Wednesday, April 7, 2010

Arctic Sea Ice Updates

Seems unfair for everybody else to have all the fun, so here are a few thoughts about the Arctic sea ice. This is partly prompted by Hank Roberts question about the ice.

The starting point in data is the observation that for the first time in many years, the sea ice extent for the Arctic was recently close to the climatology.  Even spending most of the last 4-6 weeks less than 2 standard deviations below climatology.  On the scale of observations, this is hardly terribly exciting -- a few days that were close to what had been the norm, and a month that was not drastically below normal (2 standard deviations below normal means below 98% of all observations).  March, for the month, nevertheless, was below normal:
NSIDC trend line for March.


So how do we reconcile the two observations -- one of a few days being near normal and the other of a monthly trend continuing, and monthly average being below normal?

As you'd expect, we pay attention to more than one thing at a time, and we remember that weather is not climate.

On the weather and climate side, a few days can be quite deviant from the norms.  Here near Washington DC, we've been 30 F above climatology yesterday and today (17 C).  Quite an extreme excursion, but it'll be cooler tomorrow and is forecast to be back about normal on Saturday.  Same sort of considerations apply to sea ice extent, and, less so, area.

Remember that extent is that we add up all grid cells in our analysis which have more than 15% of their area covered by ice.  In area, we add up only the area that is covered by ice.  For a number of purposes, particularly in summer, extent is much more reliable a figure than area.  But about this time of year, that's less the case, and you can have large fluctuations in a few days.  The monthly average, however, is less concerned with a few unusual days.

More than one thing going on at a time is a different part of the story.  In thinking about there being an ice cover, there are two things that we have to pay attention to.  One is freezing and melting -- if you freeze lots of new ice, you have greater ice extent.  If you warm up, you melt off the ice and have less ice extent.

On the other hand, if you blow ice towards open water, you also increase the ice extent.  At least you do until the ice melts.  One thing that can happen is to set up a 'conveyor belt' -- freeze ice in one area, and blow it towards another.  That has some interesting effects on the ocean.  You can also greatly reduce the ice extent for a few days -- have the winds blow the Arctic ice back towards the north pole.

In March (see the NSIDC story), it looks like both a cold spell (freezing ice in the interior) and conveyor (carrying the ice towards the edge and expanding the edge) set up for a while.  I'll leave it to others to check WUWT and the like to see whether they're as fond of wind as an explanation for the brief approach to normal ice conditions as they were with it as an explanation for the record minimum of 2007. If they are honest, they are touting winds just as strongly now as before.

Scientifically, winds being involved were no news.  Winds are part of the climate system, along with temperatures.  We (folks who look at sea ice) always knew that.  It's always better to nail down just how much is going on due to each cause, so people write that up in the scientific literature. 

So my guess for where we are in the Arctic: The ice formed by late season freezing and conveyor belt is thin.  There has not been time for it to freeze thickly, nor for it to get mechanically piled up to be thick.  The expansive winds that lead to the increase in extent also mean driving the ice towards warmer water.  If the current pattern of blowing the ice out towards the edge were to be sustained, it points to a temporary high value for extent, and then a rapid drop in extent as the ice melts, or as winds reverse and compact the ice pack.

Whatever the details, still no reason for me to change the prediction method I used last year for guessing the September average extent.

In the mean time, go here for animations of the last 30 days sea ice.  And over here, you can see animations by month.  Lots to be desired in both places, not least that the color bar and flag values change over time, as does the satellite data source.  Still, it gives a feeling of what weather can do to the ice pack.

11 comments:

wattsupwiththat.com said...

"If they were honest, they would be touting winds just as strongly now as before."

Well gosh, two can play the honesty labeling game.

If you were "honest", you would have read stories in the last week at WUWT that talked about wind in the Arctic rather than leaving it to others and applying your dishonesty label. There are several mentions of wind and the Arctic issue.

For example, if I was "dishonest" I could have removed the mention of wind from two posts from NSIDC for example, one from the Arctic sea ice news, another from Dr. Walt Meier of NSIDC which I solicited from him.

Two mentions of wind being the driver of the current event, what's your mentions threshold for "dishonesty"? 3, 5, 10, 100?

The need for labeling people "dishonest" because they don't meet some imagined internal threshold, or simply because you didn't look close enough is telling.

Oh and let's not forget this one. As part of the "dishonesty" you apply to me, a number of people suggested that NSIDC made recent adjustments to the sea ice extent. I defended NSIDC, (see TheGreat Imaginary Ice Barrier post) because apparently, defending facts is what "dishonest" people do.

