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• NEP navigation season for OW vessels lengthened to 92 ± 15 days in the 2010 s. • The 90-day SSA for OW vessels expanded by 35% during 1979 to 2018. • Trans-Arctic shipping routes became navigable earlier than the model projections. • Commercial ships could now transport 33–66% more goods from East Asia to Europe. • Aggressive actions should be taken to strengthen the Arctic environmental protect. Rapid declines in Arctic sea ice coverage over the past four decades have increased the commercial feasibility of trans -Arctic routes. However, the historical changes in navigability of trans -Arctic routes remain unclear, and projections by global circulation models (GCMs) contain large uncertainties since they cannot simulate long-term Arctic sea ice changes. In this study, we determined the changes in trans -Arctic routes from 1979 to 2019 by combining two harmonized high-quality daily sea ice products. We found that the trans -Arctic routes are becoming navigable much faster than projected by the GCMs. The navigation season for open water (OW) vessels along the Northeast Passage (NEP) has lengthened from occasionally navigable in the 1980 s to 92 ± 15 days in the 2010 s. In contrast, previous GCM projections have suggested that navigability would not be achieved until the mid-21st century. The 90-day safety shipping area for OW vessels expanded by 35% during 1979–2018, reaching 8.28 million km2 in 2018, indicating an increasing rate of 0.08 ± 0.01 million km2 per year. The shortest trans -Arctic routes were also shifted further north than the model projections. Regular ships have been able to safely travel north along the islands in the NEP and transit through the M'Clure Strait in the Canadian Arctic Archipelago during the 2010 s, while previous studies have projected that this would not be feasible until the mid-21st century. We also found that the improved navigability of trans -Arctic routes enables commercial ships to transport approximately 33–66% (at the same load factor) more goods from East Asia to Europe during the Arctic shipping season than by the traditional Suez Canal route. These findings highlight the need for aggressive actions to develop mandatory rules that promote navigation safety and strengthen environmental protection in the Arctic. [ABSTRACT FROM AUTHOR]