Figure 1. A global view of shipping in the Arctic.

Monthly average (A) number and (B) density of ships (units: number of vessels per square kilometer) present in the Arctic Ocean at different longitudes and (C) the main shipping routes in the Arctic in 2014. The number of ships in (A) represents the number of ships at any latitude >66.4^oN for 1/4 degree longitude sectors around the Arctic Circle, and the colors denote the type of ship. (B) Heat map displaying the average number of ships per square kilometer and month during 2014 in a 1/4 × 1/4 degree cell grid. The increase in density toward the North Pole is due to the decrease of the area covered by each grid cell with increasing latitude while observing the same number of ships. Ice cover in September 1014 is represented in white. (C) Main navigation routes in the Arctic (in red) obtained by identifying the two most densely grid cells per month on average for each 1/4 degree longitude bands (see Methods), The monthly average density from (B) is also shown in grey scale (ice is not shown). Figure generated with python 3.x (https://www.python.org/) and PyShp (https://pypi.python.org/pypi/pyshp).