick:

    RE # 3

    Hank, I get the gist of your question.

    I want to see the National Academy of Science devote time and attention to the Western North American precipitation and temperature changes as the Arctic Ocean 90 percent albedo shifts to 40 percent absorbent.

    Certainly that dynamic deserves as much attention as was applied to the arbrupt climate change study. In fact, an ice-free Arctic by 2050 IS ABRUPT CLIMATE CHANGE.

    The convective currents from the Gulf and Southwest would IMHO be affected and likely cause planting and harvesting impacts in the world’s grain basket.

    Are we building a corn-to-ethanol industry in a box canyon?

  10. Richard Jones:

    I enjoyed reading the essay, but isn’t A1B the most pessimistic of the IPCC scenarios, with CO2 increases > 1% pa (i.e. doubling the rate of historic growth)?

    What happens in mid-low case scarios?

  11. pete best:

    Dear RC

    I bet it was the left wing media that reported the worse case year 2040 scenarios.

    Great work, once again we are shown that tipping points have not been demonstrated in the models are the alarmist 2040′ers are going a little over the top. It also gives us hope that by reducing emissions to year 2000 levels would be a good start and seems likely to happen if we weren’t for that fact that we are going to experience a third world population explosion by 2050.

  12. Alastair McDonald:

    Dear Peter,

    Even if we reduce CO2 levels to those before the year 2000, say the year 1997, the ice will continue to melt at the rate it was melting then – 10cm per year, see

    “… the SCICEX data indicate that ice has continued to thin in some regions throughout the 1990s, at a rate of about 0.1 meter per year..”

    In 1997 it was 2m thick. If it has continued to melt at that rate, then it will be gone by 2017, not 2040. If the thinning has accelerated, and/or there is a minimum thickness for sea ice of say 0.5m, then it could disappear much sooner. With the effect of an El Nino it could go this summer!

  13. Eric Swanson:

    Dr. Bitz,

    I was concerned about the strength of the sea-ice/ocean albedo feedback for many years. In 1992, I presented a paper on the subject and have tried to follow the science ever since.

    After reading your paper last month, I corresponded with Dr. Holland and also looked back at some of the work which was published after the SHEBA experiment. Also, I read some of the CCSM 3.0 manuals, seeking more information.

    After a brief look, I found that there appears to be no zenith angle dependence in the albedo for the ocean, but that a fixed value of 0.06 is used. I showed back in 1992 that this is value was incorrect for the direct beam component of the incident solar energy. This was found by Payne in 1972 (J. Atmos. Sci. 29, 959), who published results of a tower experiment over the open ocean. It is also quite likely that the albedo of sea-ice, especially when it is covered by melt ponds, could be a function of zenith angle. From what I’ve been able to learn of the SHEBA project, there was no measurement of the direct component of the insolation, only the hemispherical radiance on a horizontal surface. Lacking measurements of the direct component, it would appear to be difficult to quantify the effect of zenith angle on albedo.

    As an engineer who has studied solar energy systems, I know that the difference between the direct insolation and the diffuse energy can be very important. Dr. Holland agreed that the model could be improved if zenith angle effects were included. I wonder what you think about this question and why there has been so much trumpeting of your results, given the need for this obvious improvement in your models.

    Best Regards,

  14. Charles Muller:

    A point I don’t understand in your GRL paper :
    “The model is run at a nominally 1-degree resolution with the north pole displaced into Greenland.”
    What is exactly meant by this “displacement” of North Pole to Greenland ?

  15. Pascal:

    thanks for this article

    in fig1, I see a relative stability of sea-ice extent between 2005 and 2025 (about).
    How can you explain such a phenomenon?
    Is this the beginning of perennial ice (thicker) melting?

  16. Edward Greisch:

    Thanks for actually showing multiple runs on the graphs.

  17. Jeff Weffer:

    Won’t the ice just freeze back in the Winter?

    When the arctic circle goes into six months of darkness from September 21 to March 21 for example?

    The sea ice has already frozen back and now covers all of the Arctic. It won’t start melting again until July.

  18. crandles:

    In its annual review of 2006,

    NCDC says:
    “Arctic sea ice conditions are inherently variable from year to year in response to wind, temperature and oceanic forcings. Quite often, a “low” ice year is followed by recovery the next year. But increasing surface temperatures in high latitudes have contributed to progressively more summer melt and less ice growth in the fall and winter. While natural variability is responsible for year-to-year variations in sea ice extent, three extreme minimum extent years along with evidence of thinning of the ice pack suggest that the sea ice system is experiencing changes which may not be solely related to natural variability.”

    Is it reasonable to ask how frequently in your simulations you see situations where there is such a sharp acceleration which lasts for at least three years like we have seen in the last three years? In what proportion of such similar situations in your simulations does the faster rate continue for some time?

    I created this:

    4.5 times faster may make it look like your extreme case of 4 times faster look quite conservative but it is important to realise you are looking at longer periods than three years. I could be jumping in and worrying too soon but it appears I am not the only one seeing a change in behaviour of the ice extent.

  19. Paul M:

    Scientists like the ones on here have a peculiar job to do. They are born on the planet, nurtured by parents or adults who care obviously cared , and retain enough of their youthful curiosity to become members of the scientific community. Now they have to examine the ultimate demise of the very conditions that nurtured and supported life systems. Just like in the high school titration lab experiment, there will come a point (sooner than later) when BOOM, everything changes. Spring 2007 will be a time which will be studied millenia from now, if there are survivors to study it. Metaphorically speaking, we are all examinig why the tide is out like it is, not realising the tsunami that is on its way. I hate to be the gloom and doom guy, but get up, open your door, and look outside.

  20. Cecilia Bitz:

    Thanks for everyones’ comments.

    Post 7 and 18, I’ll get back to you when I am in my office ASAP.

    Post 3 Have I heard from researchers with interest in the ice retreat? I am in contact with several biologists in my universtity and others that I have met in various meetings.

    Post 10 Isn’t A1B the most pessimistic SRES scenario? There is a good figure showing CO2 concentration levels in the A1B, A2, and B1 scenarios along with the full range of concentrations in all SRESscenarios at (scroll to bottom) Only the A1B, A2, and B1 SRES scenarios were completed by most modeling centers for intercomparison
    in the IPCC AR4. Of these three, A1B is in the middle, but the three only really diverge after 2050. So there is not much point in arguing about their relative levels prior to 2050. Furthermore, CO2 is not the only relevant greenhouse gas. The rapid events we found are more common in runs with higher GHG levels. There is a better chance of avoiding rapid events if we can reduce our GHG emissions.

    Post 13 Obvious need for improvement in models? Actually, the ocean surface albedo is not fixed at 0.06 in the model. It is a function of zenith angle and diffuse/direct beam. The details are in the CCSM3 coupler manual section 16.3.3 Ocean Surface Albedos

    The albedo is 0.06 only if there is no diurnal cycle in the model, which we sometimes use in test mode. However all the runs presented here and completed for IPCC AR4 have a diurnal cycle. The zenith angle dependence compared favorably to SHEBA data from Scott Pegau.

    Post 17, Doesn’t the ice freeze back in Winter? Yes it does, see my parenthetic note “(The sea ice grows back at least for some portion of winter for the duration of the 21st century.)” in paragraph 5. The link between sea ice and climate varies with season. The retreat is mainly in summer. The ice grows back in winter but remains thinner all year. In fact, Rothrock et al 1999 found the ice is 40% thinner in the central Arctic in the 1990s compared to submarine tracks taken prior to 1976. These submarine tracks were taken in later winter! The thinner ice then retreats faster in summer according to observations
    and models.

  21. Michael Salem:

    Has commenter #11 misread the article? This person seems to think that ice stops retreating when emissions are reduced to yr 2000 levels, but I read the article to say that ice retreat stops when emissions are cut to zero and atmospheric greenhouse gas levels are reduced to yr 2000 levels. Which interpretation is correct?

    [Response: The latter (well, roughly). As long as emissions are non-zero, the rate of increase in greenhouse gas concentrations is positive, i.e. greenhouse gas concentrations continue to increase, and the enhanced (i.e., anthropogenic) greenhouse effect strengthens, temperatures further warm, and ice further melts. Decreasing the rate of emissions does not stabilize the greenhouse gas concentrations, it simply decreases the rate of their increase. -mike]

  22. Hank Roberts:

    This is another paper mentioned here a while back; I’m curious whether the Navy data sets have any more information than is publicly available and whether their conclusion is much different.

    “… an analysis of the diminishing sea ice trend in the Arctic Ocean by examining the NPS 1/12-degree pan-Arctic coupled ice-ocean model. While many previous studies have analyzed changes in ice extent and concentration, this research focuses on ice thickness as it gives a better indication of ice volume variability. The skill of the model is examined by comparing its output to sea ice thickness data gathered during the last two decades. … The NPS model indicates an accelerated thinning trend in Arctic sea ice during the last decade. The validation of model output with submarine, EM and ICESat data supports this result. This lends credence to the postulation that the Arctic not only might, but is likely to be ice-free during the summer in the near future.”

    Also thanks for the response about interest from other researchers — I’m very curious what the biologists make of this change, in particular because I gather we’re still assuming that the biological recycling of carbon is going to stay effectively the same over the short term (as implied in Mike’s response above). I’ve wondered if the biologists will see any paths that include a significant fast change in biology, likely plankton species or abundance, that might alter how well the biosphere handles CO2 on an annual basis.

