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Sea ice minimum forecasts

Filed under: — gavin @ 17 July 2009

One of the interesting things about being a scientist is seeing how unexpected observations can galvanize the community into looking at a problem in a different way than before. A good example of this is the unexpectedly low Arctic sea ice minimum in 2007 and the near-repeat in 2008. What was unexpected was not the long term decline of summer ice (this has long been a robust prediction), but the size of 2007 and 2008 decreases which were much larger than any model had hinted at. This model-data mismatch raises a number of obvious questions – were the data reliable? are the models missing some key physics? is the comparison being done appropriately? – and some less obvious ones – to what extent is the summer sea ice minimum even predictable? what is the role of pre-conditioning from the previous year vs. the stochastic nature of the weather patterns in any particular summer?

The concentration of polar expertise on the last couple of questions has increased enormously in the last couple of years, and the summer minimum of 2009 will be a good test of some of the ideas that are being discussed. The point is that whether 2009 is or is not a record-setting or near-record setting minimum, the science behind what happens is going to be a lot more interesting than the September headline.

In the wake of the 2007 minimum, a lot of energy went in to discussing what this meant for 2008. Had the Arctic moved into a different regime where such minima would become normal or was this an outlier caused by exceptional weather patterns? Actually this is a bit of false dichotomy since they aren’t exclusive. Exceptional patterns of winds are always going to be the proximate cause of any extreme ice extent, but the regime provides a background upon which those patterns act. For instance, in the paper by Nghiem et al, they showed the influence of wind patterns in moving a lot of thick ice out of the Arctic in early 2007, but also showed that similar patterns had not had the same impact in other years with higher background amounts of ice.

This ‘background’ influence implies that there might indeed be the possibility of forecasting the sea ice minimum a few months ahead of time. And anytime there is the potential to make and test predictions in seasonal forecasting, scientists usually jump at the chance. So it proved for 2008.

Some forecasting efforts were organised through the SEARCH group of polar researchers, and I am aware of at least two informal betting pools that were set up. Another group of forecasts can be found from the Arctic ice forecasting center at the University of Colorado. I personally don’t think that the intrinsic worth of a successful prediction of overall sea ice extent or area is that societally relevant – interest in open shipping lanes that might be commercially important need much more fine-grained information for instance – but I think the predictions are interesting for improving understanding of Arctic processes themselves (and hopefully that improved understanding will eventually feed into the models and provide better tests and targets for their simulations).

What was particularly interesting about last years forecasts was the vast range of forecasting strategies. Some were just expert guestimates, some people used linear regression on past data, some were simply based on persistence, or persistence of the trend. In more mature forecasting endeavours, the methods tend to be more clustered around one or two proven strategies, but in this case the background work is still underway.

Estimates made in June 2008 for the September minimum extent showed a wide range – from around 2.9 to 5.6 M km2. One of the lowest estimates assumed that the key criteria was the survivability of first year ice. If one took that to be a fixed percentage based on past behaviour, then because there was so much first year ice around in early 2008, the minimum would be very low (see also Drobot et al, 2008). This turned out not to be a great approach – much more first year ice survived than was predicted by this method. The key difference was the much greater amount of first year ice there was near the pole. Some of the higher values assumed a simple reversion to trend (i.e. extrapolation forward from the long-term trend to 2008).

Only a couple of the forecasts used physics-based models to make the prediction (for instance, Zhang et al, 2008). This is somewhat surprising until one realises how much work is needed to do this properly. You need real time data to initialise the models, you need to do multiple realisations to average over any sensitivity to the weather, and even then you might not get a range of values that was tight enough to provide useful information.

So how did people do? The actual 2008 September minimum was 4.7 M km2, which was close to the median of the June forecasts (4.4 M km2) – and remember that the 2007 minimum was 4.3 M km2. However, the spread was quite wide. The best estimates used both numerical models and statistical predictors (for instance the amount of ice thicker than 1m). But have these approaches matured this time around?

In this year’s June outlook, there is significantly more clustering around the median, and a smaller spread (3.2 to 5.0 M km2) than last year. As with last year, the lowest forecast is based on a low survivability criteria for first year ice and I expect that this (as with last year) will not pan out – things have changed too much for previous decades’ statistical fits on this metric to be applicable. However, the group with the low forecast have put in a ‘less aggressive’ forecast (4.7 M km2) which is right at the median. That would be equal to last year’s minimum, but not a new record. It would still be well below the sea ice trend expected by the IPCC AR4 models (Stroeve et al, 2008).

