How the Arctic lost nearly half its summer sea ice in less than 50 years
Satellite monitoring of Arctic sea ice begins. In September — the annual minimum — ice covers roughly 7 million km² of ocean. The frozen canopy stretches from Canada to Siberia, a vast white shield reflecting sunlight back into space.
A decade of warming has begun to show. The ice edge has pulled back noticeably from its 1979 extent. Scientists start to document a downward trend that will only accelerate. The Arctic is warming twice as fast as the global average.
By the turn of the millennium, the pattern is unmistakable. Summer ice extent has dropped by roughly 1 million km² — an area larger than France and Germany combined. Multi-year ice, the thick old ice that once dominated the Arctic, is thinning.
The Arctic of 2010 is unrecognisable from 1979. Ice extent has fallen to around 4.9 million km². Shipping routes through the Northwest Passage open for weeks at a time. The feedback loop intensifies: less ice means more dark ocean absorbing heat, accelerating further melting.
The September minimum has shrunk to roughly 4.3 million km² — a loss of nearly 40% since records began. Scientists warn that ice-free Arctic summers could arrive within a decade. What took millennia to form is vanishing in a human lifetime.
Source: NSIDC Sea Ice Index v4.0 · September monthly extent