Arctic Sea Ice

Arctic faces

Apparently we human beings have a brain that is specialised in understanding and interpreting faces. Carl Sagan believed we are "hard-wired" from birth to identify the human face because it increases our chances of survival if we're able to discern friend from foe quickly. This allows people to use only minimal details to recognize faces from a distance and in poor visibility but can also lead them to interpret random images or patterns of light and shade as being faces (a psychological phenomenon called pareidolia).

A very famous instance of pareidolia is the Face of Mars, and not a week passes by where somewhere around the world someone claims to have seen the face of Jesus Christ in some object or other. They see them on Google Earth images, ultrasound pictures, pieces of pizza, Sussex hawthorns, chicken feathers and IKEA toilet doors. What, you've seen the Lord's face in some shroud? Boring!Look what I saw when I opened a jar of Marmite this morning.

I'm not writing this blog post to inform you that I've seen our Saviour's face appear somewhere in the Arctic sea ice (although I probably could if I wanted to), but it is definitely funny to see facial patterns when looking closely at the MODIS satellite images. Here are some examples:

Ice thickness models

One of the most intruiging and elusive aspects of Arctic sea ice is its overall thickness, and by implication the total volume of sea ice. The bigger the volume, the longer it will take for the Arctic Ocean to become effectively ice-free in summer. Unfortunately, despite many different kinds of data, no one can tell for sure what the current status is, except that volume has decreased significantly over the past decades.

Satellites could provide more definite answers, but we are currently in a gap between ICESat and CryoSat-2. ESA and NASA are doing a fascinating job in the Arctic gathering data which will be used to calibrate the latter as we speak. In the meantime we fill the time by speculating, and a big part of that speculation is fueled by ice thickness models.

The best known models in Arctic sea ice amateur circles are PIPS 2.0 (Polar Ice Prediction System), PIOMAS (Pan-Arctic Ice-Ocean Modeling and Assimilation System) and TOPAZ (Towards an Operational Prediction system for the North Atlantic European coastal Zones). Although model output is not as good an approximation of reality as actual data - to put it mildly - it is still interesting to look at.

A warm river runs through it

Never a dull moment, always something new to see and learn!

I'm eyeballing the Arctic sea ice graphs page several times a day and noticed something new the day before yesterday while eyeing the Arctic SST map from the National Centers for Environmental Prediction (NCEP), run by climate scientist and blogger Robert Grumbine (the sea ice and sea surface temperature groups, not NCEP itself):

It struck me that the river surface temperatures of some of the Russian rivers were anomalously high (as much as 8 degrees C in some places), which isn't that remarkable of course when you consider the air temperatures on that side of the world, which have been high for quite a while now:

The intruiging thing, when you think about it, is of course that the water of these warm Russian rivers eventually ends up in the seas on the Siberian Coast. Two of the rivers that light up red and crimson on the NCEP SST map, the Ob and the Yenisei, flow out into the Kara Sea. The third one, the Lena, empties into the Laptev Sea. What happens when that relatively warm, fresh water reaches the icy shores? Is there an effect on ice melt, now that the melting season has started?

Flushing out the Fjord 2

This is a brief update to the first Flushing out the Fjord post.

It looks some more ice is being flushed out of the Illulisat fjord. Here's an animation of the past week:

Although it looks quite spectacular, this isn't as uncommon as I suspected it to be. I'm going to look some farther back when I've mustered enough courage to dive into the archives, but I did find an image dating from 2009 (coincidentally on the second day the MODIS satellite images could be viewed online, March 19th):

Temps

Air temperatures

One thing I failed to mention in the last SIE update and promised to get back to, is the fact that temperatures have been anomalously low on the Canadian side of the Arctic for quite a while now, or to be more precise: ever since the start of April, when the Arctic Oscillation that has been positive since the start of the year, became even more positive. It still hasn't let the Arctic out of its grip, which makes for vast cloudless regions over Greenland and the Canadian Archipelago. Great for clear satellite images, and obviously great for ultra-freezing temperatures.

I decided to go to the Daily Mean Composite page, compiled by the Physical Science Division of NOAA's Earth System Research Laboratory, that came in so handy when writing the End Zone series at the end of last year's melting season, and compare this year's April 1st - April 15th period with other years.This is the mean composite image for this year:

 This is how it looks like for other years (click for a larger image):

Flushing out the Fjord

I wrote a blog post on Jakobshavn Isbræ last year when a 7 square kilometer (2.7 square mile) section of the glacier broke up. Here's some basic information from Wikipedia on one of the most important Greenland glaciers, with an image of the glacier on August 5th last year (the glacier is on the bottom right, with the fjord in front of it filled with icebergs):

Jakobshavn Isbræ drains 6.5% of the Greenland ice sheet and produces around 10% of all Greenland icebergs. Some 35 billion tonnes of icebergs calve off and pass out of the fjord every year. Icebergs breaking from the glacier are often so large (up to a kilometer in height) that they are too tall to float down the fjord and lie stuck on the bottom of its shallower areas, sometimes for years, until they are broken up by the force of the glacier and icebergs further up the fjord.

