Correction statement with links to details here.
It's bad form to blog on consecutive nights, but I'm now going to say something that has been on my mind for over a week.
Last year, and the year before, I recollect a lot of excitable discussion at the forum in June about how we were going to see a crash in sea ice. A lot of talk about how the weather would shift and massive losses would start, of course as we now know, that just didn't happen.
This year I'm seeing the same sort of discussions over at the forum, but I am more persuaded by hard numbers than qualitative arguments. I am by nature conservative so I am not going to change my opinion now, I'm going to wait until I can look back at June in its entirety. But there is one strand of evidence that has me suspecting we might be in for a crash of the same order as 2012.
In my previous post I showed how compactness has finally started dropping. But the same thing happened this time in 2013, and look where that summer took us. Drops in compactness tell us nothing about the coming melt season at this point in June, because absent other information they can go either way, drops can be followed by periods where compactness ceases to drop as much. Extent anomaly remains rather level, while area anomaly falls, such a situation is not exceptional for June.
It is only the US Navy's HYCOM-CICE model that is getting me quietly excited about the possibility of this year seeing a crash like 2012 and I don't just mean in terms of area or extent, I mean in terms of the pivotal impact of a storm.
I posted a few days ago, closing with this image.
The region indicated, from Laptev to Chukchi being my 'watch this space' region for the 2015 season. Now here is what the model is showing for the recent past and up to this time next week.
On around the 10 June a massive storm came from Barents over the pack towards Chukchi, discussed as a future point of interest in Neven's blog on 4 June 2015. This is shown in GFS, here shown on 10 June 2015 from Wetterzentrale.
That plot shows geopotential height in colours and sea level pressure in isobar contour lines. In the HYCOM model the impact of this was, as seen above, massive. Indeed it was far more massive than I had expected at the time.
Is there any reasonable expectation that what HYCOM predicts could be real? Below I show HYCOM for 18 June 2015 as predicted on 10 June 2015 and the actual for 18 June 2015.
Considering that the upper image is for predicted weather and the lower image is for the model run using actual weather, the similarities are close. But this is just for one day (and the other days I have checked are for a few more days), furthermore this doesn't rule out weather over the coming week changing from what is forecast. However consider the ice state shown for 25 June 2015, this is the worst state for the middle of June that I can recall seeing for any index.
For the sake of argument, let's accept this as a true picture of ice state next week. This state is under peak seasonal insolation, and suggests a lot of dispersed ice in the upper left quarter of that plot. It is not unreasonable to consider that almost everything under 2m thick will be gone by this September as ice/ocean albedo feedback works on the ice. That could leave a similar extent of ice as in 2012, possibly less.
It might be supposed that this would support claims of snow cover driving the ice loss in summer. One problem with that is that in 4 June 2014 ice thickness was similar to 4 June 2015.
The other problem is that the swath of thin ice started with the storm around 10 June and clearly evolved from the immediate impact of that storm. The proponents of the idea that snow cover will drive this season will have to await another year to test their theory. That's not a problem, if the theory is right, it will be successful again under better test conditions in another year.
HYCOM may not be correct. If that is the case we will know by the end of this month, the massive thinning and dispersion predicted for 25 June will be clear by the 30 June as highly abnormal concentration in the sea ice maps, and will result in strong decline in compactness across Chukchi, East Siberia Sea, and the Laptev Sea, it will likely be clearly abnormal in MODIS. At present, in my opinion the case for such corroborative evidence is not made.
An Anonymous commenter has raised the issue of a disagreement between the two HYCOM versions, HYCOM-Arctic & HYCOM-Global. In the above I used HYCOM-Global, here is an update with HYCOM Arctic.
If HYCOM is correct then the ice state this year is far worse than 2012 across the entire Siberian Coast, and as 2012 was the last major crash it remains reasonable to ask if 2015 will see similarly low sea ice by September. However HYCOM Arctic is significantly thicker than HYCOM Global. But as it is only 22 June it is too early to tell from the sea ice concentration data if this is a real state, we should know by the end of this month.
Anyone thinking about accusing me of bias in selecting the thinnest model should read my posts on the Slow Transition. ;)