  23. Julie Brigham-Grette:

    Post 6. Yes there is evidence for less sea ice during the Eemian. Some of us argue whether the entire Arctic was ice free in summers, so the answer is still out on that. But see this review and references there in for documentation on sea ice, marine temperatures, tree line movement etc.
    CAPE Last Interglacial Project Members, 2006, Last Interglacial Arctic Warmth Confirms Polar Amplification of Climate Change, Quaternary Science Reviews 25, 1383�1400

  24. Judith Curry:

    Hi Cecilia,

    Very interesting paper and post. I would appreciate your assessment on the possible impact of missing or perhaps overly simplified physics from sea ice models that are used in climate models in your projection. I fully appreciate that the sea ice model that you are using is among the most sophisticated sea ice models currently being used in climate models. However, based upon my understanding of your sea ice model (and other sea ice models used in climate models), there are several processes that are highly simplified that would be expected to, with a less highly parameterized treatment, influence the ice albedo feedback (note some of these processes are mentioned in chapter 7 of IPCC TAR):

    - explicit melt ponds: albedo, latent heat, salinity effects
    - ice age effects on optics and thermodynamics, particularly for first year/thin ice and frazil ice
    - lead width distribution: impact on lateral melting and wintertime turbulent heat fluxes
    - treatment of fast ice
    - snow: nonlinear conduction, metamorphism, redistribution
    - ridged ice: including enhanced bottom melting

    While I understand that this blog is not the forum for detailed scientific explanations, I would appreciate a summary sense from you as to whether the incomplete treatments I’ve listed might collectively be likely to accelerate the melting or act to stabilize the ice. Do you see any possibilities among the list above that might provide a negative feedback that would help stabilize the ice? My basic concern is that the sea ice models that perform best in the current climate may have inadequate treatments of a warmer climate that is dominated by first year ice, very thick ridged ice and seasonal fast ice, and may have inadequate treatments of surface albedo and thermodynamic processes that would alter the transition from the current sea ice regime to the modified regime as a result of the projected warming. My own sense is that the loss of much multi-year ice could occur more rapidly than the models project, but the transition to a completely ice free arctic during summer would be slower than projected. Thanks for any insights that you can provide on this.


  25. Alexander Ac:

    Re #22
    Considering the response of organisms to changes in the weather and climate is very complicated and in fact not a serious biologist would be able to predict the implications of certain future change. E.g. food chain and interaction between organisms are so complicated, that we can only “expect” some changes, but we to not know them for sure. What is more sure, that “in general” WE CAN say, that the more rapid change, the worse for organisms with low ecological valence and the better for organisms with high ecological valence (e.g. opportunistic organisms…). And of course from the past we know, what a rapid changes always brought – death to many, but life to others…
    As an starting ecophysiologist, I have a feeling, that the global primary productivity of terrestrial ecosystems (and hence the CO2 absorbing capacity) ecosystems will decrease with increasing rate of climate change and in fact, it already seems to be decreasing. For instance, during the El Nino years (especially 1998), there was a greatest interanual increase in the CO2 concetrations, mainly due to high “global stress” caused by adverse effects of El Nino… this year we should observe similar pattern.

  26. Steve Reynolds:

    Re 21:
    Mike’s response> As long as emissions are non-zero, the rate of increase in greenhouse gas concentrations is positive…

    It is my understanding that both ocean and land are currently absorbing a large fraction of CO2 emissions, so at a rate that must be faster than the pre-industrial rate. Then emissions should not need to go to zero for CO2 concentration to decrease. Am I missing something?

    [Response: You misunderstand how these processes work. We are perturbing the carbon cycle from a pre-anthropogenic equilibrium. Carbon uptake by the ocean and terrestrial biosphere can only take up some finite positive fraction of the carbon produced by anthropogenic sources. The uptake processes simply act to slow the accumulation of greenhouse gases in the atmosphere relative to the rate at which it is being created by fossil fuel burning. There is no plausible mechanism that would allow natural uptake to produce a decrease in actual greenhouse gas concentrations in the face of positive anthropogenic emissions. As long as anthropogenic emissions are positive, greenhouse gas concentrations will increase. Interested readers are referred to the discussion in IPCC(2001). -mike]

    [Response: Actually, come to think of it, its a bit more complicated than that. It depends on the residence timescales of the various reservoirs. At sufficently low future emission rates we could eventually stabilize at concentrations lower than the current concentration, but not before reaching intermediate concentration levels higher than current. A nice comparison of CO2 emissions scenarios and associated future CO2 concentrations histories is available here. I'll leave it to the carbon cycle specialists to comment further...I now see that David has already discussed this previously better than I can. I would refer folks there. -mike]

  27. Alan:

    Re #11: “I bet it was the left wing media that reported the worse case year 2040 scenarios….if we weren’t for that fact that we are going to experience a third world population explosion by 2050″hasis)

    Hi Pete, a couple of questions. What “wing” of the media did you get your fact from? In the light of Cecilia’s lucid explaination, is it more politically correct to be an “alarmist”, an “ostrich” or a “deer in the headlights”?

    Thanks Cecilia for explaining the caveats to the “2040″ headline, if more scientists made this kind of effort the internet would soon make bad science journalisim redundant.

    Perhaps the public’s preocupation with “tipping points” is the same phenomena seen when a mechanic advises that “you need new brake pads soon”, the first question many people ask is “how soon?”. To carry the anology a bit further, most will maintain their brakes as advised, some will wait until the pads are gone and the discs need machining, a minority will crash into a tree rendering the question moot.

  28. Edward Greisch:

    I like the article and the downloaded paper. Could somebody please write a paper on when the famine will start in the USA? To most people, global warming is good. They don’t like winter and they are afraid of polar bears. [I'm afraid of bears too, but I like winter because there is no pollen in winter.] Most people would see the opening of the Northwest Passage as an economic benefit. As for the famine, most people would “let the grandchildren handle their own problems”. Most people also say: “We will adapt”, not knowing that adaptation is 99.999% death and extinction.
    Thanks for the opportunity to download papers from Dr. Bitz’s web site. Again, and knowing that you really can’t say and the problem is too hard, please write a paper on when the famine will start in the USA. AGW won’t be seen as bad until it is seen as bad for Human Americans.

  29. yves fouquart:

    Hi cecilia and congratulations for this nice post that I found quite clear.
    Regarding to Judy’post, my question concerns the dynamics of high latitudes. Did you find any evidence for a significant change in dynamics and cloudiness in summertime in the Arctic regions in these simulations?

  30. Charles Muller:

    #23 Thank you very much for the review, Julie. According to fig. 4, summer insolation forcing (compared to present) could have reached 40-75 W/m2 during the thermal maximum of the LIG – much more that any projection of GHGs forcing on 2050 or 2100 for the same melting season (JJA), I guess. But I suppose we must take account of winter negative anomaly for the same orbital forcing.

  31. Anonymous:

    Dr. Bitz,

    Building on question #29, the link you referred to about cloud cover is a discussion about the paper put out by Francis & Hunter. I am confused about the use of Maximum Ice Retreat Anomalies (MIA) and the evidence that supports a negative correlation between MIA and DSF. A negative correlation? Does anyone know what this means for the ice-albedo feedback? Is DLF a prominent player in any of your ensembles?

  32. george naytowhowcon:

    I have been monitoring Arctic Sea Ice minima / maxima extents for the last two years. I suggest that aerosols used for cloud forcing are creating a positive feedback of arctic surface temperatures during summer melts. The forced cloud cover acts as an insulating blanket trapping the earth’s radiant heat rather than allowing for cloudless nights to cool surface temps. Radiational cooling happens when there is little or no cloud cover.Thus increased summer melt. The remarkable recovery of the arctic sea ice is plainly visible. Currently, the Arctic Sea Ice is reaching out into the pacific from the berring streight, somewhat annomolous and demonstrates that it is indeed very cold there. The curiousity of the tropical jet of the eastern pacific crossing N. America and the Atlantic Ocean providing a warm winter to Moscow and Europe in general seems to have pushed Arctic air to South Asia. Are there any climate models showing the establishment of new path’s for mid lattitude jet streams consistent with Global Warming climate models?

  33. Charles Muller:

    On the same subject (and also same journal and same publication month), I mention thereafter M. Winton’s analysis of some IPPC FAR models dealing with “tipping point” for summer Arctic sea-ice conditions.

    GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L23504, doi:10.1029/2006GL028017, 2006

    Does the Arctic sea ice have a tipping point?

    Michael Winton
    Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, New Jersey, USA

    Abstract – Two IPCC fourth assessment report climate models have Arctic Ocean simulations that become sea-ice-free year around in 1%/year CO2 increase to quadrupling experiments. These runs are examined for evidence of accelerated climate change associated with the removal of sea ice, particularly due to increasing surface albedo feedback. Both models become seasonally ice-free at an annual mean polar temperature of ~9°C without registering much impact on the surface albedo feedback or disturbing the linear relationship between Arctic Ocean climate change and that of the surrounding region. When the polar temperature rises above ~5°C, however, there is a sharp increase in the surface albedo feedback of one of the models, driving an abrupt elimination of Arctic ice and an increase in temperature above that expected from warming of the surrounding region. The transition to ice-free conditions is more linear in the other model, with ocean heat flux playing the primary driving role.

  34. William Astley:

    In reply to comment 28 “…Could somebody please write a paper on when the famine will start in the USA? To most people, global warming is good. … As for the famine, most people would “let the grandchildren handle their own problems”. Most people also say: “We will adapt”, not knowing that adaptation is 99.999% death and extinction…”

    The above article does not state that warming of the arctic, is a catastrophic climate event.

    There is a general misconception concerning the relative affects and danger of planetary cooling as opposed to warming.

    Famine has occurred in the past, due to cooling of the planet, not warming. The planet is at the end of the interglacial period and has started to cool. The warmest planetary temperature in this interglacial period occurred roughly 8500 years ago. At that time the tree line, in the arctic, was roughly 200 miles north of its current location. (Lamb has a picture of the arctic tree stumps in his book “Climate, Past, Present, and Future, and notes that the stumps, indicate that the tree line in the arctic was roughly 200 miles north of its current location.) The planet was roughly 2C warmer, 8500 years ago, as compared to current temperatures.

    As the planet is 70% covered with water, when it is warmer there is more rain. For example, during the Holocene climatic optimum (warmest period during this interglacial), the region that is now the Sahara desert was a savana, that supported Elephants, Rhinos, and so forth.

    The planetary climate is unstable and drier during the colder glacial period. For example, there was an 800 times increase in dust in the Greenland ice sheet proxy data during the glacial period as compared to current conditions. There was an order of magnitude increase in sea salt in the ice sheet data, which indicates a massive increase in storms, during the colder glacial period as compared to the current warmer interglacial period.

    Life is difficult during the colder glacial period. For example, the early human population was reduced to less than 20,000 as a result of the climatic affects of the Toba eruption, which occurred roughly 70,000 years ago, during the glacial period.

  35. Ike Solem:

    Thanks for the informative post. The 1999 paper, “Thinning of the Arctic Sea Ice Cover” can be found at

    “In summary, ice draft in the 1990s is over a meter thinner
    than two to four decades earlier. The mean draft has
    decreased from over 3 m to under 2 m, and volume is down
    by some 40%. The thinning is remarkable in that it has
    occurred in a major portion of the perennially ice-covered
    Arctic Ocean. This is not a case of thicker ice appearing
    in one region simultaneously with thinner ice appearing in
    another, induced perhaps by a change in surface winds and
    ice advection.”

