Possible influences of the El Niño/Southern Oscillation (ENSO) on winter shipping in the North Pacific (NP) are investigated using marine observations contained in the International Comprehensive Ocean-Atmosphere Data Set (ICOADS). Shipping frequency is interpreted using the number of ship reports accumulated in each 2° × 2° box-space throughout the winter season. Analyses reveal that shipping across the NP follows major "great circle" routes from the South China Sea (SCS) along the coasts of East Asia and Japan before heading eastward along the open ocean north of the Aleutian Islands toward the western coasts of North America. The above routes are shorter in navigational distance and avoid strong winds and high waves in the regions south of the Aleutian Islands caused by the Aleutian low.

In the far north NP, total shipping frequency exhibits evident interdecadal variability. El Niño tends to weaken ocean waves in these regions. Better maritime conditions facilitate shipping efficiency and result in decreases in navigation times and the number of ship reports, yielding a negative correlation between interannual components of Niño-3.4 SST and shipping frequency. In the Philippine Sea and the northern SCS, total shipping frequency also exhibits clear interdecadal variability. El Niño tends to weaken prevailing northeasterly flows and trade winds, leading to weakened ocean waves and decreased navigation times and ship-report numbers. Interannual components of Niño-3.4 SST and shipping frequency are negatively correlated. Overall, ENSO’s influences on winter shipping in the western and northern NP are indiscernible in the aspect of total shipping frequency, but are notable in the interannual-variability aspect of shipping.