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Climate projections suggest a weakening or collapse of the Atlantic Meridional Overturning Circulation (AMOC) under global warming, with evidence that a slowdown is already underway. This could have significant ramifications for Atlantic Ocean heat transport, Arctic sea ice extent and regional North Atlantic climate. However, the potential for far-reaching effects, such as teleconnections to adjacent basins and into the Southern Hemisphere, remains unclear. Here, using a global climate model we show that AMOC collapse can accelerate the Pacific trade winds and Walker circulation by leaving an excess of heat in the tropical South Atlantic. This tropical warming drives anomalous atmospheric convection, resulting in enhanced subsidence over the east Pacific and a strengthened Walker circulation and trade winds. Further teleconnections include weakening of the Indian and South Atlantic subtropical highs and deepening of the Amundsen Sea Low. These findings have important implications for understanding the global climate response to ongoing greenhouse gas increases.Changes to the Atlantic Meridional Overturning Circulation (AMOC) will have substantial regional impacts but more remote effects are unclear. Here, model analysis shows that AMOC collapse causes excess heat to accumulate in the tropical south Atlantic Ocean, resulting in atmospheric changes globally.

In 2013/14 eastern South America experienced one of its worst droughts. At the same time an unprecedented marine heatwave developed in the western South Atlantic. The drought was linked to suppression of the South Atlantic convergence zone and its associated rainfall, which led to water shortages in Brazil and impacted food supplies globally. Here we show from observations that such droughts and adjacent marine heatwaves have a common remote cause. Atmospheric blocking triggered by tropical convection in the Indian and Pacific oceans can cause persistent anticyclonic circulation that not only leads to severe drought but also generates marine heatwaves in the adjacent ocean. We show that increased shortwave radiation due to reduced cloud cover and reduced ocean heat loss from weaker winds are the main contributors to the establishment of marine heatwaves in the region. The proposed mechanism, which involves droughts, extreme air temperature over land and atmospheric blocking explains approximately 60% of the marine heatwave events in the western South Atlantic. We also identified an increase in frequency, duration, intensity and extension of marine heatwave events over the satellite period 1982–2016. Moreover, surface primary production was reduced during these events with implications for regional fisheries.

The Indian Ocean has warmed rapidly and notably at a faster rate than the other tropical ocean basins in the latter half of the twentieth century. We conduct sensitivity experiments using an atmospheric general circulation model to determine the impact of Indian Ocean surface warming on large-scale global atmospheric circulation trends and rainfall distribution, in terms of its pattern and magnitude. Indian Ocean warming drives changes in the local Indian Ocean Walker cell that leads to anomalous easterlies over the Pacific Ocean and strengthens the Pacific Walker Circulation. The anomalous Indian Ocean Walker cell results in anomalous subsidence over Central Africa and the tropical Atlantic, where it is associated with a precipitation decrease over the equator. During austral summer, Indian Ocean warming is associated with the intensification of the northern hemisphere Hadley cell and strengthening of the extratropical atmospheric circulation resembling a positive North Atlantic Oscillation. During austral winter, it is associated with weakening of the southern hemisphere Hadley cell and strengthening of a positive Southern Annular Mode pattern. More intensive warming in the western region of the Indian Ocean basin compared to the east has a significant impact on rainfall trends in the basin, easterly wind trend in the western Pacific and intensity of Hadley circulation changes. It is, however, the Indian Ocean warming across the entire basin that dominates the drying of the tropical Atlantic and the trends in extratropical modes of variability. This study suggests the Indian Ocean warming could have potentially influenced global atmospheric circulation trends observed in the recent decades.

Australia is one of the regions strongly affected by the El Niño‐Southern Oscillation (ENSO). The recent 2020–2023 La Niña event was marked by record‐breaking rainfall and flooding across eastern Australia. The continuous wet conditions during the triple La Niña motivated us to explore the impacts of single‐year and multi‐year ENSO events on Australian rainfall using observational data sets. We find that, while there is no difference in the rainfall impacts during single or double El Niño events, Australian rainfall tends to increase in the third year of triple La Niña events compared to the first and second years. The enhanced rainfall impact during the third La Niña year occurs despite no strengthening of La Niña in the tropical Pacific, suggesting that other processes such as local rainfall‐soil moisture feedback may play a role in prolonging the effects of multi‐year La Niña events in Australia. Plain Language Summary Australia is strongly affected by the El Niño‐Southern Oscillation (ENSO), with rainfall more likely to increase during La Niña and below‐average rainfall more common during El Niño. The recent 2020–2023 multi‐year La Niña was marked by continuous wet conditions across eastern Australia, leading to record‐breaking rainfall and flooding. Multi‐year La Niña events, where La Niña occurs in two or three consecutive austral summers, happened in about 50% of all La Niña events, including five triple La Niña events since 1900. We explored the impacts of multi‐year ENSO events on Australian rainfall and found that, while there is no difference in the rainfall impacts during single or double El Niño events, rainfall tends to increase in the third year of triple La Niña events compared to the first and second years. This rainfall increase occurs despite no strengthening of La Niña in the tropical Pacific Ocean, suggesting that local processes such as feedback between high/saturated soil moisture and rainfall may play a role in prolonging the effects of multi‐year La Niña events in Australia. Key Points Eastern Australia tends to experience record‐breaking rainfall and flooding during La Niña events Rainfall impact of multi‐year El Niño‐Southern Oscillation (ENSO) persists during double and triple events, despite no strengthening of ENSO Australian rainfall increases in the third year of triple La Niña likely due to soil moisture‐rainfall feedback

The 2010–2011 La Niña caused a sharp but temporary drop in global sea level due to increased rainfall and terrestrial water storage primarily in Australia. However, whether similar responses occurred in other La Niña events remains unclear. Here we investigate analogous impacts during other El Niño‐Southern Oscillation (ENSO) events using available sea level height observations during 1993–2022. We find that ENSO consistently drives changes in terrestrial and oceanic precipitation, land water storage, and sea surface salinity. These changes cause temporary global sea level declines during La Niña and increases during El Niño, with the most pronounced variations occurring during the build‐up phase of ENSO. A strong negative relationship between terrestrial precipitation and global mean sea level underscores the critical role of ENSO‐driven global water redistribution. Northern South America consistently experienced water storage gains during La Niña and declines during El Niño, whereas water storage changes in Australia were inconsistent.

