Intense storms increase global ice area.

Abstract

Earth's energy balance is strongly modulated by sea ice cover. Cyclones can impact sea ice extent by amplifying wave activity, promoting ice breakup, advecting heat and moisture, and enhancing sea ice drift. Due to the range of processes involved, the net effect of cyclones on global ice area has yet to be quantified. Here we analyze two decades of intense cyclones that interact with the global marginal ice zone, showing that storms enhance the seasonal ice growth and decay cycle in both hemispheres. Cyclones intensify equatorward winds and ice advection within a cooling ocean during the cold season and enhance poleward motion within a warming ocean during the warm season. Collectively, cyclones increase global annual mean ice area by 13%, an effect that has increased in recent years. Southern hemisphere cyclones have the strongest influence on global ice area, with autumn and early winter cyclones strongly expanding ice area. While these increases are partially offset by ice losses in early austral summer, the low overall Antarctic sea ice extent in late summer limits further losses, leading to an asymmetric annual cycle where intense cyclones enhance global ice area from April through October but only destroy it in November and December.