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Arctic sea ice in retreat

Updated

A scientific brief as a web page: an abstract, numbered findings, three numbered figures and a method note, styled like a paper but live — every statistic below is computed in the browser from the 48 observations embedded in the page, and the figures answer to hover.

Brief · Cryosphere Data · NSIDC Sea Ice Index, 1979–2026 Unit · million km²

Abstract

Satellites have measured Arctic sea ice every day since 1979. The September extent — the summer low — has fallen by 0.74 million km² per decade, 11.6% per decade against the 1981–2010 average. The ten lowest Septembers on record all fall in 2007 or later. The winter maximum declines too, but four to five times more slowly in relative terms, so the ice that survives each summer is a shrinking share of each winter's cover.

Key findings

  1. The summer ice has lost a Kazakhstan. September extent averaged 7.31 million km² in 1979–1983 and 4.64 in 2022–2026: 2.7 million km² less, about the area of Kazakhstan.
  2. Every one of the ten lowest years is from 2007 on. The record, 3.57 million km² in 2012, has stood for fourteen summers.
  3. Winter recovers less each year. The March maximum falls 2.5% per decade, so the gap between winter and summer ice — what melts each year — has widened.

Figures

September extent and its trend

  • September extent
  • Trend, −0.74 M km² per decade
Figure 1. September mean Arctic sea ice extent, 1979–2026, with an ordinary least-squares fit. The shaded band is the 1981–2010 average ± one standard deviation.

The ten lowest Septembers

    Figure 2. The ten lowest September extents on record, ranked. Orange bars are years since 2016.

    Winter maximum and summer minimum

    • March maximum
    • September minimum
    Figure 3. Each year's seasonal range, from the March maximum to the September minimum. The top drifts down slowly; the bottom falls away twice as fast.

    Method

    Extent is the area of ocean with at least 15% ice cover, as monthly means for March and September from the NSIDC Sea Ice Index, version 3. The trend is an ordinary least-squares fit of extent on year over all 48 years; the percentage rate divides it by the 1981–2010 mean (6.41 million km² in September, 15.43 in March), the convention NSIDC uses. Year-to-year swings are weather: a single low year is not a trend, which is why the brief reports the fit and five-year averages.

    Data table
    Year September minimum March maximum Seasonal range

    How it's built

    • The numbers in the text are filled by the same script that draws the charts: each data-si span gets the slope, percentage or mean it computes, so prose and figures cannot disagree.
    • The ranked list is an ordered list whose bars are <i> elements sized by a --value custom property; no SVG at all.
    • The paper look — the abstract's label column, the leading-zero finding numbers — is CSS counters and a two-column grid that folds to one column on a phone.

    Source: National Snow and Ice Data Center, Sea Ice Index, as compiled by Our World in Data.

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