    The combination of decreasing thickness and extent, as well as less recovery of winter ice in each successive season, indicates that the trend is not an anomaly. There is more data on decreased winter ice recovery.

    Keep in mind that at the same time there is an ongoing trend of melting Arctic permafrost. Since ~30% of the global soil carbon is locked up in the permafrost, it is possible that this could impact the global carbon cycle. There is also the issue of methane clathrates (RC)

    For more on the permafrost issue, see:
    â��Boreholes in Svalbard, Norway, for example, indicate that ground temperatures rose 0.4C over the past decade, four times faster than they did in the previous century…”
    “For the high-emission scenario, the area with permafrost in any of these layers shrinks from 4 million to just over 1 million square miles by the year 2050 and decreases further to about 400,000 square miles (1 million square kilometers) by 2100. In the low-emission scenario, which assumes major advances in conservation and alternative energy, the permafrost area shrinks to about 1.5 million square miles by 2100.â��

    Given all this information, perhaps Roger Pielke Sr. should revist his 2005 statement: “Our conclusion is that the Arctic Systems Science report, which received so much media attention, significantly overstated the actual trends of Arctic sea-ice coverage.”

    This report, available at, should be required reading for any journalist working ‘the climate beat’. (at least read the conclusions!). Journalists should also stop relying on a small clique of contrarians (who have been proved wrong time and time again) for sound bites. I suspect that what happens is that editors direct journalists to ‘appropriate experts’ as deadlines loom – but that’s poor journalism, and also results in a public perception that there is still any significant debate on the basic issue. Spinning articles using terms like “emotional debate”, “climate heretics”, and so on is also a disservice to the public; the issues involved are scientific in nature, not emotional or religious.

  36. Henry:

    I don�t suppose the corporate stool pigeon who wrote that idiotic piece on the arctic being free of ice for white boys in sailboats considered what the fate of polar bears and other life beyond the cushy confines of pseudoscientific journalism in London will be? Or where all this melted ice is going to go, maybe in New York, bigger hurricanes?

  37. Charles Muller:

    I suggest everybody should read ALL conclusions of ALL climate scientists, not just those which comfort his/her own’s opinion.

    For example, I don’t think current models and observations of permafrost enable us to say if thawed zones will be source or sink in the carbon cycle of the coming decades. As far as there are preliminary but contradictory results (eg Payette 2005 or Christensen 2004), we should be more careful before any statement on positive feedbacks. Broader assessments (like PErmafrost and Carbon Emissions – PEACE) will be useful.

    (For methane hydrates, I didn’t read any alarming projections since Kennett et al. 2003′s piece – in my opinion, Schmidt et Shindell 2003, Sowers 2006 or McDonald 2006 conclusions didn’t really favour the worst scenario hypothesis).

  38. pete best:

    Dear RC

    Figure 4 possibly shows the current arctic ice line (red) on the lower side of the mean model which you can see from figure 2 to. Is 2040 the earliest that the the artic sea ice will be clear in the summer ? Could it not be even earlier or do energy constraints or ice albedo feedback be a limit on how early it can be.

  39. Mark Hadfield:

    Great post Cecilia.

    Would you care to take a look at this article on John Fleck’s blog:

    He says

    “In the news release, only the ‘ice-free in 2040′ model run is discussed. It is the model run featured in the animation included with the news release. Is it any surprise that this is the scenario journalists chose to focus on, given that this is what the scientists, through their news release, told them was the most important?”

    Would you like to comment on this?

  40. Grant:

    Re: #34 (William Astley)

    You say

    The planet was roughly 2C warmer, 8500 years ago, as compared to current temperatures.

    What’s your source for this claim? Graphs published by James Hansen indicate that we’re soon going to cross the temperatures in altithermal (the 8500 yr ago period you refer to) and Eemian (the previous interglacial) times. This graph also casts your claim in doubt:

  41. Hank Roberts:

    David Archer has a recent summary article:

  42. Ike Solem:


    The permafrost has been an inert member of the global carbon cycle; one could get at the age of the carbon locked up in the permafrost by looking at the 14C radioactive isotope content (and having just checked, there is indeed a substantial literature on this very topic) – for example, see While there is no evidence that any person has ever eaten the flesh of frozen mammoths, microbes will not be so particular. To quote from the cited abstract, “Our results indicate the potential for ancient C to fuel microbial respiration and C release once permafrost Yedoma soils are thawed”.

    It is highly unlikely that the permafrost will become a sink for global CO2 as warming proceeds. For a ScienceDaily news report, see Greenhouse Gas Bubbling From Melting Permafrost Feeds Climate Warming” Whether it is methane or CO2 that is released will probably depend mainly on the local hydrology; wet conditions favor more anoxic conditions which favors methane release.

    A good article on the potential effect of increased CO2 on carbon sinks (photosynthesis) can be found here. Note that plants are also very sensitive to extreme weather events (a searing but short-lived heat wave can have a dramatic effect on the yearly agricultural yield, for example – something that is hidden in yearly avg. temps). There is really no evidence that a “CO2 fertilization effect” will mitigate atmospheric CO2 levels or lead to increased agricultural productivity, despite what some fossil fuel-funded ‘research centers’ would have you believe.

    On the issue of methane clathrates, it might be worth considering where the heat to melt the ice is coming from. In the 1999 Rothrock et al paper, they point to ocean currents, atmospheric poleward heat transfer, and downwelling radiation as the possible conduits. A warming Arctic ocean might lead to methane clathrate release, though the response time is probably over a century or more (see this 2004 report on ocean temps and global biogeochemistry ) This is why we need to take action now, not at some unknown point in the future.

    Finally, you can always find scientists who will uphold the contrarian position in any scientific debate – as a good example, one can find PhD’s who will tell you that AIDS has nothing to do with the HIV virus – but it would be a serious mistake to base government policy on such claims. When we read media articles on the ongoing AIDS epidemic, no journalist feels the need to include statements from ‘the other side’. The relationship between increased temperature trends, climate change and human carbon dioxide and other greenhouse gas emissions is of a similar certainty.

  43. Nigel Williams:

    I note that all the models show a decline in ice extent, with the middle order models dropping below 50% (6 million sq km) by 2050.

    By this stage (50%) I would think that the entire ice cap has become detatched from tera firma and is floating around at the mercy of wind and currents.

    Depending on surface circulation one can imagine the residual ice cap sort of sliding off the pole and heading into the Atlantic…?

    How do the models view the effects of the remaining ice cover floating away from the polar regions into more southerly regions that favour melting, rather than them staying obligingly close to the pole and away from higher solar insolation and warmer current areas?

  44. Hank Roberts:

    >34, 40
    Lamb? Tree stumps?
    He may have been looking at something like the Medieval Warming, a local not a global condition; the more modern work tries to account for anecdotes in the larger context.

    Lamb,H.H., 1972 and 1977, Climate: past, present and future: London, Methuen, volume I 613 pages, volume II 835 pages.

    Lamb,H.H., 1982, Climate, history and the modern world: London, Methuen, 387 pages.

    Someone at CRU may be able to put that into context.

    “Back in the 1960s, all seemed stable with the world’s climate, and no-one had heard of ‘global warming’, until pioneering climatologist Hubert Lamb began to establish climate change as a serious research project. ”

  45. Nigel Williams:

    …and is the loss of ice cover likely to lead to any significant change in ocean circulation through the polar regions, or is the water depth below the existing ice cover such that circulation will continue virtually unaltered?

  46. Charles Muller:

    #42 Ike, permafrost is not the central subject of this discussion, so I won’t insist on it. But I think you should balance more carefully what is “highly unlikely” or not. Recent papers like Zimov et al. perspectives in Science 2006 are still a bit speculativeâ��and carbon cycle models still in their infancy.

    #40 For Western Artic, some recent works suggested a warmer than present condition. See for example Kaufman et al review in QSR :
    That’s why I ask in #6 if we have any information about summer sea-ice extent for this period (and LIG, July answer in #23). More broadly, I’d like to know if sea-ice reacts in the same way to orbital and GHGs forcings in current models and if not, what are the main differences in ice behavior and/or the main drivers in present and future ice melting (see also Judy questions in #24 for a much more precise context).

  47. Eric Swanson:

    Re: #20

    Dr. Bitz, thanks for the pointer to the CCSM3 documentation. I had looked at it, but not gone back and carefully studied Briegleb, et al., 1986.

    I had taken a look at Scott Pegau’s data, plotting each day’s worth, however, I have not seen his paper in which he documents the results. I will need to find a copy to see whether he compared direct and diffuse radiances. His archived data shows that he made his measurements at times near local noon in mid-summer, when the sun was rather high in the sky. There was only one day with a full 24 hours of measurements. Also, he noted that there were problems with ice formation on the instruments, as there were with the other station instruments. Lastly, he used different types of instruments for measuring the downwelling and upwelling energy, which could be a further source of errors. Since SHEBA, there is new information about the Eppley PSP type pyranometers, pointing to a previously unknown temperature impact on their output.

    Re-reading Dr. Holland’s e-mail, I note that what she suggested was that the sea-ice models were in need of improvements, as Judith Curry also pointed out in #24 above.

  48. Ike Solem:

    RE#46, #40, #34

    Charles – the statement being questioned was “the planet was actually 2C warmer 8500 years ago” and the paper you reference is a review of a temperature maximum in the western Arctic, robustly supported by a lot of paleoclimate data. The western Arctic is not the planet! Having actually flipped through the paper, I was struck by their final statement:

    “Unlike early Holocene warming, however, future warming will not be counterbalanced by the cooling effects of a residual, decaying North American ice sheet.”

    That ice sheet was the Laurentide ice sheet, a remnant of the glacial past – and one might also add that the Greenland Ice Sheet looks to go the way of the Laurentide in the near future. This is typical abuse of scientific publications by climate contrarians.

    In any case, warming the Arctic will affect both permafrost and sea ice – and then there was Ward Hunt Ice Shelf – just because you see icebergs doesn’t mean the planet isn’t warming.