I really dislike such sloppy generalizations as you have made. We'll see if you can do the right thing and correct your error.

Otherwise I agree with you, Arctic wind has made some significant short term differences, such as contributing to the 2007 record low extent. The collection of wind patterns long-term indeed becomes part of the climatology.

Penguindreams said...

If you're going to use 'I', you should attach a name. More than 1 person writes at WUWT as far as I know.

I've clarified the language a little. I made an assertion about what readers would see if WUWT were speaking honestly about sea ice. If they see that, then it's a positive sign. If they see otherwise, they can conclude otherwise. But I leave it to readers to decide for themselves. WUWT was certainly speaking vigorously about dismissing the 2007 minimum as merely being wind. Did the same vigor apply to the more recent news? Readers may decide.

It is quite strange, however, to see someone from WUWT complaining about mention of honesty, given the frequent articles that WUWT runs which attack the honesty of scientists who are attempting to understand the climate system. Perhaps you can take up, and correct, your prior attacks on scientists working with the surface record. See, for example, work at open mind which managed to reproduce the warming trend that you (WUWT) were saying was fraud.

Gareth said...

You might want to put a "width=x" (where x is the pixel width of your main text column) statement inside the < img > tag for your March extent graph, because at the moment it disappears under the right sidebar. Like a joke lacking a punchline... ;-)

Paul said...

Joe Bastardi was touting the return of the ice in the hilarious Colbert bit on weathermen vs climate scientists last night.

Paul Middents

Deech56 said...

Penguindreams wrote: "See, for example, work at open mind which managed to reproduce the warming trend that you (WUWT) were saying was fraud." I hope you get an answer - I asked that in an open thread at WUWT and seem to have lost posting privileges, and a poster named "barry" was also apparently banned for asking for a comment on Tamino's work (replicated independently by others) at WUWT.

The idea of independent replication (as opposed to "auditing" - checking the calculations) seems to be a concept that is not well understood by the average reader.

Hank Roberts said...

"... a pulse of fresh water into the Arctic ..."
http://www.nature.com/news/2010/100331/full/464657a.html

Hank Roberts said...

Here's a site that needs an intervention; they're trying to organize an anti-global-warming campaign (their honorary chief is columnist George Monbiot, notable last week for his attacks on Phil Jones).
http://www.campaigncc.org/climate_emergency

They're using the 2007 sea ice chart, and links to stories about total loss of summer arctic sea ice in five years, to recruit people.

------
“I have no trouble with my enemies. I can take care of my enemies in a fight. But my friends, my goddamned friends, they're the ones who keep me walking the floor at nights!”
-- Warren G. Harding

Hank Roberts said...

specifically, they're using this chart

http://www.campaigncc.org/sites
/www.campaigncc.org/files/imagepicker/p/padraic/icegraph.jpg

on this page:
http://www.campaigncc.org/climate_emergency

to illustrate this point, which is generally correct I think:

"There are long periods between new reports and the science used in the reports may already be somewhat dated even when the IPCC report first appears. That means that in a situation where the science is evolving and changing very rapidly the primary scientific report on which policy is based can often be out of date."
(chart through 2007 of Arctic summer sea ice)

Hank Roberts said...

http://psc.apl.washington.edu/ArcticSeaiceVolume/images/BPIOMASIceVolumeAnomalyCurrent.png

hat tip to L. Hamilton at RC:
http://www.realclimate.org/index.php/archives/2010/04/second-cru-inquiry-reports/comment-page-11/#comment-171624

jyyh said...

Hello, it's me and my stupid questions... In your opinion, is this april's pattern of antarctic sea ice anomaly going to be dominant during the times when West antarctic glaciers melt ? ref: http://nsidc.org/data/seaice_index/images/s_anom_hires.png

Penguindreams said...

jyyh:
Sorry about the delays. April looks fairly normal. Hitting exactly climatology is quite rare. The usual is a pattern like what you see here of more ice than usual on one side of the Antarctic peninsula, and less on the other. What changes is whether it's the Ross or Weddell that has more ice than usual.

West Antarctic glaciers, I don't expect to have much effect on the sea ice coverage. If the West Antarctic ice sheet started melting in a big way, it might expand the sea ice pack. The melt water is fresh. That will stabilize the water column and help prevent warmer waters that lie deeper down from melting ice at the surface. What I can't say right now is how fast the melting would have to be to have this effect.