The season of contrasts continues. The conclusion after the freezing season that the ice on the Atlantic/Siberian side of the Arctic looked vulnerable and the ice on the Pacific/Canadian-Alaskan side of the Arctic should be thicker than usual, is extending itself into the melting season: Whereas the Northern Sea Route could be opening up in record time, the fast ice in the Northwest Passage has still to start breaking up.
We now have four seasons of wonderful satellite images provided to us by the LANCE-MODIS data system, and so we have an animation that allows us to compare this year's situation with that of previous years:
Even though yesterday's image (day 164) is 4-5 days behind the other years, it's as clear as day that this year the NWP is very slow to open up. One partial explanation for the discrepancy with other years so far is air temperature. Take for instance the temperature anomalies for the first three months of the year (source: NOAA daily mean composite page):
2010 was hottest and thus broke up/melted out fastest, followed by 2011. Temps in the NWP in 2009 were mostly non-anomalous, except for Lancaster Sound, where the ice already had begun to break up by now. The first three months of this year temps all over the NWP were non-anomalous, which means it was as cold as the 1981-2010 base period on average. In other words, it was pretty cold and this is probably the main reason the ice is still holding out.
With this info in mind, the big question of course is whether the NWP will become navigable this melting season, as it was in 2007, 2008, 2010 and 2011. This depends on many factors, the most important of which will be weather conditions. But another factor that is not to be underestimated is the amount of multi-year ice in the NWP. The latest SEARCH Sea Ice Outlook has some info on that in the June 2012 Regional Outlook report (hat-tip to Diablobanquisa, who published a blog post on the NWP yesterday):
Figure 1 shows the concentration of multi-year ice (MYI) in the western channel of the Northwest Passage at the end of May this year and for the past four years compared to the 1981-2010 climatology. Howell points out that concentration of MYI in the region is well below the historical average and that it is likely the seasonal first-year ice will clear during the melt season. However, clearing may only be temporary since a large open water area provides a pathway for MYI to transit south from the Queen Elizabeth Islands. The ensemble prediction from the PIOMAS model submitted by Zhang and Lindsay is in agreement and shows a mostly open Northwest Passage (Figure 2a). There is significant uncertainty in both forecasts. Zhang points out that the standard deviation in the model ensemble is high in this area (Figure 2b) and Howell notes that predicting clearing in advance of breakup is difficult due do a number of factors that have to occur in tandem during the melt season.
Figure 1. Spatial distribution of multi-year ice concentration (in tenths) within the Western Parry Channel region of the Northwest Passage at the end of May. The median climatology 1981-2010 is compared with 2007, 2009, 2010, 2011, and 2012. Data is from the Canadian Ice Service (Howell).
Figure 2. (a) Ensemble prediction of September 2012 sea ice thickness in the Northwest Passage region and (b) ensemble standard deviation (SD) (Zhang and Lindsay).
So there's a lot of first-year ice in the NWP this year, more than ever, but the relatively low temperatures during most of the freezing season have probably thickened that FYI up more than in previous years.
With regards to the "large open water area provides a pathway for MYI to transit south from the Queen Elizabeth Islands": it didn't happen in 2010 and 2011, despite a substantial inflow of multi-year ice from the Arctic Basin (see for instance these animations from 2010). Somehow that MYI didn't make it all the way to the NWP, probably because of in-situ melting and transport cut short by the onset of the freezing season. Which is why the MYI concentration shown in figure 1 is so low this year. In principle, yes, transport of MYI from the Arctic Basin should block the NWP, but I haven't seen it yet.
And so it all depends on the weather and the thickness of this first-year ice in the NWP. It was cold there for most of the freezing season, so it's most probably thicker than in previous years, but whether it will be enough to keep the NWP from opening up, remains to be seen. We'll know more in a couple of weeks.