There is an obvious excitement related to how this will pan out, but it’s important that the thrill of getting a prediction right doesn’t translate into actually wanting the situation to get worse. Arctic ice cover is not just a number, but rather a metric of a profound and disruptive change in an important ecosystem and element of the climate. While it doesn’t look at all likely, the best outcome would be for all the estimates to be too low.


858 Responses to “Sea ice minimum forecasts”

  1. 101
    J. Bob says:

    One can look at a graph in many ways. If you look at the same season anomaly end points, nothing much has happened. From 1979 to 2001 it was basically flat. If you look at the anomaly from 2001-2007, it trends down. If you look at the anomaly from beginning of 2008-now, it trending up. Unfortunately we do not have enough history to say if this is normal or something else. And if it’s something else, what is it? Remember, I said “about normal”, with nothing really standing out to indicate a strong bias one way or another.

    So Michael Sweet, where do you want to draw the line?

  2. 102
    Jacob Mack says:

    My only concern is, I have not seen Ray Ladbury much as of late; he was a prolofic poster of great merit as well.

  3. 103
    J. Bob says:

    In all the differences of opinion here, does anyone have a handle of just how accurate the data we are discussing is?
    0.1%, 1% 10%?

  4. 104
    Mike Hilson says:

    Anyone have a response to my post #34 ?

  5. 105

    Steve L writes:

    The link in comment 70 is to a Time magazine piece that implies an orbiting moon can warm a planet over geological time.

    Either you misinterpreted the article or someone at Time doesn’t know what they’re talking about. I can’t think of any way the Moon could significantly affect the Earth’s climate, other than crashing into it.

  6. 106

    The inaptly named “truth” writes:

    Why is the AGW side so desperate to have all the focus on CO2?

    http://BartonPaulLevenson.com/Correlation.html

  7. 107
    Pekka Kostamo says:

    A favourite site:
    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/sea.ice.anomaly.timeseries.jpg

    On this graph one easily sees both the slow trend down (3,5%/dec) as well as the short term variability due to “the weather”.

    One also sees that there is something of a mode change since 2007. If this character change is transitional or permanent remains to be seen, but three seasons in a row makes one think.

    The mode change became possible with continued thinning of the ice. Thin ice is more susceptible to weather, particularly to the windws. So the 2007 persistent winds were able to drive lots of ice out to the Atlantic and also pile some against the Greenland coast. Sensitivity to high solar input is also increased.

    As to the discussion about global ice cover, one needs to keep in mind that the Arctic sea ice can not grow in a linear manner. After the ocean is frozen over coast-to-coast, area growth can only happen in two narrow sectors. Besides, sea currents limit ice expansion in both hemispheres, not just the surface air temperatures as apparently assumed by many writers.

    Predicting sea ice developments is probably as difficult as of any other regional change brought about by the global warming. Regional changes are of utmost importance for practical reasons, and will no doubt remain the focus of research.

  8. 108

    Thanks for a clear comment, Pekka.

    This image has been the source of some comment here of late. Some (J. Bob) see it as “flat” or maybe “sort of” flat. I see that the first dozen years are largely above the mean, with occasional excursions below it, while the last dozen years have the opposite pattern. That would be the -3.5% trend you mention, of course.

    Mike, 34 & 104, I’m no expert, but I doubt that ice thickness has a measurable impact on ice mobility. Seems to me the only strong effect would be when ice is grounded in shallow water, and given that maximum thickness is only a matter of tens of meters at most, this scenario will not be relevant for the vast preponderance of Arctic waters. My two cents.

  9. 109
    Hank Roberts says:

    Steve L — 18 Jul 2009 @ 2:54 pm
    is pointing to an article about Saturn’s moons.

    Steve, look into it a bit more. Once you understand what they’re describing there, you can compare the situation of other pairs and have an idea how much effect gravitational flexing will have. This may help
    http://www.nature.com/ngeo/journal/v2/n1/abs/ngeo396.html

    Compare say Sun/Mercury, and Earth/Luna — look at the relative size, distance, and particularly the materials involved, very different in each case. Your question’s addressed, you’ll find it if you dig for it with Google Scholar, or any good reference librarian can help you.

  10. 110
    Hank Roberts says:

    J.Bob, yes, one can look at a graph in many ways. You can look at it like a hazy distant mountain range, or a washboard, or a ski jump, or anything you imagine.

    Once you take Statistics 101, you lose that ability and find yourself looking at it in only a few ways, the ones that have some use in understanding what it represents.