    Regarding permafrost, there are many publications indicating that the newly exposed Siberian regions were a net carbon sink in the early Holocene, as peatlands rapidly developed – but that was between 11.5 and 9 thousand years ago as the world was coming out of a glacial period. For example, see here and links contained – but you’re not going to claim that’s evidence that the permafrost will act as a carbon sink in the modern world?

    In case you were going to, here’s the current situation (1993 Nature paper): Recent change of Arctic tundra ecosystems from a net carbon dioxide sink to a source. Note – Siberian lakes are disappearing.

  49. Cecilia Bitz:

    Sorry I can’t answer every question. I appreciate the scientists who
    have shared their expertise in this discussion and answered many
    questions far better than I can.

    Comment 12 Will sea ice continue to thin at 10cm per year even if the
    CO2 levels are held fixed at 2000? No, assuming there are no
    unforeseen tipping points, the thinning rate would slow down due to
    stabilizing effects. In fact, the thinning rate slows down in CCSM’s
    A1B scenario, even though the CO2 level continues to rise. Retreat
    accelerates, but thinning decelerates in our A1B scenario.

    Comment 14 How is the North Pole displaced into Greenland? Just as
    longitudes (or meridians) converge at the real NP, the width of grid
    cells converge in a model that is square with real longitudes and
    latitudes. This is undesirable, so this model’s NP is displaced into
    Greenland, and the grid cells are NOT square with real latitudes and

    Comment 24 Judy – Thanks for your comments. Oversimplified is not the
    same as missing though. The items you list that contribute to
    ice-albedo feedback are parameterized in the model. I am not sure that
    more sophisticated physics would yield higher sensitivety. Among the
    items you list that are totally absent from models, I don’t think any
    are strongly amplifying or stabilizing. Nonethesless, we are already
    working hard to improve the model physics for IPCC AR5, so one day we
    should know for sure. I am curious why you have a hunch that the
    transition to an ice free arctic during summer might be slowed?

    Comment 39. Why did our paper focus on an extreme case? In a paper
    _about_ rapid ice retreat, it is not unreasonable to highlight the run
    with the most extreme reteat. I am grateful to have this opportunity
    (in addition to the paper) to discuss other model results
    and the uncertainty in the magnitude and frequency of rapid ice
    retreat. I don’t think it should be surprising that a press release
    from NCAR would focus on the NCAR CCSM results, the model Dr Holland
    and I helped develop over the past decade, rather than other IPCC AR4

    Comment 43. Can sea ice slip into the North Atlantic as the
    concentration declines? Probably not catastrophically. About 10% of
    the ice volume is exported into the North Atlantic every year
    today. The rate depends on the ice velocity and the thickness. The ice
    can move faster as it thins, but there is an upper limit set mostly by
    the wind speed. Most models compute ice dynamics today and they
    account for variations in the export rate. Frankly, I don’t remember
    whether the export increases or decreases in the future in CCSM. Dr
    Holland would know.

    Comment 45. Does the Arctic Ocean circulation change? It does in
    CCSM. Relatively warm water circulates into the Arctic Ocean from the
    North Atlantic. At present this current travels near the surface until
    it splits around Svalbard (the islands between the northern tip of
    Greenland and Norway) and then subducts below the surface, remaining
    well isolated from the sea ice in most of the Arctic Ocean. In our
    model this warm current stays nearer to the surface a little further
    past Svalbard on the eastern branch in the future. There are other
    more changes, but I mention this one because it affects ice

  50. William Astley:

    In reply to comment 48: Muller’s referenced paper supports Lamb’s text book which states that the warmest period in the arctic occurred roughly 8500 years ago, at which time the average temperature was 2C warmer than the current climate (As noted Lamb’s text book includes a picture of tree stumps that are 200 miles north of the limit of the current arctic tree line.) The following is a quote from the paper in Muller’s comment (I include a link to the Holocene maximum temperature paper below).

    “The timing of the Holocene Temperature Maximum varied spatially, but the increase in temperature… At the 16 terrestrial sites were quantitive estimates have been reported (mainly summer estimates) were 1.6C +/- 0.8C higher during the HTM than present.”

    As to the quote “Unlike early Holocene warming, however, future warming will not be counterbalanced by the cooling effects of a residual, decaying North American ice sheet.”

    Unfortunately its appears planetary warming is about to end and the planet will suddenly cool which seems ironical as all of the discussion in the forum centers on catastrophic warming.

    I must be the only person in the forum who has read the GCR papers, read the solar papers that discuss the current southern coronal asymmetry of the sun, who has looked at solar data that supports the fact that the sun is at its highest activity level in 8000 years, who looks at the current solar data (see coronal hole CH255 and data Dec. 16 in the attached link) or who has examine paleoclimatic data outside of “recorded times”. “Recorded times” Gavin notes is the last 150 years.

    I must also be the only one who has investigated the data concerning geomagnetic field changes (cyclic 60 degree changes in inclination and dipole magnitude, starting about 800kyr ago, which coincidentally coincides with the end of the 41kyr glacial cycle and the start of the 100 kyr glacial cycle.).

    I am now looking into the question as to what is the source of geomagnetic field and why would the geomagnetic field suddenly and periodically change. I have unfortunately found the solution to that problem. Unfortunate as it supports the sudden cooling statement.

    Solar Terrestrial Activity

  51. Edward Greisch:

    Reply to 34 William Astley: Are you saying that you are in Favor of anthropic global warming?

  52. Dmitry Vyushin:

    Dr. Bitz, thank you for your review. I knew about your paper but didn’t have a chance to read it. Last November I heard a talk by William Merryfield at CCCMA in which he mentioned that CGCM model also has some runs with abrupt Arctic sea decline similar to the one shown in Fig. 1a. His paper “Merryfield, W.J., M.M. Holland, and A.H. Monahan: Multiple Equilibria and Abrupt Transitions in Arctic Summer Sea Ice Extent” is under review now in Journal of Climate.

    I have a question for you. Why are GFDL models are missing in Fig. 4 ?

  53. Timothy:

    Further comment on question at #43

    If you look in Fig 1, above, at the sea-ice concentrations in the latest decade, you can see that the remaining sea-ice is concentrated along the Greenland coast, so it is not centred on the North Pole and would not become detached in one big cap as you suggest.

    So we don’t have to worry about that.

  54. Victor Amoroso:

    I would like to know how you developed your model for climate forecasting. You seem to have left many things out, such as the oceanographic event known in layman’s terms as the Global Conveyor Belt. Increased fresh water from melting ice caps (decreasing salinity) would stop this process, and thus prevent heat movement from tropical latitudes towards the poles. This would halt all ice loss and bring about a period like the Little Ice Age (there is some thought that this process caused this historical event).
    However I digress. Unless you eliminated it for brevity in your article, you make no mention of any other climate variables other than CO2, which quite possiblily is not the most important greenhouse gas, and albedo, which few think is a major dipping point in global temperature. Your article makes little mention of the thirty plus other factors that make up the climate. Due to this fact alone I would have to say that your models are statistically impossible.
    Thirdly, with our current level of technology, it remains impossible to accurately predict the weather more than 10-15 days out. One might say that weather is a complex monkey and this fact makes longer term forecasting difficult. Climate, even over such a short time as two weeks, is more complex than localized weather patterns. Since it operates over a longer time scale, this compounds the difficulty beyond measure, as any error in variables is obviously magnified as the model progresses. Therefore, trying to predict climate over the short period over 100 years (a small chunk of geological history) is about as accurate as a two-week old weather prediction. No weatherman is that good.

  55. Alastair McDonald:

    When the multi-year ice has gone then that store and source of fresh water will be lost from the Arctic, so raising its salinity and lowering its freezing point. Thus seasonal ice formation will become more difficult once the multiyear ice has gone.

    Moreover, without ice in the Arctic during the summer, then the sea temperature will not be held at freezing point by the melting ice. The resulting higher sea temperatures will further inhibit the formation of winter ice.

    It is the presence of the multiyear ice which gives the Arctic basin a continental type of winter climate. Without that ice, then there is a strong possiblity that no ice will reform in winter.

    With an average summer ice thickness of 2m in 1997 and a melt rate then of 0.1 m per year (Cecilia is wrong thinking that Rothrock et al. 1999 did not adjust their measurements for the time of year,) it seems highly likely that the latest date that the summer ice could disappear from the Arctic is 2017, not an earliest date of 2040.

    I suspect Judith knows that, and it is why she is pleading for Cecilia to come up with a negative feedback which would make this prediction invalid.

    Judith mentioned ridging as one possible negative feedback, but as the ice thins ridging will decrease. Thus when the ice does melt it will do so over large areas since it is evenly spread over the ocean surface. This means its demise will be abrupt.

    We are already seeing how the late formation of the Arctic ice this year has led to warm winters in the Northern Hemisphere. Here in southern England daffodils are blooming which normally come out in late March. This is not a slow warming from a gentle increase in CO2, but the beginning of an abrupt change. The sooner scientists face up the the fact and warn the public of the dangers, then the sooner some defensive action can be taken.

  56. Neil Thomas:

    Shrinking the forecast window


    From a purely laymans point of view, I only have one issue with the article. You find that if you take 2.5 dacades worth of data, you get an arctic ice free in 2110. If you take one decades worth of data, which enhances the rapid acceloration effect we are seeing, they you get dates ranging from 2040 to 2055.

    As I see it if you take data from the last two years you are going to get a forecast somewhwere around 2020 for Ice free. Where do you stop?

    This year the Arctic ice reformed later than normal and in fact Svalbard still has less ice around it than in November 2005 during the 2005-2006 winter when ice regrowth was “surprisingly low” in the winter. This tends to lean towards a tightening cycle as has been seen over the last 5 years.

    Had it not been for the low August temperatures in 2006, there would have been another record low in sea ice extent. However even with the August cold snap there was fractured ice and open water right up to the pole itself. Are you sure there will not be significant open water there in 2007 and if there is, what does this do to even the most pessimistic projections you have?

  57. Leonard Evens:

    Re 55:

    Mr. Thomas seemed to have missed one of the main points. The prediction is not based on linear extrapolation from observed trends, which the commentary explicitly said would yield a misleading result. It is based on averaging many runs of a climate model, if I understand correctly. The relevance of the observed record is that the climate models’ results are in reasonable agreement with that record.

