On 29 August 2022, a satellite-derived sea ice concentration product revealed the opening of the northern route of the Northwest Passage (NWP) through the Canadian Archipelago. Figure 1 illustrates the two NWP routes on a satellite image from 22 August last year (2021), when the northern route was not open. Figure 2 shows the ice concentration based on a satellite product that blends sea ice concentration from the Advanced Microwave Scanning Radiometer-2 (AMSR2) and the Visible Infrared Imaging Radiometer Suite (VIIRS). A false color RGB image using NOAA-20 VIIRS imagery at 19:40 UTC on the same day confirms the opening of the passage (Figure 3).

This is a notable occurrence, but not the first time it has been observed during the satellite era. The most recent year in which this route was open by this date was in 2011, and the last time this route was open was in September 2015. Figure 4 gives time series for both NWP routes from early spring through early winter for a number of years. As of late August this year, the northern route was well below the 1991-2020 average but above the 2011 record low. The ice area in the southern route was also below normal.

With continued trends and warming climate, this occurrence should become more common in the future. Why did the route open this year and why has it been closed at this time of the year for the past seven years? A better understanding of late spring/early summer surface and atmospheric conditions that are more conducive to opening of the passage would be extremely useful in preparing shipping for potential openings in the future.

Figure 1: Satellite image from 22 August 2021 showing the Northern and Southern routes through the Northwest Passage. (From the NASA Earth Observatory)
ScreenshotFigure 2: False color NOAA-20 VIIRS imager band RGB (bands 1 at 0.64 µm on blue), 2 at 0.865 µm on green), and 3 at 1.61 µm on red) at 19:40 UTC on 29 August 2022. Dark areas are open water with cyan being sea ice. The eastern portion of the northern route is relatively cloudy (gray).
ScrFigure 3: Blended VIIRS-AMSR2 sea ice concentration (0-100%).
Figure 4: Time series plots of sea ice area in the Northwest Passage from late April through late November for different years. Left: northern route; right: southern route. (Courtesy of Steve Howell, Environment and Climate Change Canada)

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