This is getting silly. Maybe scary is better. CT’s Northern Hemisphere sea ice area anomaly used to go down to -1.5 Million Km2.
Back in June/July, they had to change the graph and add a white bit to the bottom, to allow for the unusually low numbers, so they stretched thw white bit to -2 Mill.
Then a month or so back, it went to -2.5Mill.
Just last week (thanks for the heads up, Steve), thanks to the fact that the ice still isn’t there, when it should be, even more white was added to the bottom of the graphic, to allow for the new lowest ever anomaly of -2.7 Million Km2.
Here is the ‘tale of the tape‘ as it currently stands. Aw, shucks, the darned needle’s gone and fell right off the bottom again. Below -2.7 Million Km2.
Two obvious things to note here. First, the way the loss of sea ice has fallen below long-term averages this year has caught out the team at CT (who know much more about the subject than amateurs, like me) not once, but four times, in six months. Second, the only increase in white stuff as far as the Arctic sea ice is concerned is the extra white sections being pegged onto the graphs to allow for the ever-increasing anomaly.
There’s a chance for a good old-fashioned spread bet here. How much extra white space should CT add to its anomaly graph this time? Will -3 Mkm2 be the limit of the anomaly between now and next Spring? Anyone care to take a punt at -3 to -3.5 Mill.? I might be tempted to offer odds against a spread of -3.5 to -4 Mill. between now and April, but someone might want to take the spread even further. Is this as far as the anomaly will go this year?
I’d like to know what readers are willing to suggest will be the largest sea ice anomaly of 2007, and the largest anomaly between October 1st, just gone, and April 1st 2008. I’ll publish my forecast in a couple of days time.
Oh: and here, for the sake of completeness, is the NSIDC briefing from October 17th. I’ve emailed to ask what their measurement system shows the anomaly as. The comment below is from that briefing:
The differences from climate norms for the previous century continue to increase, even though the 2007 melt season has ended and the ice has begun its seasonal recovery. As of October 16, the extent was 3.20 million square kilometers (1.23 million square miles) below the long-term average.
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October 20, 2007 at 2:30 am
Steve Reynolds
Fergus, do we really know how unusual this is? There is some data showing that the artic was pretty warm in the 1930s and 1940s…
October 20, 2007 at 8:52 am
fergusbrown
Steve, we don’t really know, because there isn’t enough historical data to be confident about past conditions. Most specialists seem comfortable to say these days that at least some of the Arctic was warmer in the 1930s/40s than it is today. In the absence of observational data, one solution is to consider human comparisons between times (as the ACIA did, for example). AFAIK, there aren’t many natives of the Polar regions who have said that this all happened in Grandma’s day, so my current opinion is that the changes we have seen since 2002 are probably greater than at any time since at least the Middle Ages. The loss of perennial sea ice in the central Arctic basin may be completely unprecedented.
A look at the CT regional graphics currently shows a marked absence of ice in several area where it should be possible to compare conditions with historical records, such as Hudson Bay, Newfoundland and The Chuchki Sea. It might be worth looking at records for the inhabited areas, where they are available, to see if there are previous occasions when the refreeze still hadn’t started in the middle of October.
October 20, 2007 at 11:10 am
Ian Hopkinson
Cryosphere Today has some datasets stretching back to the late 19th century with some provisos on accuracy as you go further back, image:
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seasonal.extent.1900-2007.jpg
Data here:
http://arctic.atmos.uiuc.edu/SEAICE/
Tamino also posted on this recently, including data from both hemispheres:
http://tamino.wordpress.com/2007/10/08/sea-ice-north-and-south-then-and-now/
(Stoat cautioned heavily on the older southern hemisphere data - and he should know)
I wouldn’t draw any conclusions regarding the re-scaling of the graph - it’s standard practice to keep the axes pretty tight to the data and it’s not like you’re drawing these things out with a pencil anymore.
Although this year has been pretty exceptional, it is just a single year and if you look back over the satellite anomaly record there are some pretty big drops followed by recovery. It’s true there is a clear downward trend, but I wouldn’t interpret this as a serious acceleration yet.
October 20, 2007 at 12:09 pm
fergusbrown
It’s not so much conclusions as observations at this point, Ian. It’s hard to argue that this year’s decline doesn’t stand out in the satellite record. The long-term decline in perennial, or multi-year ice, is also a measured phenomenon. In the absence of reliable precedent, we can still operate with the data we have and the (broad) model output which has projected Polar amplification of GW for years now.
It really is very difficult to keep entirely away from the tentative conclusion that what we are seeing (probably since about 2000) is prima facie evidence that GW is starting to have at least one of its projected impacts.
In a sense, we’re back to the timescales question again, here. A declining trend of 8-10% per decade is rapid enough, but within the kind of pace that a climate or crysphere specialist might be able to anticipate. A 30% decline in a single jump doesn’t imply a sudden acceleration in itself, but the difference in the rate of decline is still very noticeable.