  58. pete best:

    Dear RC

    in RC’s last article concerning consensus scientists not being alarmist enough for the media we get the media focusing in on the worst case scenario here because it is only worst case scenarios that resonate with the public and make anyone want to do anything about it. If scientists insist on the objective truth being told then they must also shoulder the blame when nothing gets done about AGW. This is the price scientists must pay for anything being done about it, worst case scenarios apply although when it comes to peer reviewed work it be set within a objective framework and be scientific.

    Maybe Lovelock and some other media climate writers have it right, scare the public otherwise nothing will happen.

  59. Ron Taylor:

    Re 53

    Victor, please do a little background reading on this site before making such assertions. Sigh…

  60. Judith Curry:

    Re #49 Cecilia, calculations that I made a while back indicated that it was very difficult to completely melt the very thick ridged ice near the canadian archipelago

  61. Alastair McDonald:


    It may be difficult to melt the ridges using in a model, but judging by this concentration map for last October 10th, there seems little possibility for ice ridges to the north of Greenland, the Canadian Archipeligo, or anywhere else for that matter See for the key to the colours.

  62. Nigel Williams:

    Re #58, Pete, we should, I believe, continue to expect our scientists (as RC) to tell us the truth, as much of the truth they know, and nothing but that truth, including the uncertainties, and the range of best to worst possibilities. It is then for our politicians to take the lead from that information and prepare prudent and reasonably affordable contingency plans to reduce the risk of significant economic and social impacts from the predicted range of events.

    We simply have to keep laying these truths out in front of the political system and patiently wait for the political proces to run its often miserable course. The scientists must avoid at all costs the taint of exageration for effect.

    Our role as citizens of our respective states is to directly and earnestly encourage our politicians at local levels to take heed of these truths and to act upon them in a way that gives us some genuine hope of a safe, or at least of a survivable future.

  63. Mark Hadfield:

    “Comment 39. Why did our paper focus on an extreme case?”

    No, the question was: Why, when the abstract and press release specifically mentioned the “near ice-free September conditions by 2040″ event, do you express dismay (above) that this was highly publicized?

  64. Aaron Lewis:

    I look at the daily ice maps, and they tell me that warm salty water from the North Atlantic is flowing into the Arctic.

    My guess is that there already is enough “heat” and salt in the Arctic basin to melt all the sea ice. All we need for the sea ice to go â??poof,â?? is a bit of mixing to disrupt the layer of low salinity water directly under the sea ice. Such mixing could come from turbulent flow, convection currents, or storm driven mixing at the edge of the diminished sea ice. Do the climate models understand the physics of ocean currents, or do the models assume that some configuration of ocean currents observed in the past will persist into the future?

    Once the sea ice no longer protects the low salinity surface waters from storm mixing, refreezing is more difficult.


  65. Barton Paul Levenson:

    Re “I would like to know how you developed your model for climate forecasting. You seem to have left many things out… …Your article makes little mention of the thirty plus other factors that make up the climate. Due to this fact alone I would have to say that your models are statistically impossible.”

    She was modeling Arctic ice cover, not the whole climate system.

    “Thirdly, with our current level of technology, it remains impossible to accurately predict the weather more than 10-15 days out.”

    You may have missed the difference between climate and weather. Weather is, indeed, complex and hard to predict very far out. Climate is a long-term average. To illustrate the difference, I don’t know what the temperature will be in Cairo, Egypt tomorrow. But I can be fairly safe in betting that it will be higher than the temperature in Oslo, Norway.

  66. Pekka Kostamo:

    How about this: The second largest of the world glaciers will disappear. It will be replaced by a whole new ocean.

    “Arctic Ocean” was a mapper’s mistake, in fact. It will become reality. Not only the albedo will change, everything else will as well, in the surface/air interface. Could well qualify as a “tipping point”.

    SH will not experience the same drastic change, with probably some more interesting unstability effects.

  67. llewelly:

    Pekka, it is not clear what you mean by ‘The second largest of the world glaciers’ . If you mean the Greenland Ice Sheet, yes it is likely melt, but that will require several centuries. Furthermore, nearly all of the Greenland Ice Sheet is grounded far enough above sea level that it will not in any sense ‘be replaced by a whole new ocean’ . Rather, it will act to raise the level of the existing ocean.
    If on the other and you mean the West Antarctic Ice Sheet, the WAIS is indeed grounded below sea level, and therefo potentially subject to more rapid collapse than the GIS, but the WAIS is colder and better protected by local climactic conditions; melting the WAIS requires an extent of global warming that is still readily avoidable. Whether or not the group of islands and peninsulas that would be uncovered by the melting of the WAIS could be called ‘a whole new ocean’ is debateable.
    If on the third hand you mean the arctic sea ice, that is by no means a glacier, though a disappearance or great reduction of said ice would change the Arctic ocean a great deal, and also change the NH , and, to a lesser extent, change the SH.

  68. Steve Bloom:

    Re #60: Judy, it appears from the paper that “near ice-free” means with some ice persisting in the archipelago area:

    “After this event, by 2040, a small amount of perennial ice remains along the north coast of Greenland and Canada, leaving the majority of the Arctic basin ice free in September (Figure 1b).”

    I’ve seen similar results elsewhere, and had always assumed that this was because the archipelago ice is not subject to warming from currents in the same way open sea ice is. Is that consistent with your work? In any case, it’s not clear from the remarks above that there’s really a contradiction.

  69. Ike Solem:

    Just to recap: the long-standing computer model predictions of rapid warming in the polar regions are all being confirmed; the diminishing Arctic sea ice extent, the melting permafrost and the melting Greenland Ice Sheet are all well documented at this point. You can also listen to what the Inuit have to say about this.

    See also for some nice photos of what meltwater rushing into a glacier looks like, as well as a good discussion of the issue, for example:

    “The faster ice flow, ice thinning and consequent lowering of the surface elevation of the ice sheet can open a feedback to more melting that has not been considered in computer models that predict ice sheet response to climate change.”

    Yes, better data is needed – which is the mission of CRYOSAT-2 …all while the US has cut funding for climate satellites in favor of putting another person on the Moon???

    Given the recent discoveries regarding the Greenland and West Antarctic Ice Sheets, it’s hard to say exactly what they will do, particulary as polar summers get warmer and warmer, other than that the older predictions of melting time are shortened by some degree.


    Very often it is written in media that with the anticipated global warming the sea level will incease. This increase is implied to be caused by the melting of the north pole icebergs and ice layer.

    However, with simple calculation it can be shown that when a blog of ice in a container of water melts, the level of the water in the containes remains constant.

    I would anticipate that the sea level would rise due to the melting of snow and ice in the continents.

    Any comments on this?

    [Response: Sea level rise is from thermal expansion of the ocean, and melting snow/ice on the continents. This is scientifically well known; you can generally expect the media to get things wrong, though - William]

    Another point is that there is a lot of discussion for the changes in the north pole but not much on the south pole. Is there any reason for this?

    [Response: The arctic is more exciting :-) though you can try this - William]

  71. Neil Thomas:

    Perhaps I am missing the point. However MY point is that every model, including this one is failing to predict the severity of the change. No model predicted the 2005 melt back or the sustained melt in 2006. 2007 is likely to be even worse than 2005 unless we get a cold summer.

    It’s kind of going over the same map again and again in the same way to see if we can find a better route to our destination. Unfortunatley directly between our start and destination there’s a great big hole in it. It’s a whole called knowledge.

    Observation shows there is no way that we will be Ice free in 2110 or even 2060. The model shows we will have ice until either depending on the model you follow.

    The curve is getting steeper but the inclination of the scientists is to even the curves out so that we can get the best fit picture.

    Perhaps we should go with the curve just once and see where it leads. We might learn something.

  72. Matt:

    All the way back to #28, sorry. The reason you are getting more pollen in the air is due to favourable growing/seeding conditions. When you get less pollen in the air then start worrying. Your hay fever is hardly a topic of concern. that is the good news about global warming, the bad news is that there is always the possibility the pollen and seed will hit barren arid ground and be unable to grow.

    But then again don’t worry the whole lot was probably going to rot and produce methane anyway :)

  73. pete best:

    Re #62, if the political world responded to scientific advice only then the world would already be curbing carbon emissions from fossil fuels but that is not how it works unfortunately. Politicians are opportunists and the media want us to watch stuff and read newspapers etc so over the last x years the message from the press has to be hyped in order to get our interest and then mobilise us to influence politicians.

    The USA media is still split along very traditional lines (left and right) on climate change and many people over exaggerate the possible effects or sinply deny them.

    Climate science is unique because it is very difficult for politicians to ask people to cut back by legislation, after all in the west scientific and technological progress is everything these days. Therefore even though the evidence is scientifically overwhelming this is not what science is supposed to do for us, ask us to cut back and reduce progress so that people cannnot drive and fly and consume with impunity.

    Fortunately many people seem to think that it is possible to cut carbon emission enough without sacrificing progress, however I am doubtful of this and politicians are somewhat paralysed by what to do, hence the stern report and the like that can galvanise industry to start thinking seriously about what alternatives to fossil fuels there are and what can be done. However do not be mistaken, fossil fuels are energy dense and humankind is likely to consume the lot including coal although maybe at a reduced rate until some kind a miracle liquid alternative is found and put into production so the planes can still fly and the cars still drive.

    Lets hope that hydrogen or type II ethenol work out in some major way but as yet humankind has not even begun to look at the issue in earnest yet.

    China, Brazil and India pose the greatest threat as they are growing and are using the same technologies are we are. All the news about renewables is great but only touching <1% of current fossil fuel energy use.

    My main issue is time and if the left wing media exaggerate and demand action with alarmism stories of disappearing ice shelves, rising sea levels, drought, famine and more extreme waether then so be it I say. The press always hype things anyways.

  74. pete best:

    In fact the issue is worse than anyone can imagine with regard to alternative energy and even efficiency gains in the grand scheme of reducing CO2 emissions to a noticeable effect.

    MIT presentation on the future of energy and how to deal with climate change.

    30 years to roll out a new energy technology en masse and the growth of energy use and the addiction to fossil fuels makes it all a bit scary.

  75. Eli Rabett:

    Pete, how long do you think it took to roll our coal/steam, petroleum and natural gas? The length of time is sufficient.

  76. pete best:

    Re #75, it has taken 150 years to get where we are today globally.

  77. John L. McCormick:

    RE # 74

    Pete, it is more than [all a bit scary.]