  11. 111
    Stephen says:

    Per post 88, Wayne Davidson:

    “…there is a significant meltdown, by Northern Hemisphere multi year ice on the verge of extinction….”

    Can we agree that using the word “extinction” is a bit hyperbolic? I know it’s found its way into the GW discussion per Al Gore and others, but doesn’t it strike you as silly, and unproductive to your argument?

    Let’s leave “extinction” where it properly belongs, in the world of animals and plants and genetic code.

  12. 112
    Kea Duckenfield says:

    Did I miss it? Was there no discussion here of the 699 images released by USGS last Wednesday, 1-m nominal spatial resolution, spanning the last 10 years and covering several different sites in the Arctic including Barrow?

    I thought this dataset would be causing excitement among those interested in modeling sea ice decline in the Arctic. Am I wrong, or did the word not get out?

    See: http://gfl.usgs.gov/ArcticSeaIce.shtml; http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=12631

    Would love to read realclimate’s opinions on how/how much this data might contribute to model projections.

  13. 113
    Steve L says:

    BPL @106 — maybe a bit of both; why not read the short Time article and find out? [I'm not selling subscriptions to Time, don't worry.] This is how I interpret it: a moon of Saturn has liquid water because its own satellites cause it to flex and the friction keeps it warm. So I figure the Moon’s kinetic energy is transmitted to some degree to the Earth by gravity in the form of tidal forces that warm the Earth via friction.
    Thomas @81 gets what I mean — the Moon is getting farther from the Earth, so these tidal forces are diminishing, perhaps cooling the Earth compared to its early history when the Sun was fainter. Your use of the term “significantly” has the usual problems, and I don’t know if this effect would match your criteria.

  14. 114
    Mark says:

    “Why is the AGW side so desperate to have all the focus on CO2?”

    Because when you’re bleeding out your arm where you hand used to be, they put a tourniquet around that rather than see to the bloody nose. Even though it’s leaking blood too.

  15. 115
    Mark says:

    “how accurate the data we are discussing is?

    Comment by J. Bob ”

    What is “the data” you ask for.

    After all, the length of a day is quite accurately known. The speed of the laden swallow is less accurately known.

    Both are data.

    Remember: some data is more accurately known than others.
    Remember: accuracy doesn’t mean reliability. You can accurately measure maximum temperatures at LHR on one day. But the expected value the next day has a range around that value based not on accuracy but on reliability.

  16. 116
    Mark says:

    “So Michael Sweet, where do you want to draw the line?

    Comment by J. Bob ”

    As in anything to do with putting an equation to real life, when the error of estimation is low.

    If your error in estimating a trend has an error less than 0.05C per decade, you have an accuracy of estimation of 0.05C per decade. If you have a graph fitted line of 0.0C/decade you can then call it flat.

    If your error is bigger than 0.2C per decade, a fitted line of 0.0C per decade cannot be called flat, since the long term trend of 0.2C/decade still is comfortably within the error of your estimation of the trend.

    VERY basic stats.

  17. 117
    Mark says:

    “the Moon is getting farther from the Earth, so these tidal forces are diminishing, perhaps cooling the Earth compared to its early history when the Sun was fainter.
    Comment by Steve L”

    So do the maths.

    Even if you assume 100% of the tidal forces cause warmth in the earth, I don’t think even 10 million years is going to make much difference.

    But work it out. Even over-estimate it. Then convert that energy into watts per square metre.

    If over 10 million years, that comes to less than 0.01W/m^2 it can be ignored. It it gets over ~0.1W/m^2 it may have something to say over the paleo record (about as much as sunspot activity, for example).

  18. 118
    Mark says:

    “Let’s leave “extinction” where it properly belongs, in the world of animals and plants and genetic code.

    Comment by Stephen”

    ex·tinct (k-stngkt)
    adj.
    1. No longer existing or living: an extinct species.
    2. No longer burning or active: an extinct volcano.
    3. No longer in use: an extinct custom. See Synonyms at dead.
    4. Law Lacking a claimant; void: an extinct title.

    Source: WordNet (r) 1.7

    extinct
    adj 1: no longer in existence; lost or especially having died out
    leaving no living representatives; “an extinct species
    of fish”; “an extinct royal family”; “extinct laws and
    customs” [syn: nonextant] [ant: extant]
    2: of e.g. volcanos; permanently inactive; “an extinct volcano”
    [syn: inactive] [ant: active, dormant]
    3: of a fire; being out or having grown cold; “threw his
    extinct cigarette into the stream”; “faint smoke from the
    extinguished candle”; “the fire is out”; “the quenched
    flames” [syn: extinguished, out, quenched]

  19. 119
    Nick O. says:

    Re. the goo appearing in Arctic waters (e.g. # 42 – cougar_w), I wonder if this is something to do with buried submarine ice starting to melt, caused by warming of waters above it?

