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Cryosphere · Arctic sea ice

The Arctic is melting in slow motion.

Since November 1978, microwave satellites have watched the ice cap of the Arctic Ocean grow every winter and retreat every summer. Forty-six years of monthly data are scrubbed into this map. Pull the year slider — and watch a familiar shape become unfamiliar. The floes drifting on top are real currents made visible: the Beaufort Gyre rotates clockwise west of Alaska, the Transpolar Drift carries Siberian ice across the pole and out through the Fram Strait.

Sea ice extent
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M km²
Sea ice volume
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k km³
How the visualisation works

Monthly ice extent values come directly from NSIDC Sea Ice Index v4 (Fetterer et al., 568 monthly values 1978-today). Monthly ice volume comes from PIOMAS (Polar Science Center, University of Washington). The shape of the ice cap is a procedural climatological model — for each month we use known mean ice-edge positions per longitudinal sector and scale them so the rendered area matches the real NSIDC value for the year and month you have selected. The drifting floes are synthetic shapes following a parametric Beaufort Gyre and Transpolar Drift — they melt when they cross the current ice edge. The map is a polar stereographic projection centred on the North Pole, showing everything north of 50°N.

What the data shows

Four readings of the same time series.

  1. How we see the ice.

    Sea ice emits and reflects microwaves differently from open water. The Scanning Multichannel Microwave Radiometer on Nimbus-7 began the record in November 1978, succeeded by the SSM/I and SSMIS sensors. Daily 25-kilometre grids cover the entire Arctic regardless of darkness or cloud — the only kind of measurement that could survive the polar night and the long winter cloud cover.

  2. Seasonal cycle versus long-term loss.

    Sea ice grows from November to March, melts from April to September. The seasonal swing is roughly nine million square kilometres — about the area of the United States plus India. Layered over that swing is a steady downward trend: September minimum extent has fallen by about 13% per decade since 1979 (Stroeve & Notz 2018). March maximum has fallen too, by about 2.7% per decade. The September 2012 record minimum, 3.41 million km², stands as the lowest single measurement in the satellite era.

  3. Volume falls faster than area.

    PIOMAS reanalysis combines ice thickness, drift and observation into an ice-volume estimate (Schweiger et al. 2011). The volume picture is far more dramatic than the area picture: between 1979 and today, September ice extent has fallen by about 40%, but September ice volume has fallen by roughly 75%. The Arctic is not just smaller; what remains is thin. Multi-year ice — the thick old floes that used to cover most of the basin — has dropped from about 60% to around 5% of the cap (Comiso 2012).

  4. Drift and the albedo trap.

    Two patterns dominate Arctic ice motion. The Beaufort Gyre spins clockwise north of Alaska, retaining ice for years. The Transpolar Drift carries ice from the Siberian shelves across the pole to the Fram Strait between Greenland and Svalbard, where roughly 10% of the Arctic cap is exported into the North Atlantic and lost every year (Rampal et al. 2009). Ice reflects 80% of sunlight; open water absorbs more than 90%. Every square kilometre of summer ice lost lets the ocean drink in heat that used to bounce back to space — Arctic Amplification in one sentence, and the reason the polar region is warming three to four times faster than the global average.

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