Sea ice choke points reduce the length of the shipping season in the Northwest Passage

Arctic sea ice has shifted from a perennial (older, thicker ice) to a seasonal (younger, thinner) ice regime, leading to the increasingly common belief that shipping through Canada’s Northwest Passage is becoming more viable. Here, we use the Risk Index Outcome values derived from the Polar Operational Limit Assessment Risk Indexing System and analyze recent changes to shipping season lengths along individual sections of the Northwest Passage routes from 2007 to 2021. Results show that multi-year ice flushed southward from high-latitude regions maintains the so-called choke points along certain route sections, reducing overall shipping season length. There is considerable spatiotemporal variability in shipping season lengths along the southern and northern routes. Specifically, parts of the northern route exhibit a decrease of up to 14 weeks over the 15 years. The variability of shipping season and, in particular, the shortening of the season will impact not only international shipping ..., , , # Data from: Sea ice choke points reduce the length of the shipping season in the Northwest Passage

[https://doi.org/10.5061/dryad.p5hqbzkx8](https://doi.org/10.5061/dryad.p5hqbzkx8)

These files are the data we generated, analysed, and used resulting in the figures in the Nature Communications Earth & Environment manuscript associated with these files. The datasets contain shipping season lengths in weeks (2007-2021) at 10 km intervals along the four Northwest Passage shipping routes (route locations are shown in the manuscript Figure 2a).

The values were derived from weekly Canadian Ice Charts that we converted to Risk Index Outcome (RIO) values using The International Maritime Organization’s Polar Operational Limit Assessment Risk Indexing System (POLARIS), and derived annual shipping season lengths in weeks where RIO >=0, for ships across a range of different ice strengths.

The files are spreadsheets of shipping season lengths along the four shipping routes: NWP-S, NWP-N1,...