Strong impact of the rare three-year La Niña event on Antarctic surface climate changes in 2021–2023

Abstract

From 2021 to 2023, satellite records reveal that February Antarctic sea ice extent reached record lows in 2022 and 2023. Simultaneously, the Antarctic ice sheet experienced a transient mass gain and rebounded temporarily from a decadal decline since 2002. The reasons behind these dramatic changes are unknown. Here, we show that the triple-dip La Niña event during 2021–2023 (referred to as TD_LN2023) played a major role in these changes. Compared to a previous triple-dip La Niña event (1999–2001), the tropical-Antarctic teleconnections during TD_LN2023 were stronger. A more pronounced southward shift of the Ferrel Cell was identified as a key driver for the enhanced tropical-Antarctic teleconnections during TD_LN2023 against the background of intensified westerly winds and tropical expansion. The poleward increase, which facilitated poleward atmospheric heat and moisture transport, contributed to the sea ice extent decline and the ice sheet mass growth. Additionally, this southward shift strengthened the Rossby wave train, which, sustained by enhanced stratosphere-troposphere coupling, amplified the Pacific-South American pattern, and further promoted regional sea ice decline. Finally, this southward shift, associated with the southward shift of the westerly jet, enhanced Ekman suction, bringing subsurface warm water to the surface and contributing to pan-Antarctic low sea ice. The physical processes outlined in the case study are further validated through empirical orthogonal function and regression analysis. Under global warming, multi-year La Niña events are projected to occur more frequently. The evolving tropical-Antarctic teleconnections in the context warrant close attention.