While the drivers of historical decadal variability are known with medium confidence, there is currently limited evidence and low agreement concerning causes of the strong recent decrease (2016)(2017)(2018), and low confidence in the ability of current-generation climate models to reproduce and explain the observations. {3.2.1.1} Shipping activity during the Arctic summer increased over the past two decades in regions for which there is information, concurrent with reductions in sea ice extent (high confidence). Transit times across the Northern Sea Route have shortened due to lighter ice conditions, and while long-term, pan-Arctic datasets are incomplete, the distance travelled by ships in Arctic Canada nearly tripled during 1990-2015 (high confidence). Greater levels of Arctic ship-based transportation and tourism have socioeconomic and political implications for global trade, northern nations, and economies linked to traditional shipping corridors; they will also exacerbate region specific risks for marine ecosystems and coastal communities if further action to develop and adequately implement regulations does not keep pace with increased shipping (high confidence).