Asymmetric response of Arctic sea ice and navigation to carbon emissions

Arctic navigability has far-reaching socioeconomic consequences, but how the navigation will respond to negative carbon emissions proposed to mitigate global warming remains unclear. Based on the idealized CO 2 ramp-up (284.7–1138.8) × 10 –6 and symmetric ramp-down (1138.8–284.7) × 10 –6 simulations, we demonstrate asymmetric responses of sea ice conditions to the symmetric CO 2 forcing. At the same CO 2 level, Arctic sea ice extent and thickness in the ramp-down period reduce by 8.1%–27.2% and 18.6%–27.9% relative to the ramp-up period, respectively. Consequently, the navigable area and season show an additional increase (by 16%–32% and 1 mon, respectively) when the CO 2 returns to the initial level. This contributes to a northward migration in the optimal shipping routes, with shortened voyage along the Northern Sea Route (–4.0% [–16.6%, 15.0%]) and Northwest Passage (–2.7% [–10.3%, 8.5%]). Despite using the idealized carbon dioxide remove scenario, our results highlight the asymmetric response of Arctic sea ice and navigation to carbon emissions and may serve as an important addition to the assessment of the effect of potential carbon removal in future.