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Arctic Sea Ice decline in the 21st Century

Filed under: — group @ 12 January 2007 - (Français)

Guest Commentary by Cecilia Bitz, University of Washington

Last month a paper I co-authored received considerable media attention. Headlines read “Experts warn North Pole will be ‘ice free’ by 2040″, “The Big Melt: Loss of Sea Ice Snowballs“, and “Arctic Clear for Summer Sailing by 2040: Models Predict Rapid Decline of Sea Ice”. The story also reached NPR, BBC, CBC, the Discovery channel, and Fox News, among others. Dr. Marika Holland, the first author of the paper, was inundated with media attention. About a dozen journalists contacted me too. I was impressed by the questions they posed — questions that probably reflect what the public most wants to know. However, after giving lengthy interviews, I would read the resulting article and see my explanations boiled down to a few lines. In this essay, I’d like to explain the science in the paper and give my answers to the most often asked questions.

In our paper (with co-author Bruno Tremblay), we examined the September Arctic sea ice cover in the 20th and 21st centuries in climate models, and found occasional decades of very rapid retreat. The most extreme case was a decrease from 6 to 2 million square kilometers in a decade (see Fig 1). This is about 4 times faster than the decline that has been observed in the past decade.


Figure 1: (a) Northern Hemisphere sea ice extent in September from one integration of the Community Climate System Model version 3 (CCSM3) with observations from the satellite era shown in red. The light blue line is a 5-yr running mean. The three lower panels show the September ice concentration (ice floes are separated by open water) in three select decades.

It is common practice to run climate models multiple times with slight variations to the initial conditions. Because the system is chaotic, the natural variability in each run is random and uncorrelated from one run to the next. When an ensemble of runs is averaged, the natural variability is reduced in the ensemble mean, and it is easier to detect a significant trend.

An ensemble of runs offers an opportunity to evaluate rare events too, such as extreme sea ice decay. We were in search of evidence for “tipping points“, which several authors have speculated might exist in sea ice. RealClimate places sea ice in the category of systems with “known unknowns” with regard to tipping points. This means we know there are thresholds involving sea ice (e.g., it can cease to exist), but we don’t know when, or if, the climate will arrive at one.

Only one of seven ensemble members had an event as extreme as quoted above, and it resulted in near ice-free conditions for September by 2040 (see Fig 1d). (The sea ice grows back at least for some portion of winter for the duration of the 21st century.) However, every ensemble member had an event 5 years or longer at some time in the 21st century when the sea ice retreat was about 3 times faster than the observed retreat since 2001 (see Fig 2). These ensemble members took about 5–10 years longer to become nearly ice-free in September than the most extreme case.

As illustrated in Fig 1, the sea ice retreat accelerates during the 21st century as the ice decays and more sunlight is absorbed by the ocean (the positive ice-albedo feedback). Increasing ocean heat transport under the sea ice adds to the melt back. The retreat appears abrupt when natural variability in the ocean heat transport into the Arctic Ocean is anomalously high. We did not find clear evidence of a threshold, which can be difficult to identify given the variability and complexity of the climate system. Therefore we can neither verify or rule-out the existence of a tipping point. Regardless, the rapid declines seen in our runs are a serious concern.


Figure 2: Northern Hemisphere sea ice extent in September for all seven integration of the CCSM3 with observations from satellite era shown in black.

Most common questions asked by journalists

1) How does our model compare with the trend in the observed record?

The trends in the seven ensemble members for 1979-2006 span the trend in the observations: Some members retreat a little faster and some a little slower, as expected from the random natural variability in the runs (see Fig 2). The model also reproduces the mean and variance of the observations with good fidelity.

2) Other scientists are predicting an ice-free Arctic in September by the year 2060-2080, why is this model predicting it 20-40 years sooner?

First consider estimates based on extrapolation from the observational record. I’ve heard these numbers quoted in the media, but I have not seen a reference to a scientific paper that discusses the analysis in any detail. Figures 2 and 3 illustrate the danger of making an estimate of the future from the observational period. The future trend is not linear, the observational record is too short and the ice-free time is too far in the future to trust extrapolation. If one carries out such an exercise anyway, extrapolation from a linear fit to 1979–2006 gives a zero intersect (indicating the first ice-free year in the future) at about 2110 (see Fig 3). If instead one uses just the last decade, the extrapolation gives 2060. Both estimates are questionable, and so instead we turn to climate models.


Figure 3: Extrapolating into the future from the observational record.

