26 June 2013

2013 Sea Ice Estimates

Our June guesses for 2013 are 3.9, 4.1, and 4.4 million km^2 for September monthly average sea ice extent as computed by NSIDC.  See the ARCUS SEARCH Outlook for the full current collection of estimates.

Again, I'll put our estimates in context of some other estimation methods. 

  • Climatology 1979-2000: 7.03 million km^2
  • Climatology 1979-2008: 6.67 million km^2
  • Linear Trend Climatology 1979-2008: 5.15 million km^2
  • Wang, Wu, Grumbine model: 4.4 million km^2
  • Wu, Grumbine, Wang model: 4.1 million km^2
  • Grumbine, Wu, Wang statistical ensemble: 3.9 million km^2
All three of our estimates are well below what they were last year -- 4.9, 4.8, and 4.4 million km^2, respectively.  For the two model-based estimates, this is because the model has continued to thin its ice cover, and that ice cover is less extensive.  Then the model (which is coupled air-sea-ice) is not seeing any reason for the ice to be getting markedly thicker or more extensive.

The statistical ensemble reflects two items.  One is, last year being a new record, well below the estimate (by 0.8 million km^2), pulled down the best curves that can be fit through the data.  The second is, the curve itself shows a zone of steep decline.  This is where the feedback of more open water -> warmer ocean -> thinner ice -> easier to melt ice -> more open water in summer is starting to take off rapidly.  (If the basis for my using this curve is reasonably correct, that is.)

The linear 'climatology' estimate last year was 5.23 million km^2, versus the observed 3.61.  Too high that year, and every year 2007-2012, and very likely many more to come.  Merely points to a straight line not being a good representation of how the ice pack is changing, which is no surprise.  But it is also a reminder that talk of sea ice 'recovery', which will no doubt occur in some corners when (if) 2013's extent is greater than 2012's, is nonsense. 


Hank Roberts said...

I notice there's no prediction from wuwt in July: http://www.arcus.org/search/seaiceoutlook/2013/july

WUWT did show in June: http://www.arcus.org/search/seaiceoutlook/2013/june
right next to the Naval Research Lab/Posey prediction

Kevin O'Neill said...

This is where the feedback of more open water -> warmer ocean -> thinner ice -> easier to melt ice -> more open water in summer is starting to take off rapidly.

This is generally held to be true in the Marginal Ice Zones on the periphery of the ice pack. This year has seen a lot of floe-filled open water north of 80. Would you expect the process to be the same - or very similar - in the areas north of 80?

Robert Grumbine said...

I'll have to write up our July updates. One of the models went for an increase in September's cover. Could be a reflection of the slower than 2012 decline in June.

The law of conservation of energy doesn't care about latitude, so the feedback will work north of 80 no less than south. At the highest latitudes, the sun isn't very far above the horizon, so the contrast between ice albedo and water albedo (reflection of the sun) isn't as large -- at low angles the ocean is much more reflective than at high sun angles. Still not as reflective as sea ice, even sea ice with melting snow. So, as a mechanism, this will still operate -- if there's open water.

But if you're looking at relatively raw figures from passive microwave satellites, you need some caution. On the thicker ice, the snow pack melts and can create ponds on the surface. To a passive microwave satellite, the ponds look the same as the ocean (give or take a little). But in terms of this feedback, ponds are not 'open water'. Energy absorbed by them is still going to melting the ice floe, rather than heating the ocean. So, if you are indeed looking at this source, what you could be seeing is not so much a matter of more open water in the ice pack, but more melt ponds than usual.

The melt pond issues are one of the reasons why the sea ice extent is a more reliable number than sea ice area.

Kevin O'Neill said...

Ever since the spring cyclone Modis has shown areas near the pole we would call Marginal Ice Zones if found on the periphery.

The areas of lowest concentration (not melt ponds) can be found between Franz Josef Land and the pole. http://neven1.typepad.com/.a/6a0133f03a1e37970b01901e58acbd970b-800wi

IMB buoy 2012J is located in the low concentration area (Pos: 87.12 N, 12.84 E). I really don't have a clue how to interpret thermistor string data, but buoy 2012J seems to show more than a meter of bottom melt since June 1st. CSV file here: http://imb.crrel.usace.army.mil/irid_data/2012J_clean.csv

Robert Grumbine said...

I'd be conservative about that image. It was clearly stitched together from many passes (necessary) and there are scan artefacts in the image (seams along scan track edges). You've also clearly got clouds just off the pack, and it's unlikely they stop right at the edge. I agree that it's probably low(er) concentration sea ice in the area you're suggesting, which would be invoking the feedback I mention.

The link you point me to shows only about 10 cm of snow melt, and the ice thickness stopped reporting on June 19th, by which time ice thickness was down perhaps 30 cm from its maximum. It's plausible that it's continued to melt, and could be down by a meter by now, but this isn't an observation of such melt.

The air temperature gauge is clearly having problems. Air was warming up towards freezing through late May, but since then, it is reporting temperatures declining, even as solar incoming has been increasing and snow melting.

The very solid conclusion: Data are messy.
Less solid, but pretty good: There's an area of reduced concentration sea ice in the European Arctic.

Passive microwave, so use some caution (see #1), with animations and comparison to last year: http://polar.ncep.noaa.gov/seaice/nh.html Suggests that the feature has indeed been persistent for some time. Something wrong with the permissions at http://polar.ncep.noaa.gov/seaice/Historical.html, but when fixed it'll let you look at monthly animations.

Alastair said...

Hi Bob.

Can you comment a little more on your remark:

The melt pond issues are one of the reasons why the sea ice extent is a more reliable number than sea ice area.

I don't see why.

Robert Grumbine said...

Always happy to give more detail. The melt ponds can only cover a portion of the surface of the floe. If the pond reaches all the way to the edge, it drains in to the ocean and stops being a pond. (At least until it shrinks enough to not be out to the edge of the floe.)

So it's relatively easy to tell that _some_ of that area is ice, which then gets counted as extent. But it's hard (because passive microwave can't distinguish between ocean and melt pond) to tell just _how much_ of the area is ice, plus melt ponds on ice, instead of ocean.

Aside: The link http://polar.ncep.noaa.gov/seaice/Historical.html now works for getting animations of previous months.