The melting sea ice in the Canadian Arctic is now a hindrance, not a help, to shipping.

Shipping companies had hoped that melting sea ice would open up shorter shipping routes through the Canadian Arctic, but thicker ice moving in from further north may dash those hopes.

“North [of the Northwest Passage] “No new routes are expected to open anytime soon.” Allison Cook At the Scottish Association for Marine Science.

For over a century, sailors have navigated the icy waters of the Canadian Arctic along the Northwest Passage, a dangerous but efficient sea route connecting the Atlantic and Pacific oceans. As climate change melts the sea ice, the southern part of the passage is less dangerous, and since 1990, voyages through the Northwest Passage have quadrupled.

The North Strait is expected to be an even shorter route, but it is ice-bound for longer periods than the South Strait, and so fewer ships use it. But because the entire route was almost ice-free in the summer of 2007, and the climate has continued to warm since then, many believe the North Strait route will soon become regularly navigable. This possibility has spurred ideas of a boom in Northern Sea Routes.

Cook and his colleagues assessed whether this vision was working using ice charts provided by the Canadian government to ship captains between 2007 and 2021. For each leg of the Northwest Passage, they calculated the number of weeks per year when ice was light enough for moderately ice-hardened ships to navigate safely.

The detailed images of the ice reveal that rather than the passage opening, the safe passage window shortened at several “choke points” along the route, particularly along the northern route. For example, the passage window in the eastern Beaufort Sea shortened from 27 weeks to 13 weeks. The passage window in McClure Strait shortened from 6.5 weeks per year to just two weeks. In other areas, passage windows increased by a few weeks or remained unchanged, but the passage window that determines the overall passage window is determined by the shortest passage window, Cook said.

Researchers believe the shortened season is primarily due to an increase in thicker sea ice flowing in from an area known as the “last ice field” north of Greenland, which is expected to become the last remaining bastion of sea ice in the Arctic Ocean as the climate warms. “Climate change is making the sea ice a little less intense and a little more mobile,” Cook says.

The findings are consistent with expectations that ice will remain in the Canadian Arctic the longest, he said. Amanda Lynch The bigger geopolitical and economic question now is how the melting ice will affect shipping on the Russian side of the Arctic, said Robert G. Schneider, a researcher at Brown University in Rhode Island who was not involved in the study.