    There are miles of this stuff down there, many tens of metres thick in places, buried under rafts of old Pleistocene sediments, some of the latter well mixed up with old tundra and bog deposits. A lot of it, clearly, is near the present shoreline, where water is not too deep, say less than a couple of hundred metres. Much of this has been melting slowly, we think, since the end of the Pleistocene, but there’s no reason why the rate of melt can’t speed up. It could also explain some of the non-linearity of the ice-melt response e.g. much of the phase change taking place in the surface (floating) ice, this then clears the way for sunlight to penetrate deeper, and the phase change then switches a bit to the buried ice. Quite complex and difficult, but could be just another part of the story, a filament rather than a big effect. If anyone wants to follow this up, I’ll try to dig out a few references.

  20. 120
    Hank Roberts says:

    > Arctic Goo
    http://scienceblogs.com/guiltyplanet/2009/07/arctic_goo_update.php
    Category: What the…?
    Posted on: July 19, 2009 2:19 PM, by Jennifer L. Jacquet
    “It was marine algae.”

  21. 121

    Steve L., consider some of the numbers involved.

    Mass of Enceladus:
    (1.080 22 ± 0.001 01) × 10(20th) kg (1.8×10-5 Earths)
    Mass of Saturn: 5.6846 × 10(26th) kg (95.152 Earths)

    Orbital axis of Enceladus: 237,948 km

    Mass of Luna: 7.347 7 × 10(22nd) kg (0.0123 Earths)
    Mass of Earth: 5.9736 × 10(24th) kg

    Orbital axis of Luna: 384,399 km

    First, obviously, is the fact that Enceladus is five whole orders of magnitude smaller than Earth, which right there would make the heating effect 10,000 times smaller, all other things being equal.

    Then you have the fact that Saturn is four orders of magnitude bigger than the moon, which means a further reduction in heating of about 1,000. That gets us to a heating effect that’s about one ten-millionth.

    From here on, things get a bit picayune by comparison, but there’s the fact that the orbital radius is about 50% greater for the Earth/Luna pair; that gives a reduction of about one-fourth. (Tidal force is inversely proportional to the cube of the distance.)

    You do have to give back a factor of about 250, because tidal force is also proportional to the radius of the body affected, and Earth’s diameter is about 250 times that of Enceladus.

    That ends us up where? An effect that’s 63 ten-millionths?

    And of course all of this ignores what your source posited as the main source of Enceladus’s heating: the other moons which pass it closely–Earth has nothing like that. I don’t know how to quantify that, but whatever it is, it’s taking away from the effect you propose–and your source, again, seemed to say that it was very significant. So I think you can kiss this idea’s viability goodbye.

    As to the idea that lunar retreat can affect the “short term things like sea ice” with orbital retreat of a few cm per year is just not workable. Measurable effects over many millions of years, OK. Over a decade, or two, or ten, NOT.

  22. 122

    Oops, I slipped a couple of decimal points, didn’t I? I really miss the preview function. . .

    Well, correcting it should make the overall argument stronger. 100 times stronger, in fact, unless I’m screwing up the math again.

    Did I mention that I’m an artsie?

  23. 123

    I updated the Monckton page to include perspective on the notion of there is no problem with regard to global sea ice extent (scroll down to global sea ice extent).

    http://www.ossfoundation.us/projects/environment/global-warming/myths/christopher-monckton

    Although redundant, as always, please note that sea ice extent is only part of the signal and ice mass loss is a more obvious indicator in this case.

    This is not to say sea ice extent has no importance, merely that context is needed when discussing these issues.

  24. 124
    Doug Bostrom says:

    Jacob Mack 19 Jul 2009 at 10:31 pm

    “My only concern is, I have not seen Ray Ladbury much as of late; he was a prolific poster of great merit as well.”

    Absent by doctor’s orders, suffering from “climate elbow”?

    CE is similar to tennis elbow but also may involve carpal tunnel syndrome as a secondary pathology. CE is caused and aggravated by endlessly swatting down wads of revanchist anti-science, anti-progress propaganda on a playing court of shape and dimensions boundlessly elastic depending on the rhetorically expedient needs of the particular Pangloss team member playing in opposition.

  25. 125
    wili says:

    Good points, Nick O.

    Aren’t there a lot of areas on the continental shelf where the depth of the water is more like tens of meters than hundreds of meters?