    The sunk costs of US electric generation have beeen made to meet consumer demand growing about 1.9 percent per year. In 2005, about 4 trillion Kwhr was US demand and that contributed about 2.44 billion tons of CO2 to the atmopshere.

    The top five CO2-emmitting electric power companies emitted 722 million tons or about 30 percent of the industry total. That is not good news.

    The cost for any of those companies to retrofit their generation base would be measured in the hundreds of billions of dollars and their customer base is probably struggling now to keep up with electricity costs.

    Trying to sort out a response to global warming means we also have to do the numbers. They are frightening.

    A 1.5 MW wind tower needs about 163 tons of steel and 100 cubic yards of concrete just to set it upright. And, it has about a 40 percent on-line capacity.

    I will stop there. It gets too depressing.

  78. Ike Solem:

    If there’s pollen in the air in the middle of winter, it means a lot of plants are responding to warm conditions and are flowering early – if you are trying to imply that ‘global warming will be good for plant growth’, you are wrong; rather what you will see as a result of heat waves and other energetic weather events (i.e. climatic instability) is a general decrease in agricultural yields. On the other hand, a large-scale program to plant trees in favorable locations would result in some storage of CO2 in the form of wood – but it’s also necessary to stop burning fossil fuels.

    Imagine that all access to fossil fuels was suddenly cut off – what would happen? There would be immediate changes in agricultural practices, and solar panels and wind turbines would suddenly be in very high demand. Consider Honda’s new solar factory, which has a production capacity of about 27 Megawatts (solar power panel output). In contrast, one of the largest coal-fired power plants, the 4 Corners plant in the Southwest, can output 2000 MW of power. Thus, it would take Honda’s plant about 75 years to produce enough solar panels to replace this facility – but if there were 75 such plants, it could be done in one year. It’d probably be best to install the panels on people’s homes.

    Honda’s plant cost $100 million; 75 plants would cost $7.5 billion. By contrast, a single aircraft carrier costs $4-5 billion. Thus, to make the switch to renewable energy would require a massive effort – but it is technically and economically feasible, especially if one considers the long-term alternatives. We should also be putting several billion dollars a year (at least) into renewable energy research.

    Increased energy efficiency across the board will also result in huge reductions in power demand; see these predictions for California from NRDC.

  79. yartrebo:

    Re #70:

    “However, with simple calculation it can be shown that when a blog of ice in a container of water melts, the level of the water in the containes remains constant.”

    The calculation isn’t so simple, and the water level will rise slightly. Sea ice is less salty than sea water, and thus the ice displaces slightly less sea water than is produced by melting it, and the water level will rise slightly.

    As for your little experiment, try melting a block of ice in a container of salty water and be very careful with the measurements (the effect isn’t all that large).

    Does anyone here know what the effect of melting the world’s sea ice would be on sea levels? Would it even be measureable?

  80. yartrebo:

    Re: #74

    “30 years to roll out a new energy technology en masse and the growth of energy use and the addiction to fossil fuels makes it all a bit scary.”

    Even scarier is that 30 years is an optimistic forecast. The latest craze in energy generation is pulverized coal power plants. Once the world gets serious about global warming, 30 years might not be too bad an estimate, but the clock is ticking backwards at the moment.

  81. John L. McCormick:

    RE # 74
    Pete, it is more than [all a bit scary.]

    The sunk costs of US electric generation have beeen made to meet consumer demand growing about 1.9 percent per year. In 2005, about 4 trillion Kwhr was US demand and that contributed about 2.44 billion tons of CO2 to the atmopshere.

    The top five CO2-emmitting electric power companies emitted 722 million tons or about 30 percent of the industry total. That is not good news.

    The cost for any of those companies to retrofit their generation base would be measured in the hundreds of billions of dollars and their customer base is probably struggling now to keep up with electricity costs.

    Trying to sort out a response to global warming means we also have to do the numbers. They are frightening.

    A 1.5 MW wind tower needs about 163 tons of steel and 100 cubic yards of concrete just to set it upright. And, it has about a 40 percent on-line capacity.

    I will stop there. It gets too depressing.

  82. Louise:

    I am aware of climate change (I still think it is different than global warning). I am fairly ignorant of the science to measure climate change (hence my reading these comments, but I would like to know how many of you drive a car?

  83. pete best:

    Re #81, the MIT report seems to suggest that ethenol is a good be for a gas/oil/petrol/diesel replacement, well 40% of it anyway which is something. It is as you say difficult to see the energy wood for the tress and there is no real clear cut answer here.

  84. Charles Muller:

    Rothrock 1999 evaluations are discussed, ice thickness depends of a lot of factors, and you shouldn’t expect a linear trend. About thinning of the Artic ice, have also a look at Winsor 2001, Tucker 2001, Holloway 2002, Polyakov 2003, Laxon 2004.

    Holloway, G., Sou, T (2002), Has Arctic Sea Ice Rapidly Thinned?, Journal of Climate, 15, 1691-1701.
    Laxon S. et al. (2004), High interannual variability of sea ice thickness in the Arctic region, Nature, 425, 947-950.
    Polyakov I. et al. (2003), Long-term ice variability in Arctic marginal seas, Journal of Climate, 16, 2078-2085.
    Tucker W. (2001), Evidence for rapid thinning of sea ice in the western Arctic Ocean at the end of the 1980s, Geophysical Research Letters,, 28, 14, 2851-2854.
    Winsor, P. (2001), Arctic sea ice thickness remained constant during the 1990s, Geophysical Research Letters, 28, 1039-1041.

  85. Dan:

    re: 82. I think the point is that there are many things that people can do to minimize use of fossil-fuels, let alone use alternatives. CO2 emissions from fossil-fuel power plants are the primary emitters of CO2. With regards to cars, the key is to minimize use and maximize fuel economy. Obviously, hybrids are good examples of clean emitters. I believe the average annual miles driven in a family car in the US is probably 12,000-15,000 per year; I am sure someone could calculate what the average CO2 emissions are from such use. In my case, I have kept my annual mileage around 8,000 per year.

  86. Richard Ordway:

    Re. comment 50.


    Can you please state references for any of your assertions from published peer-reviewed journals?

    If not, you should try to get your data published in them.

    That is the correct place where the whole world will evaluate its validity.

    There have been studies published in peer-reviewed journals which have debated various aspects of global warming studies such as Von Storch and Lindzen.

    Even global warming was at first a very contrarian view when published in the 1800s…but it was still published when the evidence was there…

  87. Lynn Vincentnathan:

    Some have commented that cooling is more dangerous than warming, and perhaps that is so for humans, but according to Lovelock’s REVENGE OF GAIA, a cooler climate is actually better for life in general (I’m not sure if that’s accepted broadly in the scientific community, but I found his arguments fascinating).

    Re #3 & #7, & how does this Arctic ice melt impact the world, yes, that is an important question, and it seems in many ways, in addition to decreased albedo & more warming & melting permafrost and clathrates.

    I’ve heard that the Arctic ice serves as sort of an “air conditioner” for mid-latitudes during the summer. I don’t know if that’s accurate or over-simplistic. But if so, then without that “air conditioner” we might expect a magnification of the heat in the summer (beyond the more straight forward warming from global warming) & more heat deaths & crop failures (from the excessive heat).

  88. Ark:

    #81: John,
    I fully agree that we have to “do the numbers”, but what’s so depressing about your wind turbine numbers? The amount of primary energy to produce your steel and concrete is approx. 5,000 GJ (GigaJoule), heavily dominated by the steel (I’ve taken 30 GJ per tonne). This is equivalent to the primary energy saved by the turbine in its first 2 months of operation (400 full load hours, 40% efficiency of fossil power generation).

  89. Ike Solem:

    This is a bit off topic, but since renewable energy is the only rational response to global warming, and since the claim has been made that ‘it will take 30 years at least’ and that ‘the situation is frightening and depressing’, consider this:

    In October 2006 the US imported 10 million barrels of oil per day at a cost of around $60 per barrel.

    That would be a total cost of 18 billion dollars for the month of October alone; if we include natural gas imports for October 2006 (about one trillion cubic feet at a cost of ~$6 per thousand cubic feet) we add on another $6 billion or so for a whopping monthly bill of some $24 billion dollars in global-warming enhancing energy imports. That translates into some $288 billion a year in energy expenditures for imports alone.

    If we were to plow all that money into renewable energy, how long would it take to switch over to a renewable energy-based economy? Assuming that wind turbine systems as well as solar panel ‘breeder’ factories and also advanced biorefineries will cost an average of $100 million each, you could build close to 3,000 such facilities in a single year – that’s one for every 100,000 people in the US – in just one year. Yes, it would be difficult, but not ‘terrifying’ and it certainly wouldn’t take 30 years- and it is the only rational response (along with extensive energy efficiency and conservation practices) to the current situation.

    It would also create untold new jobs, keep dollars at home, and be very beneficial to the US economy. It’s entirely feasible, but it will result in a certain degree of economic upheaval – there’s nothing ‘scary’ about it.

    Geting back to climate science, RE#87 Lovelock’s notion of a cool planet being better for life is really just speculation; life has adapted to all sorts of environments, and all of the major fossil fuel deposits were laid down due to massive biological productivity hundreds of millions of years ago, when temperatures were thought to be quite high. The only ‘scary thing’ is that if we don’t stop burning fossil fuels, we will be heading back to dinosaur times at a very rapid rate.

  90. matt:

    #78 Good one, first of all forests are a crap way to sequest carbon and secondly if all the fossil fuels were cut off they would have no way of transporting raw materials to the building site for windmills etc. logistics suck.

  91. pete best:

    Re #81. Here in the UK onshore wind turbines achieve around 28% and offshore around 31% efficiency, so 40% is a bit high I believe. We are building a 1.5 GW offshore farm near London(for London)requiring some 440 turbines and these are the big ones to. So with those efficiencies and costs of building them, of transport, of build, management and maintenance costs it will take a while for them to perform pay back but surely the life time of these turbines is decades and hence they should prove to be cost effective.

    Another question of course is the number of energy producing hours that a turbine has access to.

