Annual means account for 68% of the sample Antarctic sector covariance rise in a 1989–2024 calendar-year split

We test the timescale of a reported rise in shared Antarctic sea ice extent variation. We use five Sea Ice Index Version 4 sectors. The comparison has 27 years in 1989–2015 and nine years in 2016–2024. We remove each period's calendar-month means. An exact covariance split separates annual means from departures within each year. Summed cross-sector covariance rises by 0.1897 (million square kilometres) squared. Annual means account for 68.1% of this sample rise. The within-year part rises by 0.0606, with a 95% two-year block interval of -0.0107 to 0.1310. All three covariance change intervals include zero. Its variance ratio stays below one, at 0.915. A July-to-June split gives a different budget. These data do not establish a change at all timescales or identify a physical cause. The fraction is a sample budget, with large uncertainty in its parts. Nine recent years, the year boundary, one extent product, and the block assumptions limit inference. The package gives code, derived inputs, uncertainty draws, source hashes, and an independent numerical audit.

Antarctic sea ice · regional covariance · time aggregation · annual means · within-year variation · uncertainty