気候変動：南極の海氷減少が嵐の発生を促す

Recent record lows in Antarctic sea-ice extent have led to increases in the frequency of storms over the newly ice-free ocean, reports a paper published in Nature this week. In 2023, the concentration of sea ice in the oceans surrounding Antarctica fell by as much as 80% in some areas, leading to increased heat transfer from the ocean to the atmosphere, which is associated with increased storminess. The findings reveal the wider climate system impacts of sea-ice loss.

The reduction of sea ice in Antarctica can lead to ocean warming, a weakening of the carbon sink in the Southern Ocean and population reductions in penguin colonies. While researchers have observed a large-scale reduction in sea ice beginning in 2016, 2023 set a record low sea-ice concentration beginning in February, with 2.33 million square kilometres of ice failing to regrow by June — twice that of  the previous lowest June value.

Simon Josey and colleagues analysed satellite and near-ocean surface atmospheric data and found three areas of anomalously low sea-ice cover in winter 2023, with the strongest reductions being 80% relative to the 1991–2020 June–July average. This loss of ice is accompanied by an increase in the amount of heat being released into the atmosphere from the ocean, with some areas experiencing double the amount of heat loss compared to pre-2015 values. This increased heat loss is associated with increases in the frequency of storms, with the authors calculating up to an additional 7 days of storms occurring over the areas with substantial reductions in ice. In addition, changes in the transfer of heat may have implications for how the ocean circulates, specifically how the Antarctic bottom water — a deep layer of water with high density and cold temperatures in the Southern Ocean — may absorb and store heat and carbon dioxide.