  92. Deepak Rughani:

    Dear Dr Bitz / anyone who can answer this Q with certainty

    In last paragraph you state… “If we fix the greenhouse gas and aerosol levels at year 2000 values and run the model into the 21st century, the sea ice retreats for only another decade or two and then levels off”

    Could you clarify if you mean fixing emission levels at 2000 values or atmospheric levels. I initially thought the latter as 2000 level emissions would of course continually increase atmospheric levels (sink absorption just 50 – 60% at 2000 emission levels) and it’s hard to see how ice retreat could then level off…

  93. Alan:

    RE #55: I’m no physisist but an anolog of what you describe (large area’s melting “all at once”) can be seen in a deep fryer using solid oil/fat. As the fryer heats up the oil/fat melts but the surface area remains fairly constant (minor melting at the edge). The layer of solid material floats on a the warmer liquid (like ice in water). The floating layer eventually gets so thin that a sudden rash of random holes appear that rapidly widen, dissolving the large area of solid “all at once”.

    How do I know this? Mum cooked alot of chips.

  94. pete best:

    Re #89, designs and small scale stuff if what you links are showing me. Sure if they can be demonstrated to work and are cost effective then yer great we can hopefully develope, test, build and deply these technologies en masse and reduce CO2 levels to manageable levels. However its a large if at the moment and renewables are not providing much energy at the moment globally that is. This is becasue the world system runs on the notion of fossil fuels and the infrastructure is fossil fuel based. I would be doubful if renewables can displace this political industrial system within less than 100 years espefcially with the worlds appetite for energy being 50 % more within 20 years.

    Another option of course is fusion when it finally yields up more energy out than in but thats a world away at the moment, 2045 at least even to know if its viable.

    The transition to alternative energies will be slow and not fast due to the current world eco political industrial system being what it is. It will happen though as fossil fuels will be getting expensive within 20 years or so people say in the PEAK camp

  95. Nick Gotts:

    Perhaps not sharply focused on this post, but a question I’ve wanted to ask for some time. When ice melts, it takes up heat (80 times as much per gram as required to raise water temperature 1 degree C, if I remember right), and this must cause a cooling in ocean and/or atmosphere. Is this large enough to be a significant negative feedback on a global or regional scale?

  96. John L. McCormick:

    RE # 89, Ike, you said:

    [If we were to plow all that money into renewable energy, how long would it take to switch over to a renewable energy-based economy?] Not very long, I would assume.

    But, wind and solar will not keep the American fleet of 250 million vehicles rolling. And, petroluem provides a minincule portion of electric power boiler fuel.

    Finally, ethanol is not the answer. It is a part of the expanding and complex problem.

  97. Alastair McDonald:

    Re #95

    Melting the ice is a negative fedback on the current warming, but once the ice has gone, without that negative feedback then tempertures in the Arctic will soar.

    However, there is another negative feedback and that is the evaporation of water vapour. At low temperatures the sea will not provide much evaporation but at higher temperatures, when the Arctic has reached 70F or 20C, further warming will be inhibited. But as this 20C rise spreads south, many NH continental regions will become uninhabitable, and food crops will be unsustainable.

  98. Hank Roberts:

    Economists have been talking about how to reduce auto miles driven for some years now.
    Here are just a couple of samples found at the Berkeley Electronic Press, “The Economists’ Voice” — people perhaps worth inviting here to contribute?

    (free w/registration; a subscription offer letter may go out to your institution’s librarian based on your IP address)

    If Voters Won’t Go for Taxing Oil to Conserve Energy, How …?
    Varian, Hal (2006) “Economic Scene, Beyond. Insurance: Weighing the Benefits of Driving vs. the Total Costs of Driving,” [PDF]

    Letter: Pay-As-You-Drive Is More Apt to Reduce Accidents … insurance market. If drivers faced economic …

  99. Steve Sadlov:

    Given the PDO, I have some issues with using 1980 – ~ present as the basis for trend line analysis. Truth is we are still unraveling the PDO (and other cyclical down leg) based decline(s) from 1976 (last PDO flip to positive phase) on, from the overall AGW(ish) decline. Once someone is able to successfully deconvolute the AGW(ish) decline from the cyclicals, then we’ll be talking.

  100. Ferdinand Engelbeen:

    Dear Dr. Bitz,

    There were some issues with modelled and observed Arctic cloud cover in the past.
    Most models underestimated cloud cover in summer and overestimated it in winter. As this gives important constraints to the temperature (more reflection in summer – more loss of heat to space in winter) and melting/refreezing, is this issue solved in your model?

  101. Jim Crabtree:


    One gallon of gasoline weights about 6.2 lbs. It contains about 5.4 lbs of carbon (gasoline is approximately 87% carbon). This one gallon of gasoline produces 19.8 lbs of CO2. This means the average American car (assuming an average weight of 3 500 lbs and 20 mpg) produces its own weight in carbon dioxide in about 12 000 miles. If one takes the carbon cost of refining, transport of gasoline, then the 12 000 miles drops to about 7 500 miles. That is why we have a Prius for our primary vehicle. I also have a small pickup truck (better gas mileage) since I need it for carrying large stuff and it generally gets less than 3 000 miles per year on it.

    When I taught at the University of South Carolina back in the 1980′s, I used to bicycle 9 days out of 10 giving me 10 miles of exercise each day. I actually got my car insurance reduced because of this!

    Jim Crabtree

  102. Barton Paul Levenson:

    Re “Perhaps not sharply focused on this post, but a question I’ve wanted to ask for some time. When ice melts, it takes up heat (80 times as much per gram as required to raise water temperature 1 degree C, if I remember right), and this must cause a cooling in ocean and/or atmosphere. Is this large enough to be a significant negative feedback on a global or regional scale?”

    It doesn’t cause a cooling, just a change of state. Temperature will stay at 0 C until the whole ice object is melted, at which point it will start to rise again.

  103. Steve Bloom:

    Re #92: The reference was to fixing atmospheric levels at the values they had in 2000. Obviously those levels are already history and are far lower than any realistic peak given that emissions are continuing, but the point is that the ice is not irretrievably lost if there are sharp reductions now.

    The question that is begged by all of this (but was outside the scope of the paper) is whether some sort of tipping point may be involved with a loss of ice that includes the entire summer high-insolation season (and thus allows the Arctic Ocean to start picking up some serious heat in contrast to a relatively brief ice-free period centered on the relatively low-insolation equinox) and, tipping point or not, what effect a much warmer Arctic Ocean would have on the Greenland ice sheet.

  104. Ike Solem:


    Burn rubber, not gasoline.

  105. Cecilia Bitz:

    Re #52 GFDL models are missing because they were not yet archived when
    the data were downloaded. They are archived now, but we haven’t gone
    back to get them. It is a lot of work to gather and process the data.

    Re#55 & #84 I said nothing about Rothrock failing to adjust for time
    of year. He’s my colleague, I know he did. I have used his data in one
    of my own papers. You are assuming that the climate is linear, and it
    is not. Dr. Muller – you might also be interested in my paper about
    ice thinning
    from a theoretical and modeling point of view.

    Re #60 & #68 I agree it is difficult to melt the very thick ridged ice
    that piles up each winter against Greenland and Ellesmere Is. This is
    why we considered the last panel in Fig 1 to be essentially ice-free,
    even though there is still some stubborn ice that remains.

    Re#64 Isn’t there enough heat beneath the sea ice to melt it? Yes
    there is enough heat in the Atlantic Layer, which is roughly 500-1000
    m deep. It is isolated from the sea ice by an intevening layer called
    the cold-halocline, which is stabilized by high river runoff and
    Pacific water inflow through the Bering Stait. A paper
    analyzed recent variations in the cold-halocline.
    These layers
    are reproduce in our model and they vary dynamically with the climate.

    Re#71 It is not reasonable to ask a model to predict THE 2006
    anomaly. Look at Fig 2 and you will see that the different ensemble
    members from the model span a large range in just one year. The model
    cannot be expected to predict the spatial pattern of the anomalies in
    individual years, which depend quite a bit on natural variability. As
    stated in the essay, our ensemble of runs agree with the recent
    Northern Hemisphere average trends from the satellite era. It is also
    worth mentioning that if we use the model to estimate natural
    variability (we have multicentury runs at “present day” forcing levels
    from our model while we only have 28 years from observations), then we
    can “detect” a significant trend in the 28 years from
    observations. However, the trend in the last decade from observations
    is not significant.

    Re #79 Robert Grumbine estimates if all the sea ice on Earth melts it
    will raise sea level by 4mm. See his report
    It is pretty trivial compared to sea leve rise expected from
    thermal expansion of land ice runoff (see response to #70).

    Re #92 The greenhouse gas _level_ is fixed, not the emissions. It is
    a senistivity experiment, not a “simulation”. You are correct that
    fixing emissions would still result in rising levels.

    Re #93 Thanks for the analog. I’ll have to try it. The chips are just
    a bonus.

    Re #95 Heat is “absorbed” by melting sea ice and warming the ocean,
    among other things. The ocean, however, has taken up about 7000 times
    more heat than what it takes to melt 40% of the Arctic sea ice,
    according to a recent study by
    Levitus and colleagues
    Ocean heat uptake below the surface mixed
    layer does slow the rate of surface warming. I wouldn’t call the heat
    used to melt sea ice a negative feedback (as noted by #102), but in
    any case, it is a pretty trivial amount of heat compared to uptake by
    the ocean.

    Re #100 Our model overestimates cloud fraction in winter and clouds in
    summer are to thick, so to speak. Every model has biases and always
    will. We are working on reducing this bias however.

    I didn’t want to rag on the media too much here. Overall I was
    impressed by my exchange with reporters. I was dismayed by a couple of
    articles that presented very little detail, especially those that
    appeared to cut-and-paste excerpts from other articles. The worst
    example of these tended only to report “scientists predict ice-free
    summer by 2040″ with no explanation of the context AND two articles
    misspelled my name (this is my fate having a last name one letter
    removed from a bad beer). The more important story for me is about
    the rapid events, which ultimately lead to the 2040 prediction.

  106. Timothy:

    This is a question for Stefan, with reference to his recent Science article. In this you state that: “there are as yet no published physically based projections of ice loss from glaciers and ice caps fringing Greenland and Antarctica.

    I was wondering whether the use of “physically based” was intended to exclude the study by Gregory and Huybrechts []. Is/was there work more simplified, relying on thermal arguments rather than the physical dynamics of the ice cap?

    I had thought that Gregory [and collaborators of] had done some work forcing a specific ice sheet model. Perhaps that isn’t published?