Well, it appears that something convinced those icebergs to get a move on, because in just a few weeks time the Illulisat Isfjord has been flushed clean. On February 26th (day 57) resident Arctic expert Lodger informed us in Open Thread 6 that some of those icebergs had left the fjord. I didn't think much of it at the time (couldn't be bothered really, as images were too cloudy). On March 1st (day 60) everything seemed to be just hunky dory again, with gaps neatly frozen over, but apparently this was just a prelude to the Great Flushing.  I've made a reconstruction with a handful of satellite images that were clear enough to be used from day 52 (Feb. 21st) to day 102 (April12th). Check out the Royal Flush between days 82 and 83:

SIE 2011 update 4: slow, but steady

During the melting season I'm regularly writing updates on the current sea ice extent (SIE) as reported by IJIS (a joint effort of the International Arctic Research Center and the Japan Aerospace Exploration Agency) and compare it to the sea ice extents in the period 2005-2010. NSIDC has a good explanation of what sea ice extent is in their FAQ. I also look at other things like sea ice area, concentration, volume, temperature and weather forecasts, anything that can be of particular interest. Check out the Arctic sea ice graph webpage for daily updated graphs, maps and live webcam images.

April 13th 2011

Updates on SIE are few and far between, but there's no need to wear myself out with extensive analysis until the ice starts melting out for real, come May and June. In these first two weeks of April we saw the 2011 trend line completing the triple top, but the third top didn't match the first one either, and so the SIE maximum extent still stands. It will continue to do so as the 2011 extent numbers have continued to decline slowly, but steadily.

The 2011 trend line on the IJIS graph is still in the top of the lower group of trend lines that has been joined by a fiercely dropping 2004 trend line:

The current difference between 2011 and the other years is as follows:

• 2005: +164K(-26,297)
• 2006: +463K (-26,932)
• 2007: +317K (-27,521)
• 2008: -373K (-40,240)
• 2009: -244K (-26,781)
• 2010: -455K (-40,786)

Between brackets is the average daily extent rate for the month of April. 2011's average daily extent rate for April is currently -25,781 square km per day.

Over at Cryosphere Today the flatlining of the SIA (sea ice area) numbers around minus 1 million square km has basically come to an end, with the anomaly trend line going up and settling around the minus 700K mark:

First Forecasts 2: PIOMAS

Commenter Gas Glo has just reported that Jinlun Zhang of the University of Wachington's Polar Science Center has issued a first forecast for the September 2011 average sea ice extent: 5.0 million square kilometers.

As it says on Dr. Zhang's webpage: The ensemble forecasting system is based on a synthesis of a model, NCEP/NCAR reanalysis data, and satellite observations of ice concentration. The model is the Pan-Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS, Zhang and Rothrock, 2003).

Here's a nifty animation of the forecast:

To put this forecast of 5.0 million km2 into perspective, here are the NSIDC September SIE values for the past several years:

Trends in Arctic Sea Ice Volume

In an earlier post I proposed an asymmetrical S-shape called the Gompertz curve as a simplified, nonphysical model describing satellite-era trends in minimum sea ice extent (Figure 4). If future ice extent follows the same trend, this model predicts a September 2011 mean extent of 4.4 million km² (confidence interval 3.5–5.3), and extent falling below 1 million km², “virtually ice-free,” by 2024. I emphasize that extrapolating curves is a what-if exercise, not based upon physical understanding. Sometimes a statistical approach yields predictions fairly close to those obtained from more sophisticated physical models, but how well any prediction anticipates the real Arctic will be tested in the months and years ahead.

 

 Figure 4

 The observational data in Figure 4 show a gradual early decline in extent, recently steepening. Linear models do not capture this pattern. Quadratic models capture the recent steepening but do less well with the gradual earlier decline, and they imply an accelerating descent toward zero ice. Both quadratic and Gompertz are equally simple (3 parameters), but the Gompertz behaves differently at start and finish — a gradual early decline from some asymptotic initial level, and a more abrupt but also asymptotic approach toward zero at the end. This end behavior corresponds to the idea that late-summer remnants of sea ice, perhaps along coasts and fjords of the Canadian Archipelago and Greenland, could persist through some years after most central Arctic Ocean ice is gone.

Trends in Arctic Sea Ice Extent

 Proxy evidence suggests that the recent declines in Arctic sea ice extent and volume are unprecedented over at least the last few thousand years (Polyak et al. 2010). Historical records indicate that the seasonal ice zone, an area of northern seas that is ice covered in winter but not in late summer, has been expanding gradually since 1870, and more rapidly in the past three decades (Kinnard et al. 2008). Reinforcing that conclusion, combined submarine and satellite measurements show that ice has been thinning over much of the Arctic Ocean since the 1950s, so the remaining cover increasingly consists of thinner seasonal ice (Kwok & Rothrock 2009).

These longer-term studies place recent satellite-era change in perspective. Sea ice extent, in particular, has been relatively straightforward to define and measure by satellite. As a result, we have daily time series of extent and area going back into the 1970s, which confirm a recently accelerating decline. Decline has been most noticeable in late summer, but is visible across all times of the year. A cycle plot (Cox 2006) in Figure 1 illustrates changes in average extent and area (NSIDC data) broken down for each month, from November 1978 through March 2011.

Figure 1

Each squiggly line in Figure 1 tracks the mean sea ice extent (blue) or area (orange) for a particular month over roughly the years 1978 to 2011. The vertical axis shows the absolute ice cover in millions of km². Extent, for example, ranges from values near 16 million km² in winters of the earlier years, to 5 million km² or less in summers of recent years.

The declines visible in Figure 1 all are statistically significant. Figure 2 graphs the linear trends separately for each month.