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.
May 15th 2011
First, let me apologize for not doing an update last week, even though I promised I would do one every week from now on. There's only so much time, and the pieces on sea ice thickness took precedence. And although as fascinating as always, nothing really spectacular has been happening with the Arctic sea ice in the past few weeks. But this depends on your perspective of course, as there's always more to the eye in the Arctic.
What could be labeled as a lack of spectacle is the fact that the sea ice extent decrease has been incredibly steady. Except for a very short blip upwards when an extent increase of 26,094 square km was reported for May 6th, the trend line for 2011 is dropping very gradually (as can be seen on the IJIS graph below). The curve has been remarkably steady all year.
However, and this in a way is quite spectacular, the actual circumstances on the ground haven't been steady at all. The Arctic Oscillation turned negative at the start of the month and as we saw in the previous SIE update this meant that the anomalously warm air in Siberia was moving slowly towards North America. But instead of getting more negative the AO index has remained stuck just below neutral.
High and low pressure areas are continuously trading places, resulting in ice displacement arrows pointing every which way from one day to the next. One other effect is that in the past week temperatures have shown a negative anomaly practically all over the Arctic (more on that below). Moreover, our CAPIE index has dipped several percentage points below other years, which could be a sign that there is a slight divergence of ice (more on that below as well).
Both these factors, especially combined, ought to have slowed down the rate of extent decrease. But extent is plodding downwards unperturbed, and showing a very decent average daily decrease for the month so far. So the fact that extent decrease isn't spectacular, is pretty spectacular, si vous catchez mon drift.
Sea ice extent (SIE)
Here's the IJIS SIE graph with its smooth curve for 2011. It has just passed the 12 million mark:
The current difference between 2011 and the other years is as follows:
- 2005: -135(-44,778)
- 2006: +209K (-43,432)
- 2007: +9K (-41,991)
- 2008: -291K (-45,373)
- 2009: -478K (-53,952)
- 2010: -179K (-67,661)
Between brackets is the average daily extent rate for the month of May. 2011's average daily extent rate for May is -51,049 square km, which is quite a bit more than most other years, very close to 2009, but of course out of 2010's league. 2010 has been catching up very fast - the difference with this year was 474K two weeks ago - and is now in 5th spot. It will take the lead quite soon and hold it until the end of June, with the incredible streak we witnessed last year. 2011 is currently in third position, more or less tied with 2007.
The slowly, but steadily increasing rate of decrease for this year is also reflected in this graph from the university of Bremen that shows the change per month of Arctic SIE:
If things continue in this manner, 2011 will soon have the fastest rate of SIE decrease after 2010.
The trend line on the Cryosphere Today SIA anomaly graph has been hovering again around the minus 1 million square km mark in the past two weeks:
Because of a combination of ice pushing back towards the Siberian coast and even some refreezing due to anomalously temperatures, the SIA decrease was halted in the East Siberian Sea, Kara Sea and Laptev Sea. The SIA in the Barentsz Sea hasn't stopped from going down though, and things in the Bering Sea are still progressing very fast, as noted in this blog post. It will have melted out before the end of the month, which means the Chukchi Sea will come into play. The Beaufort Sea SIA number is bound to go down any day now. Hudson Bay and Baffin/Newfoundland Bay have continued to go down as well, and my expectation is that they will melt out very fast.
All in all SIA numbers have been going down a bit faster than SIE numbers, and this means that the percentage on our CAPIE index has gone down a tad as well. Because of the freeze-up during winter and the uniform shape of the ice pack (meaning no holes), area and extent are very similar, despite the fact that they are calculated differently. This is why the CAPIE percentage hovers around 95% until the second half of May, when percentages start to drop, because of the ice breaking up at the fringes.
In this respect 2011 is a bit early when compared to other years in the 2006-2011 period:
1) melt ponds on the ice fooling the satellite sensors into reporting more open water than is actually there (which has a greater effect on calculations of sea ice area, and thus a dropping percentage).
2) convergence or divergence of the ice floes. If they converge, the percentage goes up, because there is less open water between them and the ice pack becomes more compact (making the difference between SIA and SIE smaller). Conversely, if they diverge, the CAPIE ratio goes down.
Well, 1) can't be in play right now, because the air is way too cold for melt ponds to form. And thus it has to be 2), in other words, an early divergence of the ice pack, which nevertheless didn't have much of an effect on the steadily declining SIA and SIE numbers, as noted in the introduction.
For over a week now much of the Arctic is anomalously cold, as can be seen on this NOAA/ESRL temperature anomaly map:
All the world's heat seems to be in the Antarctic, and except for a mildly warm Beaufort Sea and a neutral Greenland (which had been extremely cold the past 1-2 months) all of the Arctic is between 5 to 10 degrees below normal.
I have managed to remind myself to save most of the images from the DMI temperature map (updated twice a day) and can now give an impression of what has happened in the past two weeks:
We can see how the greens have slowly taken over the very cold Canadian Archipelago and how the yellows and oranges are pushing in from the south on both the Atlantic and Pacific side of the Arctic. But apparently this is slower than normal, and a light bluish hue continues to pop up here and there.
The relative cold is expressed more clearly in the DMI temperature above 80N graph:
It's difficult to forecast what is going to happen next. The AO is forecasted to remain slightly negative, which could mean much of the same, or perhaps even a slowdown in SIE and SIA decrease. A shift in weather conditions could mean the opposite, especially if they remain more constant than they are now.
But recent developments are evidence that the ice on the fringes is very weak. Air temperatures are down all over the place and ice displacement is geared more towards divergence than convergence. This can only be compensated by the fact that ice floes on the fringes (especially on the Siberian side of the Arctic) is relatively thin.
We'll just have to wait and see what happens. The 12 million mark has been passed, moving to 11 million now.
TIPS - Other blog posts and news articles concerning the Arctic and its ice:
Patrick Lockerby has released his first update for Arctic Ice May 2011.
The Montreal Gazette: 'Unprecedented' 1999 Arctic storm called portent of future