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The authors show that the influence of the western Indian Ocean on Antarctic sea ice variability in austral spring has been weakening under greenhouse global warming.

The offshore heat supplied to the Antarctic continental shelves by warm eddies has a potential impact on the melting of ice shelves. Here, how warm eddies form and intrude onto the continental shelf and play an important role in ice shelf melting is shown.

The South Pacific convergence zone is a region of high precipitation spanning a vast swath of the Pacific Ocean that can shift northwards and become longitudinally oriented; such extreme zonal events have severe weather and climatic impacts and are predicted to become more frequent under greenhouse warming conditions.

Extreme positive-Indian-Ocean-dipole events cause devastating floods in eastern tropical Africa and severe droughts in Asia; increasing greenhouse gas emissions will make these dipole events about three times more frequent in the twenty-first century.

Here the authors find economic damage from El Niño far greater than benefits from La Niña on the global economy, leading to an increased economic loss as ENSO variability intensifies under greenhouse warming.

Analysis of climate models under future greenhouse-gas forcings shows that the frequency of consecutive La Niña events will increase, driven by ocean–atmosphere feedbacks that slow the heat recharge of the equatorial Pacific.

Sea surface temperature variability of the equatorial Pacific Ocean dictates the strength of El Niño–Southern Oscillation events. CMIP6 models under four IPCC emission scenarios show increased variability in the 21st century from the 20th century.

Under global warming, increased variability in El Niño sea surface temperature was projected to be detectable by about 2070. Here the authors show that the increased variability of a type of more impactful El Niño events is likely detectable by 2030.

CMIP5 simulations reveal that the frequency of extreme El Niño events doubles under the 1.5 °C Paris target, and continues to increase long after global temperatures stabilize due to emission reductions. Extreme La Niña events, however, see little change at either 1.5 °C or 2 °C warming.

The Atlantic Niño/Niña is an important mode of tropical climate variability, but how it changes with global warming is not clear. Here the authors use a comprehensive model ensemble to show that the Atlantic Niño/Niña system will probably weaken under greenhouse warming.

Extreme La Niña events occur when cold sea surface temperatures across the central Pacific Ocean create a strong temperature gradient to the Maritime continent in the west. This work projects an increase in frequency of La Niña events due to faster land warming relative to the ocean, and a greater chance of them occurring following extreme El Niño events.

Extreme El Niño events cause global disruption of weather patterns and affect ecosystems and agriculture through changes in rainfall. Model projections show that a doubling in the occurrence of such extreme episodes is caused by increased surface warming of the eastern equatorial Pacific Ocean, which results in the atmospheric conditions required for these event to occur.

The impacts of climate change on certain aspects of the El Niño/Southern Oscillation (ENSO) have been established. However, the change in sea surface temperature, commonly used to represent ENSO amplitude, remained uncertain. Now, the sea surface response is shown to be time-varying, with an increasing trend to 2040 followed by a decreasing trend. The previous uncertainty is attributed to the expectation of unidirectional behaviour and unrealistic model representations.

The ocean absorbs atmospheric heat; understanding this process is needed to predict climate change impacts. Model analysis shows the influence of the El Niño–Southern Oscillation (ENSO) on Southern Ocean heat uptake—projections with larger (smaller) ENSO amplitude show less (more) ocean warming.

The North Pacific Meridional Mode (NPMM) can trigger El Niño/Southern Oscillation (ENSO) events. Climate simulations suggest that with warming ocean temperatures, the NPMM’s impact on future ENSO strengthens, contributing to increased frequency of future extreme ENSO events and their predictability.

The strength of a positive Indian Ocean Dipole (pIOD) is set by sea surface temperature gradient across the equatorial Indian Ocean. Modelling shows warming will increase strong pIODs but decrease moderate pIODs, as faster surface warming in the west sets up conducive conditions for the strong events.

Modelling experiments show that the El Niño response to global warming is self-modulating and depends on its historical variability; if current variability is high, future variability will be low.

It is unclear how extreme positive Indian Ocean Dipole will respond to 1.5 °C of warming. Here the authors show that the frequency of these events increases linearly with warming, doubling at 1.5 °C from the pre-industrial level, but plateaus thereafter.

Despite inter-model differences in predicting the details of the eastern Pacific El Niño, a robust increase in the corresponding sea surface temperature variability under greenhouse warming is found across models.

How the shelf ocean around Antarctica changes with warming is not well known. Here, the authors show that a projected increase in El Niño–Southern Oscillation variability accelerates warming of the Antarctic shelf ocean but slows warming around the sea ice edges, thus influencing ice melt.

A sustainable global ocean observation system requires timely implementation of the framework for ocean observing. The recent Qingdao Global Ocean Summit highlighted the need for a more coherent institutional response to maintain an integrated ocean-observing system.

Although model projections indicate increased El Niño/Southern Oscillation (ENSO) variability in the future, contemporary impacts of anthropogenic forcing on ENSO variability have been difficult to ascertain. This Perspective discusses these contemporary effects, outlining that an increase in post-1960 ENSO variability is likely related to greenhouse gas forcing.

The Pacific Decadal Oscillation (PDO), a natural climate cycle, alters global climate and influences ecosystems as it varies between positive and negative phases. PDO predictability is reduced under warming as intensified ocean stratification shortens its lifespan and curtails its amplitude.

The Indian Ocean Dipole is a key mode of interannual climate variability influencing much of Asia and Australia. A Review suggests that in response to greenhouse warming, mean conditions of the Indian Ocean will shift toward a positive dipole state, but with no overall shift in the frequency of positive and negative events as defined relative to the mean climate state.

The El Niño–Southern Oscillation exerts a strong influence on the global climate, including South America, where understanding of the phenomenon first emerged. This Review outlines the impacts of the El Niño–Southern Oscillation on South America, focusing on the mechanisms and diversity of resulting teleconnections.

The El Niño–Southern Oscillation (ENSO) has global climatic implications, necessitating understanding of its observed and projected changes. This Review brings together knowledge of ENSO in a warming climate, revealing projected increases in ENSO magnitude, as well as ENSO-related rainfall and sea surface temperature variability.

A review of western boundary currents in the Pacific Ocean explores their far-reaching influence on the El Niño/Southern Oscillation, the Indonesian Throughflow, Asian monsoons, and ocean circulation in the South China Sea, and concludes that major conceptual and technical progress will be needed to close the regional mass budget and provide robust projections of Pacific western boundary currents in a changing climate.

This Review looks at the state of knowledge on the El Niño/Southern Oscillation (ENSO), a natural climate phenomenon. It discusses recent advances and insights into how climate change will affect this natural climate varibility cycle.