3) Is sea ice in our model retreating faster than in other models?

Figure 4 shows September ice retreat in 16 models that were archived for the IPCC AR4. The most extreme predictions are from models that have too much or too little sea ice extent compared to observations, so it is important for a model to produce the correct sea ice coverage in the past. Some of the spread is expected from natural variability, but much depends on differing model sensitivity relating to the representation of sea ice, heat transport by the ocean, and cloud cover. It is not possible to identify the most accurate model prediction, although I think it is safe to rule out some of the outliers owing to their poor match to the observations.

About half of the models become ice-free in September during the 21st century. I included one ensemble member from our model, CCSM3, which is in the middle of the pack until about 2020. Our model run retreats faster than most after about 2020, but it isn’t radically different.

There is considerable uncertainty in future model projections, and Figs 2 and 4 illustrate why it would be better not to focus too much on the year 2040, which to our dismay was highly publicized. The more important message from models is that all but a few outliers predict enourmous sea ice retreat this century. At least a few respectable models predict a nearly ice-free Arctic by midcentury, with a retreat that may be punctuated by rapid events.


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.


127 Responses to “Arctic Sea Ice decline in the 21st Century”

  1. 51
    Edward Greisch says:

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

  2. 52
    Dmitry Vyushin says:

    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 ?

  3. 53
    Timothy says:

    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.

  4. 54
    Victor Amoroso says:

    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.

  5. 55

    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.

  6. 56
    Neil Thomas says:

    Shrinking the forecast window

    Hi

    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?

  7. 57
    Leonard Evens says:

    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.

  8. 58
    pete best says:

    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.

  9. 59
    Ron Taylor says:

    Re 53

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

  10. 60
    Judith Curry says:

    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

  11. 61

    Judith,

    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 http://polar.ncep.noaa.gov/seaice/analysis/nh/nh.20061010.gif See http://polar.ncep.noaa.gov/seaice/nh.html for the key to the colours.

  12. 62
    Nigel Williams says:

    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.

  13. 63
    Mark Hadfield says:

    “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?

  14. 64
    Aaron Lewis says:

    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.

    Aaron

  15. 65

    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.

  16. 66
    Pekka Kostamo says:

    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.

  17. 67
    llewelly says:

    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.

  18. 68
    Steve Bloom says:

    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.

  19. 69
    Ike Solem says:

    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 http://www.gsfc.nasa.gov/topstory/20020606greenland.html 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.

  20. 70
    NIKOS ADAMOPOULOS says:

    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]

  21. 71
    Neil Thomas says:

    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.

  22. 72
    Matt says:

    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 :)

  23. 73
    pete best says:

    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.

  24. 74
    pete best says:

    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.

    http://alum.mit.edu/docs/ne/alc/2006presentations/plenary_energyresearch.pdf

    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.

  25. 75
    Eli Rabett says:

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

  26. 76
    pete best says:

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

  27. 77
    John L. McCormick says:

    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.

  28. 78
    Ike Solem says:

    RE#72,
    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.

    Re#74,
    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.

  29. 79
    yartrebo says:

    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?

  30. 80
    yartrebo says:

    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.

  31. 81
    John L. McCormick says:

    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.

  32. 82
    Louise says:

    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?

  33. 83
    pete best says:

    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.

  34. 84
    Charles Muller says:

    #55
    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.

    Ref.
    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.

  35. 85
    Dan says:

    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.

  36. 86
    Richard Ordway says:

    Re. comment 50.

    William,

    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…

  37. 87
    Lynn Vincentnathan says:

    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).

  38. 88
    Ark says:

    #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).

  39. 89
    Ike Solem says:

    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.

  40. 90
    matt says:

    #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.

  41. 91
    pete best says:

    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.

  42. 92
    Deepak Rughani says:

    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…

  43. 93
    Alan says:

    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.

  44. 94
    pete best says:

    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

  45. 95
    Nick Gotts says:

    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?

  46. 96
    John L. McCormick says:

    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.

  47. 97

    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.

  48. 98
    Hank Roberts says:

    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]
    http://www.bepress.com/cgi/viewcontent.cgi?article=1229&context=ev

    Letter: Pay-As-You-Drive Is More Apt to Reduce Accidents … insurance market. If drivers faced economic …
    http://www.bepress.com/cgi/viewcontent.cgi?article=1232&context=ev

  49. 99
    Steve Sadlov says:

    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.

  50. 100

    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?
    See: http://www.sciencemag.org/cgi/content/abstract/299/5613/1725


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