    At what depth could surface warming affect ice on the sea floor?

    Same for sunlight. How deep till sunlight penetration becomes insignificant (or how shallow till it can becomes significant)?

  26. 126
    dhogaza says:

    Absent by doctor’s orders, suffering from “climate elbow”?

    Or “climate forehead”, from repeated attempts to butt through the brick wall of denialism…

    It’s summer. Hopefully he’s out exploring the radiation hardness of various sunblock lotions at some place far, far from work and the internet …

  27. 127

    Re #106 by Barton- Interesting and informative link. Thank you. I notice,at first glance, that there hasn’t been a negative anomaly since 1977!The accompanying graph, t-statistics and correlation coefficient should be sufficient to convince even hard line deniers of the relationship between CO2 and increasing temps,but the die hards are out there as shown by Barton’s note at the end.

  28. 128
    Steve L says:

    Responding to Mark @117 and to Kevin @121… Thomas’s response in 81 gave me some terms to help me google (http://earthobservatory.nasa.gov/IOTD/view.php?id=654). [Nice to know that I've now caught up to what scientists were wondering about this 200 years ago.] The current effect is estimated at 4 terawatts (about a quarter of it exerted in the deep ocean). The surface area of Earth is 510,000,000 sq.km. If I’m converting correctly, that gives me 0.01 W/m^2. Is that correct? If it is, then it almost satisfies Mark, and then the next important part is figuring out how much that has changed since the sun was young and faint (a couple of billion years ago).

    I could try to extrapolate the 3.8 cm/yr backward in time to see how much greater the tidal forces would be, but that assumes a constant rate of orbital increase (bad assumption — orbital increase is thought to have slowed a lot), and it assumes constant month length (bad assumption — it’s thought to have completed closer orbits more frequently). But if I do the extrapolation and then use the square of the distance to compare to present (I’m just a fish biologist, I have no idea…) then I get a 20% reduction in heating since nearly a billion years ago.

    But I think maybe a better way to do this is to assume that all of the slowing of Earth’s rotation around its own axis is due to friction of the sloshing tide (?), and then figure out how much friction is required to slow the Earth from one rotation every 18 hours (why I extrapolated to nearly a billion yrs ago above) to a day length of 24 hours now. Can we do that? I don’t know how (and I don’t know if we need to account for the molten interior — hard boiled egg keeps spinning, a raw one slows down quickly).

    I think this latter approach is preferable, but of course I’m ignoring that the Sun’s gravity also plays a role in tides. But at least we get a tidy maximum effect. (Right?) With regard to short term things like one year’s sea ice minimum, Kevin, which is more akin to weather than climate, I think it’s MORE likely that tides can have an important effect — since the long term effects tend to balance out. Wind-driven currents are blamed for a lot of what happened to produce the 2007 minimum. A well-timed spring tide (when the Moon and Sun are both pulling in the same direction) might also result in strong currents that have an impact. Do the maths? Hopefully Mark (or somebody) will give me more hints on how to do so.

  29. 129
    Mark says:

    “At what depth could surface warming affect ice on the sea floor?”

    Well the thermocline is usually some 100′s of feet below the surface.

    If the sea floor is below that, it won’t.

    You then have to rely in mixing and inversion layers turning over.

    Sunlight doesn’t extend much below 100m anywhere and blue light goes furthest. IR much, much less.

  30. 130
    Mark says:

    ” Do the maths? Hopefully Mark (or somebody) will give me more hints on how to do so.

    Comment by Steve L ”

    Mass of water “lifted” by the moon.

    Revolves once every day.

    1/2mv^2

    Then do it with the moon as much further away as it will be in 100 years, 1 million years and 10 million years.

    Check the differences.

    I DO hope you aren’t employed in a scientific capacity.

    To a large extent, I hope it’s not engineering either.

    These are standard “back of the envelope” ideas that should, if you are any good at those professions, be practically second nature.

  31. 131
    Mark says:

    “But I think maybe a better way to do this is to assume that all of the slowing of Earth’s rotation around its own axis is due to friction of the sloshing tide (?)”

    No, that would be exceedingly wrong.

    At least it isn’t wrong for most people, but someone who knows that the earth is slowing its rotation AND that the moon is getting further away should have known what the heck is going on.

    Our rotational energy is going in to throwing the moon away. A little like the slingshot effect is taking rotational energy from the body it is using for the slingshot to give it more kinetic energy on leaving its influence.

  32. 132
    Mark says:

    Steve, taking the 0.01W/m^2 and saying it was 20% different means that over the 1 billion years, the change has been 0.005W/m^2.