Shindell’s recent paper on seasonal responses to ozone in the Arctic is worth considering here. It’s one example of a plausible connection which could help us understand the dynamics and project the trend of future losses more reliably. In a few days, i may post a projection for the coming seasons, just for fun.
October 20, 2007 at 12:51 pm
S2
I’ve been watching the “tale of the tape” for a while, now. I didn’t notice the axis changing back in June/July though, and I’m a little surprised at this (since there appear to have been 4 “dips” below -1.5 MKm2 in 2005/2006).
In an attempt to use something other than a random guess, it looks to me as though the largest differences between a peak and a following trough is in the order of 2Mkm2 - so I’ll guess that -3 Mkm2 should be enough (but not with a great deal of confidence).
So, -2.9 sometime in the next two weeks; reducing to -1.25 before the end of April.
October 22, 2007 at 12:05 am
Steve Bloom
CT obviously has some software problems with that annual graphic, since it appears to have been basically patched at the bottom. It was never very accurate since the line and dashed line spacing was inconsistent. That said, eyeballing today’s graphic seems to indicate that the anomaly is at about -2.95. Fergus, do they provide an actual number somewhere on the site?
I’d be curious to know what the models show for winter sea ice extent when summer extent is down in the present range. Is there actual open water, or is it just thin, delicate ice that goes away quickly once the sun returns? Intuitively I would expect that any area without sunlight is going to skin over until things warm up more, and as Fergus noted it may be that the constrained geopgraphy will mean not much of a reduction of winter extent under such circumstances, but intuition is these things is of little value.
Ian, FWIW note that all of the experts had concluded before this year that a sudden acceleration had commenced about 2000 (more or less the year in which the prior models began to go off the rails). That’s why this summer we began to hear normally-taciturn scientists begin to use words like “breathtaking” to describe what’s going on. It’s true that there have been past anomaly fluctutations that have been on nearly the same scale in absolute terms, but I think the more important thing to consider is that this summer a huge area of open water appeared that has not been seen before (a fact which is reflected in the percentage anomaly decrease seen this year). I think it would be useful for you to use the NSIDC monthly graphics to compare between this September and one of the past months with a similar absolute drop (IIRC there’s one previous September that qualifies).
October 22, 2007 at 1:37 pm
fergusbrown
I’ve always been a bit uncomfortable with some of the graphics for anomalies on CT, Steve, but that doesn’t make the site hugely convenient as a reference point. There are no number available on CT; my figures are extrapolations from the graphics, unless they have specifically cited a number in an editorial.
The CT raw data is from NSIDC, which has recently provided an explanation of how area is calculated from extent, by giving partial values to data grid boxes with less than 100 sea ice cover; I suppose we could do something similar if we wanted to, though I bet it’s harder than it sounds.
I’ve no idea how well the models will be able to respond to the decline this year, as it is so far out of the normal range, but I imagine that the ice will form in most of the Central Arctic, as per usual. Thin? I suppose, by past standards, 1-2 metres is ‘thin, delicate ice’. As a consequence, severe Winter storms can bust it up and move it around a lot more easily than the thicker perennial ice; there could be time this Winter when the Bering Strait opens and closes like a barn door (though I don’t know for sure).
If this Winter is going to see a below average sea-ice area, it will largely be because of the areas outside the Central Arctic, like the Bering Sea, Okhotsk, Hudson, Labrador, etc., may not freeze over as completely as they would otherwise have. As this would be a continuation of the experiences of the last few years, it is possible.
October 22, 2007 at 8:32 pm
Steve Bloom
Today is at about -3.1, with the caveats noted above.
Regarding the prior models, I should have been more clear that I was wondering how they showed winterice behavio at a time when the summer ice behavior was projected as similar to what we saw this year. OTOH it’s probably better to wait for the next iteration of the models.
October 22, 2007 at 11:15 pm
S2
Are we talking about the same graphic here? The tale of the tape (which is what the one I thought we were talking about) currently shows about -2.8, I think?
October 23, 2007 at 4:59 pm
Steve Bloom
Aha, I hadn’t realized they had extended the “tale of the tape” graphic but not the monthly one. I certainly see the -2.8, but if you look at the left side of the monthly one the area is about 5.9 and the anomaly is about -1.4. Looking at the right side, the present area is about 4.3 but the anomaly has fallen off the bottom. Since the zero line of the anomaly doesn’t change, I derived the current anomaly by taking the difference in area and adding it to last year’s anomaly. I can’t see that I’m doing anything wrong, but obviously there’s a discrepancy with the “tale of the tape.”
October 23, 2007 at 9:03 pm
S2
Glad you cleared that up, Steve - thanks.