Old Ice and the Northwest Passage

Even if the Arctic continues to warm, a Northwest Passage sea route is not a done deal.

This animation from the National Snow and Ice Data Center shows the distribution of one-year and multi-year ice by season from 1981 to 2007.  The oldest ice is red.  Look at the way the winds and currents grind it against the islands of Northern Canada, year after year. 

Katherine Wilson and her co-authors note that if Arctic warming continues, and the one-year ice within the straits between Canada's islands melts, the older ice could work its way in towards the Northwest Passage.  That multi-year ice can be deadly for shipping: Shipping in the Canadian Arctic.  Other Possible Climate Change Scnearios.  This could limit the future capacity of the Passage, or increase transit costs.

The islands facing the Arctic Ocean, and the first year ice in the straits between, create a barrier protecting the Northwest Passage from muli-year ice:

The region to the north of the NWP [their shorthand for the Northwest Passage - Ben], the Queen Elizabeth Islands (QEI), [in the map above, working to the upper left from Greenland, are Ellesmere Island, the rest of the Queen Elizabeth Islands, and - the last large island before the mainland - Banks Island - Ben] acts as a barrier between the Arctic Ocean and the NWP. Sea ice within the Arctic Ocean circulates in an anticyclonic gyre maintaining high ice pressure and shear along the northwest perimeter of the QEI and thereby creating the thickest and most heavily ridged sea ice in the world.... Old ice (OI) from the Arctic Ocean drifts into the QEI from the west, blocking the narrow passages between islands. Ice concentrations in the QEI are extremely high resulting in limited and incomplete navigation and scientific study....

Arctic warming may increase opportunities for old ice intrusion into the Passage:

The conventional wisdom based on GCM [the five global climate models in the Arctic Climate Impact Assessment - Ben] predictions is that with climate change the navigation season will lengthen with lighter ice conditions due to earlier break up and later freeze up. Both Melling and Falkingham feel that warmer temperatures, whether atmospheric or oceanic in origin are melting greater amounts of FYI [first year ice - Ben] in the QEI. FYI controls the supply of the OI from the Arctic Ocean to the NWP and a reduction will allow more OI from the Arctic Ocean to enter the Archipelago in greater quantities. Thus, it may be more likely that there will be only a minor lengthening of the season as OI drifts into the QEI to fill in the open water gaps....

Creating a hazard to shipping:

An increased incidence of warm summers anticipated with climate warming may cause a reduction in FY fast ice permitting old ice to drift into the NWP, thereby increasing the rate of, supply to and thickness of ice within the NWP. OI is extremely strong and dangerous to all ships, even icebreakers, and the increase of this ice in the NWP will result in increased hazards to the marine environment and its users....

Winds and ocean currents can drive sea ice against coastlines and into narrow channels, creating high-pressure zones capable of crushing ships and creating barriers to navigational pathways....

Depending on how things go, this could be permanent, or just a transitional factor:

Increased drifting OI creating choke points may be a fact in future navigation in the NWP, or it could be the kind of navigation to expect in the interim as the ice free summers predicted by GCM’s are reached....