Arctic Shipping Guidance from the CMIP6 Ensemble on Operational and Infrastructural Timescales

The expectation of a seasonally ice-free Arctic expected by mid-century has sparked economic and geopolitical interest in potential Arctic opportunities and risks. But substantial sea ice variability across timescales suggests an uncertain future for forecasts of marine accessibility, especially over operational (< 2 years) and infrastructural (> 5 years) time spans that significantly influence decision-makers planning ship routing, emergency management, port investment, and more. Here, we use three marine accessibility schemes applied to CMIP6 scenarios to quantify Arctic shipping season variability and uncertainty across these decision-relevant timescales. We compare route projections across climate models and accessibility schemes to show that the choice of methodology significantly affects information important for decision-making. We find high variability and uncertainty in voyage time notably in the critical "shoulder" seasons on both timescales. This leads to increased risk over the next several decades, with high short-term uncertainty particularly at the end of the shipping season for the next 25 years. Navigation risk is expected to decline from 2045 onward. Knowledge that accounts for sea ice variability, simulation quality, and accessibility algorithm allows for better investment decisions and the minimization of unforeseen costs due to delayed and canceled voyages. Here we develop and demonstrate a framework for developing more timely and salient information to guide decisions on Arctic shipping relevant to both operational and infrastructural horizons as climate projections become spatially and physically better resolved.