Albedo Weekly

Climate indicators · NSIDC, Sea Ice Index v4

Arctic sea ice in September

4.81 million km²

September 2026, monthly mean extent. September 1979: 7.05 million km². Trend since then: -0.74 million km² per decade.

2.04.06.08.010.019791991200220142026
Arctic sea ice extent in September, million km², NSIDC Sea Ice Index v4.

What it measures

The area of ocean covered by at least 15 percent ice in September, when the Arctic ice reaches its yearly minimum, measured by satellites.

Why it matters

Bright ice reflects sunlight back to space; dark water absorbs it. That reflectivity is called albedo, and it is why less ice means more warming.

Source and method

NSIDC, Sea Ice Index v4. Monthly mean extent for September as published; the trend is a straight-line fit through all years.