Sea ice thinner?

Since this years sea ice failed to be a record min (how careless of it) there is a sense of furtive scurrying around looking for something else; and DSB is looking at record thin instead: Sea ice in the Arctic Ocean has melted to its lowest volume in recorded history, according to new measurements they say on 7th october. Interesting.

Volume implies measuring thickness. But while measuring area from satellite isn’t too hard (people have been doing it routinely for years, and there are problems, especially when its wet, ahem, but still no-one is too worried), measuring thickness is much harder. Here is some stuff; note that it suffers badly from over-PR-ing in its abstract: though only about measurements it feels obliged to vapour on about prediction. What you can’t get from just that abstract is that measuring the thickness via altimetry is rather imprecise, especialy when the ice is thin: something like 0.5m accuracy at best. You can also try to “measure” thickness via microwave emission and guessing the ice temperature and estimating heat flow and modelling and hence guessing thickness; this is also imprecise. Or you can measure it by sonar from submarines; this doesn’t give you enough coverage; or drilling holes; this is even worse.

No matter. Lets follow the DSB trail, to http://dsc.discovery.com/news/2008/10/07/arctic-sea-ice.html?dcitc=w01-101-ae-0003. The headline is “Arctic Ice Thinner Than Ever Despite Cold Winter” but the text is “the ice may be thinner than ever.” And that leads you to http://dsc.discovery.com/news/2008/08/27/arctic-sea-ice.html . And that, in its turn, says f*ck all about ice thickness.

Backing up one, we have Walt Meier of National Snow and Ice Data Center in Colorado and colleagues say the overall ice volume in the Arctic Ocean is at least as low as 2007, they say, and may even have dwindled more by as far as 10 percent. but no link to a source or any data. And The latest measurements are preliminary, though they seem to confirm Zwally’s suspicions. However he stressed that scientists will have a better handle on the situation later this year, once the data are in from the ICE Sat satellite, which is currently taking readings of ice thickness from orbit.

Hmmm.

Walt Meier’s home page leads to http://nsidc.org/data/seaice/ which doesn’t mention thickness.

Ah well. Its quite likely the ice was thin this year: first year ice usually is, and there was a lot of first year ice about. But don’t believe the “measurement” tag, unless people are prepared to point oyu towards the actual measurements.

Comments

  1. #1 Eli Rabett
    2008/10/08

    Eli suspects that US UK and Russian navies know a lot more about the ice thickness than anyone else and they ain’t telling.

    [Its possible, but I doubt it. They had a very restricted interest: the ice in the corridors they liked to patrol. They have no particular motive for not releasing the data, other than general paranoia. We already know where they go -W]

  2. #2 Steve L
    2008/10/08

    DSB doesn’t do much in the way of detailed scientific stuff. It’s not their thing, so when it comes to science they tend to stick with links to headlines. Go to NSIDC and see the title of their news release:
    “Please see the NSIDC press release, “Arctic Sea Ice Down to Second-Lowest Extent; Likely Record-Low Volume” for a detailed analysis of this year’s Arctic sea ice minimum and a synopsis of the 2008 melt season”

    I don’t know why you characterize it as furtively scurrying. Why scurry about when the negative trend in sea ice extent steepens when 2008 is included (despite having a higher minimum than 2007)? I agree with your conclusion about seeing actual measurements, though.

    [I guess you mean this? There is an awful lot of blather there, but precious little content. They have no thickness data; the best they have seems to be fig 4, which is a proxy of age. Meier says Warm ocean waters helped contribute to ice losses this year, pushing the already thin ice pack over the edge. What the f*ck is this supposed to mean? Pushed it over the edge of what? They should get back to doing science and stop whoring for the PR people, because they aren't good at it (thankfully) -W]

  3. #3 Hank Roberts
    2008/10/08

    Did I manage to post an excerpt from this

    http://www.esa.int/esaEO/SEM6MB9FTLF_index_0.html

    maybe I lost it, FF 3.0.3 has been crashing. See link for
    ——–

    “NIC Chief Scientist Dr Pablo Clemente-Col√≥n … via email from aboard the US Coast Guard icebreaker Healy in the Arctic, where he is conducting joint mapping operations with the Canadian Coast Guard….”

    He’s talking about ESA using active radar satellites to look at ice thickness — I infer he’s up there looking at actual measurements to correlate with whatever the satellite radar produces, but that’s just, you know, their PR working its way with me I suppose.

    [Oh yes. Thats the stuff thats 0.5m at best, and that only on unbroken ice. The water signal dominates when given the chance -W]

  4. #4 Steve L
    2008/10/09

    Hi William, yes I did mean that. The headline is: “…likely record-low volume”. They didn’t have data for it, but they had reasoning (or blather or arm waving), and as you note at the end of your post, it may well be likely. I don’t know if that means ‘likely’ in an IPCC sense, but just as long as it means ‘more likely than not’ then I think DSB is fine in pointing people there.

    Focussing now on NSIDC — how do you mean they’re whoring for PR people (like DSB)? What’s their motivation for that? I’m not an apologist, and if statements like Meier’s are part of a pattern, I’ll be glad to learn about it. (Excuse my ignorance if you’ve posted a lot of this in the past; I became a regular visitor only recently.)

    [By PR people, I meant their own institutes, not DSB. Motivation? I'm not sure. Fame, probably. The desire to say something. Its quite hard to sit still and say nothing when other people are talking (is that a mirror over there?). But the problem, alas, is that saying "well this years ice was a bit more extensive than last year, and probably thinner because it was first year ice, and we don't know what will happen next year" is too dull to report. "pushing the already thin ice pack over the edge" is meaningless blather, but sounds exciting, so gets in. Sigh -W]

  5. #5 crandles
    2008/10/29

    http://www.esa.int/images/GRL-fig1-8cm_mean_L.jpg
    presumably from Giles et al
    Circumpolar thinning of Arctic sea ice following the 2007 record ice extent minimum

    I guess this isn’t inconsistent with your ’0.5m accuracy at best’. Lots of ‘plummets’ and ‘record’s in headlines while your post could be mistakenly be taken to mean the headlines could/should be rewritten as declining thickness just about detectable for first time in records going back all of six years and is therefore a poor measure of how exceptional the summer 2007 melt was.

    [0.5m is for each pixel -W]

    If I am guessing correctly; if the accuracy is 0.5m at best for a single location and the satelite measures at many locations (how many? a few thousand ??), then the accuracy of thickness for whole area comes down to the 5cm error bars on that graph?

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