  107. Jim Crabtree:

    Dr. Bitz:

    I have in front of me an article about the results of the meeting of the Canadian Arctic Shelf Exchange Study that took place last year in Winnipeg. Dr. David Barber estimates that the arctic could be ice free in about 15 years.

    I played a little with modeling back in the 1970 for a short while before I decided on a different research area. I look at models as a tool that goes through two phases. Phase 1: Does the model show that I understand the problem? Phase 2: Once the model shows I understand the problem, then I can use it for research into the unknown.

    I really question whether the current models are to the state where they can be used for prediction when there are so many “butterflies” out there and some of them are probably big “butterflies”. (For example – models that treated the Greenland ice cap as a solid mass).

    As I have taught in computer science classes (I am now retired), a model is:
    1) no better than one understands the environment they are trying to model.
    2) no better than the data they have available.
    3) no better than the mathematical relations required.
    4) no better than the code that is being written (how many bugs are there that you don’t know about – How do you know when there is a bug in a model????)
    5) no better than how well truncation or roundoff is handled (after many iterations, this could become a HUGE problem).
    and 6) all of the above combined.

    I have watched predictions of an arctic summer being ice free move from 2100 to 60 years away, to 40 years away, and from the above mentioned article to 15 years away. I personally think 15 years is much closer to being reality having watched the arctic ice sheet and looked at available data over the last 7 or so years.

    Are you familiar with Dr. David Barber’s (University of Manitoba) work? If so, what is your opinion of it?

    I don’t mean to sound too critical of your work. But being I also design and develop software, I am extremely critical of my own work and I don’t release software until I am satisfied with it. My testing is to try to find the limits of my software. I learned that from working for an engineering company that had a sign above the door of the group that did Numerical Control that read something like this: “70% will pass you in school, 99.99% will fail you here”. This was back in around 1966 and I was writing NC processors that had to work with tolerances of 0.000 1 inches. There you learn about roundoff and truncation real fast!

    Anyway, keep finding those butterflies and I hope to see more papers in the near future.

    Jim Crabtree

  108. Isaac Held:


    Sorry to come to this thread so late, but I am curious about your abrupt decreases in ice. If you take the ensemble mean of all of your runs and then look at the departures from this mean, are these skewed in the sense that the negative excursions are larger than the positive ones? Or is this abruptness possibly just an impression from the superposition of a smooth ensemble mean decrease and symmetric noise?

  109. Barton Paul Levenson:

    I’ve recently run across some weird peer-reviewed stuff from a guy named Goode who is apparently working from a NASA grant — he maintains the Earth’s bolometric Bond albedo decreased measurably from 1994 to 2002, from 0.310 to 0.295 (with error bars), which if true would create a measurable climate forcing. He’s careful to note that it would take time to work its way through the climate system. Cites (and please forgive the weird characters from my cutting and pasting):

    P. R. GOODE, E. PALL_E, V. YURCHYSHYN, J. QIU, J. HICKEY, P. MONTA~N _ES RODRIGUEZ, M.-C. CHU, E. KOLBE, C.T. BROWN AND S.E. KOONIN 2002. “Sunshine, Earthshine and Climate Change: II. Solar Origins of Variations in the Earth’s ALbedo.” J. Korean Astronomical Soc. 35:1-7.

    E. Palle, P. Monta~nes Rodriguez, P.R. Goode, J. Qiu, V. Yurchyshyn, J. Hickey, M.-C. Chu, E. Kolbe, C.T. Brown, S.E. Koonin 2004. “The Earthshine Project: update on photometric and spectroscopic measurements”
    Advances in Space Research, preprint.

    Any comments?

  110. Eric Swanson:

    Re: #109

    There’s been considerable discussion in the literature about “earthshine”. A google search returned many hits, including a link to your second reference at:

    Other papers appeared in the JGR, at these links:

    There was also some discussion also in SCIENCE. Another piece in the puzzle, I’m sorry to say.

  111. Sashka:

    Looking at Fig. 2, it seems to me that (apart from one year in mid-90s) the red line representing observations sticks to the low side of the envelope generated by the ensemble of model runs. Does it not suggest a bias in the model?

  112. Cecilia Bitz:

    Re #108 Hi Isaac! No significant skewness in the A1B scenario. Another reason to dismiss the tipping point speculation. Thanks for the suggestion.

  113. Joseph O'Sullivan:

    Thanks to Dr Bitz for participating. I saw the news stories and did not have the chance to track down the original paper. It was easier just to read RC to get the full story!

    Oh, one more thing, “having a last name one letter removed from a bad beer” do you mean schlitz? I remember TV commercials for schlitz that had a taste test with bigger name beers. Schlitz lost but not by much, and they ended the commercial by saying hey we’re not that bad ;)

  114. Mark Ritzenhein:

    Re 107

    Jim Crabtree, Thank you for your short list of errors. I am glad to know that you hold yourself to a tight distrust of the natural inaccuracy of models. I, too, believe that the Arctice ice sheet will melt suddenly and rapidly.

    A general question: did climate models predict the sudden collaps of the Larsen ice shelf in the Antarctic? If not, why not? Second, does it really matter if the polar ice sheet melts in seventeen or one hundred years? This is relatively unimportant to the fact of its loss.

  115. Hank Roberts:

    For those still wondering:

  116. Nigel Williams:

    So, in relation to tipping points of knowledge, (ie we know enough to know it will happen.. etc) if we see 1 metre sea rise by 2100, that implies we see at least 12mm rise per year from now to then. So if we see 12mm per year, is that a fair enough portent that we will see 1m by 2100, and is it then fair to say that if we get 1m rise by some future date, then we will get the rest as well? It seems unlikely that sea level rise will stop until it is done, doesnt it?

    And from that, if one was working on a plan for a new (or relocated) town, how far above present day sea level would it be prudent to build that town, if it was to have a life of 500 years or so? 10m? 20m? ??

  117. llewelly:

    Nigel, I suspect the majority of buildings being built today are unlikely to remain livable for 500 years.

  118. David B. Benson:

    Nigel — Work out the sea stand rise if all of Greenland and all of West Antarctica should melt. Establish your new town some meters above that.

    While it is true that few buildings last 500 years, some do and I have certainly seen older ones than that in Europe. But the town itself has a value greater than just the structures and infrastructure in it. By all means plan ahead for being safely elevated.

  119. S. Molnar:

    Re #117: Yes, but the life of a town can reasonably be expected to exceed the life of individual structures in the town.

  120. Nigel Williams:

    Ah Llewelly, it all depends whether or not you are perched on a crag and your house is made of slate, no? :)

    Its not the buildings, its the infrastructure and land tenure that is the resource thats hard to relocate. For sure, permits for building require certainty of security of land and life of structures of 50 years. But if one is doing some long term strategic planning for an urban area, to plan for a high tide 50 years hence seems rather short sighted.

  121. David B. Benson:

    Nigel — An elevation of 30 m ought to suffice…

  122. Nigel Williams:

    Thank you gentlemen! Ah, the simple pleasures to be found in the appreciation and acceptance of a simple fact. 30m.

    The 30m contour puts my entire 150-year old city and its surrounding small towns below high tide – about 400,000 people. It also swamps most of the high quality horticultural soils, and finds us stranded on a relatively infertile plain of galcial outwash gravels, and separated from our only possible port for 150km either way along the coast too. Oh darn!

    We are in the process of preparing a new Urban Development Strategy for the city and environs to lead us sensibly through the next few hundred years. Looks like we shouldnt cling too fondly to the home we know, eh! I wonder – will our politicians heed this call? Mmmm..
    Thanks again for the info.

  123. Julian Flood:

    Re 109:

    It’s a shame we don’t have albedo measurements going back 150 years, particularly ones which distinguish between high and low level cloud. The climate effects of low level oceanic stratocumulus are huge — simple wind-powered trimarans evaporating seawater to generate hygroscopic nuclei have been proposed by Salter, Latham et al in order to buy time to correct our GW errors. A few hundred million dollars per year could offset all the calculated AGW for that year and, unlike the aerosol suggestions I’ve seen this week (was it NASA?), the trimarans can be switched off overnight if we find we have made a miscalculation.

    I’d like to see albedo measurements from the waters just off China and India. I predict a fall over the last thirty or forty years with the last ten or twenty showing a marked drop as surfactant and oil spill pollution transported down the rivers and entrained in the local surface currents suppresses the production of LL strato-cu.

    Do the models incorporate changes in the ocean surface due to pollution?


  124. David B. Benson:

    Nigel — To be precise, I have assumed 7m sea stand rise due to the melting of the entire Greenland ice sheet and 20m sea stand rise due to the melting of the entire West Antarctic ice sheet. The first number is quite solid and the second is conservatively high. If correct, this suggests the sea stand might rise as much as 27m, assuming nothing is done to amerliorate AGW.

  125. simon willace:

    Everyone seems to agree that the ice is melting at an accelerated rate. Globally all frozen water is melting which must dilute the salts in the surface body of the sea efectivly weakening surface currents.

    In the arctic the present ice cover marks the exact position where the Gulf Stream descends into the deep before it makes its way south. As this ice sheet may soon be gone, will the slower Gulf Stream just carry on over the top dissipate then disappear?

  126. Patrick Henry:

    If you want ice for the arctic, please take it from Colorado. We have had record cold and snow here.

    “Last time city was white for so long? 1914
    Long, cold spell dredges up images of long gone storms

    If last month felt like the coldest in more than 16 years in Fort Collins, that’s because it was.

    January 2007 was the sixth-coldest in the past 50 years. It averaged 23.7 degrees last month, more than 14 degrees colder than 12 months earlier and 5 degrees colder than usual.

    And that 11-inch blanket of snow covering much of the city is probably unmatched since the winter of 1913-14, said State Climatologist Nolan Doesken. “

  127. Steven Soleri:


    Cecilia, you do not have to go to ice field data collection to determine there have been recent and rapid deterioration of ice fields and glaciers in the artic. Read the letters of gold rush miners thankful that the temperatures have warmed over what the native peoples recalled just 20 year prior. Another warming period is well reported by locals in the 30′s. And you want to run an alarm on your data. A researcher that overlooks the obvious–there are first hand accounts now available of changing artic temperatures. Cecilia reports that we can turn back the CO2 clock and save the earth??? If CO2 is the problem then the Chinese and India have our perverbial behind in a vice. And I can guarantee you they have no interest in a CO2 or feedback hypothesis.