    In 100 years, this would be…?

    1/2,000,000 W/m^2.

    I wouldn’t like to say we get more effect from Idi Amin having walked a mile once, but that is a REALLY small number.

  33. 133
    HenkL says:

    re Mike Hilson (#34/#104):

    There is a natural flow from the Bering Strait towards the Fram Strait. The latest (east of NE-Greenland) is the largest area for Arctic ice flowing to the south. A minor one is the (narrow) Nansen Strait between N-Greenland and the Canadian Ellesmere Island. Ice usually doesn’t flow south in the Bering Strait.

    Arctic sea ice is moving always, even in wintertime. The speed and direction of movement depends on the flow of the water beneath the ice and on the winds at the surface.

    The speed at which broken parts of ice can flow southwards also depends on the width of the Strait it is flowing through. The Fram Strait has enough width to let even the biggest sheets of ice pass.
    But the Nansen Strait is only 40 km width. It was ice free 10 days ago, when the southern part of the Lincoln Sea to the north was beginning to fall apart. But today, after the ice sheets of the Lincoln Sea have disintegrated into smaller parts, there is a kind of traffic jam in the northern part of the Nansen Strait.

    But I think the flowing of Arctic ice parts southwards is a rather minor component in the process of ice loss. More important are ‘in situ’ processes like insolation (no clouds) and warmer air spreading from the continents over ice areas.

  34. 134
    geo says:

    I have to agree it will be very exciting to see how this works out.

    And even more than “1st year ice”, how the second year ice (the difference between 2007 and 2008 minimums) does. Will it perform closer to 1st year ice, closer to mature ice, or somewhere in between?

    Looking at 2005 vs 2008, it is easy to see that 2008 was on the same curve until mid-August, when “1st year ice-itis” hit and it plunged.

    Doncha just love new data?

  35. 135
    geo says:

    Shall we start a pool for 2009 arctic summer minimum? I call 5.1M km2.

  36. 136
    Steve L says:

    Mark @130, why question my scientific bonafides? (In fact, I’m an employed scientist studying fish genetics, but why that matters in a blog for sharing scientific information, I don’t know.) And why the heck are you talking about 100 years and 10 million years? I’m talking about billions of years — the faint young Sun problem is evidence of liquid water on Earth eg 3 bya (http://en.wikipedia.org/wiki/Faint_young_Sun_paradox).

    Mark @132, again there’s the problem of 100 years… Anyway, my attempt at figuring the difference between now and a billion years ago may have some over-estimation, but the fact that the Moon was a lot closer billions of years ago (I chose 1 billion because that’s the most ancient information I came across on day length, but 3 bya would have been more relevant), and apparently orbited the Earth a lot faster back then means that the change from .01 to .008 W/m2 is a bad underestimate.

    Mark @131, I’ll have to think about this more. Earth’s spin is throwing the Moon away. Okay…. Little is obvious to me, including this: how does that slow the Earth’s spin? The Moon creates tides and the friction slows the Earth, non? I can tell this is going to be the kind of thing that helped me choose biology rather than physics, but I don’t see why my weaknesses in this kind of thinking relative to climate scientists and physicists should invite ridicule. Indeed, this blog is valuable specifically because people like me are far behind many contributors here who like to try and help us catch up a bit in understanding the world.

  37. 137
    Steve L says:

    I guess I made a mistake in trying to put two things about the Moon together, really to make one argument. The main argument I meant to make was that tides could have an impact on a given year’s Arctic sea ice minimum. A spring tide when ice was vulnerable could create currents that break more ice, that pile up more ice into a compact area or export more ice, that affect salinities and help melt more ice, etc, than a neap tide in a year with otherwise identical conditions might. How much more? I dunno. I’d like to. Or I’d like to compare wind energy at sea ice level to tidal current energy at sea ice level.

    I thought it might help people to accept the Moon as being worth investigating if I posted something obout another way the Moon might be important for things that interest people at this blog. I regret using that approach. This second lunar effect would operate on a much, much longer time scale than the main point, which is unrelated other than the fact that the Moon is involved. I’m still interested in whether the Moon has something to say about the young Sun paradox, and I’m thankful to any who help me work it out (or point me to a good source). But by introducing both topics, I seem to have got people thinking that I believe changes to the Moon’s orbit has a considerable impact in the short term. That is certainly not what I have been arguing, or at least it’s not what I have tried to argue.

