Extensive research has improved our understanding and forecast of the occurrence, evolution, and global impacts of the El Niño–Southern Oscillation (ENSO). However, ENSO changes as the global climate warms up and it exhibits different characteristics and climate impacts in the 21^st century from the 20th century. Climate models project that ENSO will also change in the warming future and have not reached an agreement about the flavor, as for the intensity and the frequency, of future ENSO conditions. This article presents the conventional view of ENSO properties, dynamics, and teleconnections and reviews the emerging understanding of the diversity and associated climate impacts of ENSO. It also reviews the results from investigations into the possible changes in ENSO under the future global warming scenarios.

Near-surface air temperature at the Argentinian research base Esperanza on the northern tip of the Antarctic Peninsula reached 18.3 °C on 6 February 2020, which is the highest temperature ever recorded on the entire Antarctic continent. Here we use weather observations since 1973 together with the ERA5 reanalysis to investigate the circulation that shaped the 2020 event, and its context over the past decades. We find that, during the 2020 event, a high-pressure ridge over the 40°-100°W sector and a blocking high on the Drake Passage led to an anticyclonic circulation that brought warm and moist air from the Pacific Ocean to the Antarctic Peninsula. Vertical air flows in a foehn warming event dominated by sensible heat and radiation made the largest contribution to the abrupt warming. A further analysis with 196 extreme warm events in austral summer between 1973 and 2020 suggests that the mechanisms behind the 2020 event form one of the two most common clusters of the events, exhibiting that most of the extreme warm events at Esperanza station are linked to air masses originating over the Pacific Ocean.

Model warming projections, forced by increasing greenhouse gases, have a large inter-model spread in both their geographical warming patterns and global mean values. The inter-model warming pattern spread (WPS) limits our ability to foresee the severity of regional impacts on nature and society. This paper focuses on uncovering the feedbacks responsible for the WPS. Here, we identify two dominant WPS modes whose global mean values also explain 98.7% of the global warming spread (GWS). We show that the ice-albedo feedback spread explains uncertainties in polar regions while the water vapor feedback spread explains uncertainties elsewhere. Other processes, including the cloud feedback, contribute less to the WPS as their spreads tend to cancel each other out in a model-dependent manner. Our findings suggest that the WPS and GWS could be significantly reduced by narrowing the inter-model spreads of ice-albedo and water vapor feedbacks, and better understanding the spatial coupling between feedbacks.

This study evaluates the capability of the Coupled Model Intercomparison Project Phase 6 (CMIP6) models to simulate El Niño‐Southern Oscillation teleconnections in the Southern Hemisphere during austral summer. The wave trains from the tropical Pacific to the Amundsen Sea are underestimated and too far westward in CMIP6 simulations. However, Atmospheric Model Intercomparison Project Phase 6 (AMIP6) experiments well capture the observed location and amplitude of the teleconnection. El Niño and La Niña‐related tropical precipitation anomalies are underestimated in CMIP6 and have their maximum amplitude too far westward, while the precipitation responses in AMIP6 simulations are similar to those observed. The weaker precipitation response in CMIP6 likely arises from a cold bias in climatological‐mean SST, which reduces the sensitivity of precipitation to SST anomalies. Increased resolution in coupled experiments eradicates the westward bias in the El Niño and La Niña‐related circulation anomalies over the Amundsen Sea, but not their insufficient amplitude.

The Maritime Continent (MC) is regarded as an important heat source region and the impact of MC heating on the West Antarctic climate which is largely controlled by the Amundsen Sea Low (ASL) is unknown. This study is focused on the impact of intensified convective heating over the MC on the variation of the ASL in the austral fall. It is observed that enhanced MC heating is linked to deepening of the eastern ASL, a feature reproduced successfully by a model experiment in which additional heating is introduced to the MC. The intensified MC heating generates anticyclonic anomalies that result in a Rossby wave source in the upper troposphere to the south of MC. Then the Rossby wave originated from the new source propagates southeastward and deepens the eastern ASL. Additional model experiments prove that the response of ASL to MC heating is stronger than that to central Pacific cooling.