Regime Shift in Arctic Ocean Sea‐Ice Extent

Abstract A regime shift is an abrupt, substantial, and persistent change in the state of a system. We show that a regime shift in the September Arctic sea‐ice extent (SIE) occurred in 2007. Before 2007, September SIE was declining approximately linearly. In September 2007, SIE had its largest year‐to‐year drop in the entire 46‐year satellite record (1979–2024). Since 2007, September SIE has fluctuated but exhibits no long‐term trend. The regime shift in 2007 was caused by significant export and melt of older and thicker sea ice over the previous 2–3 years, as documented in other studies. We test alternatives to the traditional linear model of declining September SIE, and discuss possible explanations for the lack of a trend since 2007.