  38. 138
    truth says:

    Gavin [ re 69 response]
    Even though you’ve co-authored papers with Drew Shindell, it doesn’t alter the fact that he said the following: he said the following “We will have very little leverage over climate in the next couple of decades if we’re just looking at carbon dioxide,” Shindell said. “If we want to try to stop the Arctic summer sea ice from melting completely over the next few decades, we’re much better off looking at aerosols and ozone.”
    Does Drew Shindell not really mean that last clause—‘we’re much better off looking at aerosols and ozone’?
    I realize he had a guest post at Real Climate, but the political leaders of the world are only talking about CO2, and trading schemes—–never about black carbon.
    They take their cues from the AGW scientists, and are taking no cues about black carbon.
    Our former Prime Minister established a Global Forest Initiative with initial funding of $200million , in 2006/07, to be used to try to stop the forest burning around the world, that’s the largest contributor to the black carbon problem.
    He was just sneered at and vilified by Greens and other AGW proponents for that policy, and lost office largely on the AGW issue—at a time when the AGW scientists knew about the impact of black carbon in the Arctic.
    Will there be as much or more focus on aerosols and ozone at the Copenhagen conference, as on CO2 and emissions trading and carbon taxes?

    [Response: You are creating a false dichotomy - the fact that tackling black carbon and methane and other ozone precursors would be useful does not imply that CO2 can be ignored. Drew, myself and even Jim Hansen have made this point repeatedly. - gavin]

  39. 139
    J. Bob says:

    #115,#116 – Mark, let me spell it out more, so you can understand. The data I am referring to is the plot of global sea ice from:

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg

    namely how accurate is the data plotted therein. Is the north and south polar ice data accurate to what tolerance? Remember you have uncertainties in the orbital trajectory, the vehicle attitude, pointing of the antenna, beam errors, after that the signal is quantized (another error/uncertainty), and transmitted back to earth. In addition you have long term aging of the components, equipment temperature gradients, radiation effects, etc. All of these effect the accuracy of the data.
    So what is the orbit to orbit, day to day, year to year, decade to decade 1 sigma error/uncertainty?
    0.01, 0.1, 1.0, 10 mill. sq. km.?

    Seems that before one can use statistics, effectively, one has to have an idea of the quality of the data. Statistics will not improve the smell of garbage coming in to garbage going out.

  40. 140
    BobFJ says:

    ALL: Here is an interesting new paper published in GRL on 16/July/09

    Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation
    http://www.agu.org/pubs/crossref/2009/2009GL038777.shtml

    Abstract:
    Understanding Arctic temperature variability is essential for assessing possible future melting of the Greenland ice sheet, Arctic sea ice and Arctic permafrost. Temperature trend reversals in 1940 and 1970 separate two Arctic warming periods (1910–1940 and 1970–2008) by a significant 1940–1970 cooling period. Analyzing temperature records of the Arctic meteorological stations we find that (a) the Arctic amplification (ratio of the Arctic to global temperature trends) is not a constant but varies in time on a multi-decadal time scale, (b) the Arctic warming from 1910–1940 proceeded at a significantly faster rate than the current 1970–2008 warming, and (c) the Arctic temperature changes are highly correlated with the Atlantic Multi-decadal Oscillation (AMO) suggesting the Atlantic Ocean thermohaline circulation is linked to the Arctic temperature variability on a multi-decadal time scale.

    Comments anyone?

  41. 141
    Bill DeMott says:

    Good points, Nick O.

    Aren’t there a lot of areas on the continental shelf where the depth of the water is more like tens of meters than hundreds of meters?

    At what depth could surface warming affect ice on the sea floor?

    Same for sunlight. How deep till sunlight penetration becomes insignificant (or how shallow till it can becomes significant)?

    Comment by wili — 20 Jul 2009 @ 2:54 pm

  42. 142
    Bill DeMott says:

    At what depth could surface warming affect ice on the sea floor?

    Same for sunlight. How deep till sunlight penetration becomes insignificant (or how shallow till it can becomes significant)?

    Comment by wili — 20 Jul 2009 @ 2:54 pm–

    Will–Here is a basic point about ice–it’s ligher than liquid water and therefore ice floats. There is no ice on the bottom of the sea or lakes.

  43. 143
    Hank Roberts says:

    I think Wili was asking about methane hydrate ‘ice’ — which is actually mostly below the seabed, though some is exposed. On that, this may help:
    http://scholar.google.com/scholar?q=methane+destabilization+warming

  44. 144
    tamino says:

    First, J. Bob (#85) wanted to use sea ice data to claim “Global sea ice still running about normal, no mass meltdown.” He was ridiculed, and rightly so, because the very graph he linked to showed the folly of his statement. Michael Sweet put it rather well in #93: “Are you suggesting that the uiuc graph you linked to shows ice running about normal? Fit a line to the data. It is obvious even from a cursory examination that the ice has declined in the past thirty years according to the linked graph. Looks like you bungled it again.”

