Improved CMIP6 Projections of Hudson Bay Navigability Using Bias Correction and Route Continuity

Abstract. Hudson Bay’s seasonal sea ice limits maritime access to the Port of Churchill. This study improves on past efforts to project future navigability of shipping routes from Churchill by correcting for substantial model biases, better combining  SIC and SIT into calculations, and incorporating a novel path-finding approach that requires continuous navigable routes (rather than relying on spatial domain averages). We evaluate future navigability for Type E vessels under two criteria: ice-free and low-risk (applying the Polar Operational Limit Assessment Risk Indexing System (POLARIS)). Additionally, we examine both the global shipping route (Churchill–Labrador Sea) and regional connectivity within northwestern Hudson Bay (Churchill–Chesterfield Inlet). In the 1980s, median navigable periods (NPs) for the Churchill–Labrador route were 102 days (ice-free) and 123 days (low-risk), compared to 106 and 123 days, respectively, for the Churchill–Chesterfield route. By the 2010s, these periods increased by approximately 4 weeks. Various methods of employing POLARIS and climate models yield a range of baseline NPs but consistent trends. Each additional 0.5 °C of global warming extends NPs by 13–18 days up to 3.5 °C, beyond which the rate of increase accelerates. Under 5 °C warming (late 21st century in SSP5-8.5), the Churchill-Labrador Sea route would remain ice-free for up to 265 days (8.8 months), representing and increases of 137 days relative to present conditions. Under low-risk conditions, navigability would reach 304 days (10.1 months). This demonstrates that year-round shipping would require ice-strengthened vessels throughout the 21st century even with a high-end warming scenario.