    Then, J. Bob (#101) said “One can look at a graph in many ways,” followed by more extremely silly talk, all of which reminded me of the “pathological liar” skit on Saturday Night Live. Probably the most embarrassing statement of all was “If you look at the anomaly from beginning of 2008-now, it trending up.”

    I guess he decided that nobody was going to believe his ridiculous claims about the sea ice data, so he’d lay the groundwork (in #103) for questioning the data itself with “does anyone have a handle of just how accurate the data we are discussing is?” He followed through in #138 with “Seems that before one can use statistics, effectively, one has to have an idea of the quality of the data. Statistics will not improve the smell of garbage coming in to garbage going out.”

    He’s only shown how little he knows about statistics. Imprecision in data doesn’t create false trends, especially at the extreme (and I do mean extreme) level of significance of the downtrend in global sea ice. If the data were 1,000,000 times less precise, then it would mask whatever trend might be present — but it would not create the statistically significant downtrend which is present in the data. Clearly. To everybody except those who refuse to see.

    J. Bob: there is indeed a smell of garbage here. But it isn’t from the sea ice data.

  45. 145

    Steve L, thanks for the clarification.

    Good luck with your inquiries on tides.

  46. 146
    Thomas says:

    Steve, if you do back of the envelope -order of magnitude size estimates you’ll discover that tidal heat dissapation is a trivial part of earths energy budget. Now tidal dissaption goes down at a high rate as distance increases (a lot more than inverse squared). So during the first few hundred million years the planet had the moon, it might be an important term -but we have so little geological data that early, that we only know the most approximate things about the climate then. It might make an interesting study to determine what it might have contributed back then, but it is hardly relevant to modern climate science.

  47. 147
    Eli Rabett says:

    One of the problems with Northern Hemisphere ice extent is that it includes fairly large areas that are going to melt for sure and which are really not connected to the polar cap such as Hudson’s Bay. This means that the maxima are not as useful as you might think

  48. 148
    Doug Bostrom says:

    J. Bob 20 Jul 2009 at 8:29 pm:

    “…uncertainties in the orbital trajectory, the vehicle attitude, pointing of the antenna, beam errors, after that the signal is quantized (another error/uncertainty), and transmitted back to earth. In addition you have long term aging of the components, equipment temperature gradients, radiation effects, etc. All of these effect the accuracy of the data.”

    Good point! If all those error sources are significant and in sum are biased in one direction, in reality we could be looking at even –less– ice remaining than the trend line suggests!

    Fortunately it seems unlikely that the summed error points in one direction, plus unlike us punters I suspect the folks that run the measurement program are on top of this. What a relief, eh?

  49. 149
    Doug Bostrom says:

    I should clarify my last remark, 20 Jul 2009 at 11:33 pm.

    Of course there will be errors from some of the sources J.Bob mentions, and it’s actually unlikely they sum to “0″.

    Do they all exhibit a bias in one direction? Probably not.

    Will the sum of the errors exhibit a strong but unnoticed bias in one direction? Probably not.

    Why? Because the operators of the equipment are almost certainly not going to overlook significant error sources.

    If the operators were overlooking significant errors, would we have cause for celebration, or despair? I guess that depends on the error, and your perspective.

    For the curious, complete information on the collection of this data and associated significant limitations is here

    http://nsidc.org/data/docs/daac/nsidc0051_gsfc_seaice.gd.html

    including an extensive set of references to articles going into the more fine-grained behaviors and limitations of the instrumentation behind the datasets. It does not look like many loose ends have been left hanging.

  50. 150
    Chris Dudley says:

    The comments on the guest post by Kyle Swanson appear to be closed. But I did a little more work after my comment #50 http://www.realclimate.org/index.php/archives/2009/07/warminginterrupted-much-ado-about-natural-variability/#comment-130960

    I am now pretty certain that the jump in temperature between 1997 and 1998 shown in the second plot is around 2 sigma in inter-annular variability rather than better than 3 sigma as stated in the post. In the GISS data it only appears to be around 1.5 sigma so it is a pretty typical change.

    I suspect that a sigma derived from another data set may have been used to do the calculation described in the guest post. In any case, the jump does not appear to be anomalous within the presented data set.


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