This study investigates interseasonal and interevent variations in the impact of El Niño on Australian rainfall using available observations from the postsatellite era. Of particular interest is the difference in impact between classical El Niño events wherein peak sea surface temperature (SST) anomalies appear in the eastern Pacific and the recently termed El Niño “Modoki” events that are characterized by distinct warm SST anomalies in the central Pacific and weaker cold anomalies in the west and east of the basin. A clear interseasonal and interevent difference is apparent, with the maximum rainfall response for Modoki events occurring in austral autumn compared to austral spring for classical El Niños. Most interestingly, the Modoki and non-Modoki El Niño events exhibit a marked difference in rainfall impact over Australia: while classical El Niños are associated with a significant reduction in rainfall over northeastern and southeastern Australia, Modoki events appear to drive a large-scale decrease in rainfall over northwestern and northern Australia. In addition, rainfall variations during March–April–May are more sensitive to the Modoki SST anomaly pattern than the conventional El Niño anomalies to the east.

The tropical Pacific Ocean is a key regulator of Earth's climate, with teleconnections that influence remote locations all around the world. Here we use partially coupled climate model experiments to show that tropical Pacific cooling related to an abrupt Atlantic Meridional Overturning Circulation (AMOC) slowdown can strengthen the AMOC by ∼25%. This tropical‐extratropical teleconnection occurs initially via atmospheric Rossby waves propagating from the tropical Pacific to the North Atlantic which alter surface climate conditions locally. These changes facilitate ocean heat loss from the subpolar gyre, favoring enhanced oceanic convection. The AMOC strengthening is subsequently enhanced by anomalous northward salt advection in the Atlantic, with a potential contribution from oceanic wave adjustment triggered by increased Southern Ocean westerly winds. These results highlight the influence of the tropical Pacific on the AMOC on multidecadal timescales and suggest that cold phases of tropical Pacific decadal variability could drive temporary strengthening of the AMOC. Plain Language Summary Changes in the tropical Pacific sea surface temperature can exert significant remote weather and climate impacts via physical mechanisms known as teleconnections. In this study, we report unexplored teleconnections to the Atlantic basin which act in a timescale of decades. In particular we found that a mean cooling in the tropical Pacific could act to accelerate a large‐scale ocean circulation in the Atlantic basin known as the Atlantic Meridional Overturning Circulation (AMOC). This occurs via atmospheric and oceanic waves which propagate to the North Atlantic and alter local conditions, favoring the acceleration of the AMOC. Key Points Tropical Pacific cooling can drive a strengthening of the Atlantic Meridional Overturning Circulation (AMOC) The Pacific–North Atlantic teleconnection occurs via both atmospheric and oceanic planetary waveguides Pacific–AMOC teleconnections can be induced on a multidecadal time‐scale

Large-scale modes of atmospheric variability in the southern midlatitudes can influence Antarctic sea ice concentrations (SIC) via diverse processes. For instance, variability in both the Southern Annular Mode (SAM) and zonal wave 3 (ZW3) have been linked to the abrupt 2015/16 sea ice decline. While SIC responses to each of SAM and ZW3 have been examined previously, their interaction and synchronous impact on Antarctic sea ice has not. Here, we investigate SAM/ZW3 interactions and their associated combined impacts on Antarctic sea ice using a 1200-yr simulation from a state-of-the-art climate model. Our results suggest that zonal wind anomalies associated with SAM drive SIC anomalies in the marginal ice-zone via advection of ice normal to the ice edge and Ekman drift. In contrast, meridional wind anomalies associated with ZW3 can have opposing dynamic and thermodynamic effects on SIC. Both SAM- and ZW3-related SIC anomalies propagate eastward, likely by the Antarctic Circumpolar Current. The interaction of SAM and ZW3 leads to interesting regional SIC responses. During negative SAM, ZW3-associated meridional wind anomalies across western Antarctica are closer to the ice edge and have a stronger impact on sea ice overall. ZW3 phase affects meridional wind anomalies across the whole ice edge, whereas it affects SIC anomalies mainly over western Antarctica. In parts of eastern Antarctica, SIC anomalies are less sensitive to ZW3 phase, but are sensitive to SAM, particularly in locations where the ice edge has a prominent angle relative to the SAM-related zonal wind anomalies.

Since 1995, a large region of Australia has been gripped by the most severe drought in living memory, the so‐called “Big Dry”. The ramifications for affected regions are dire, with acute water shortages for rural and metropolitan areas, record agricultural losses, the drying‐out of two of Australia's major river systems and far‐reaching ecosystem damage. Yet the drought's origins have remained elusive. For Southeast Australia, we show here that the “Big Dry” and other iconic 20th Century droughts, including the Federation Drought (1895–1902) and World War II drought (1937–1945), are driven by Indian Ocean variability, not Pacific Ocean conditions as traditionally assumed. Specifically, a conspicuous absence of Indian Ocean temperature conditions conducive to enhanced tropical moisture transport has deprived southeastern Australia of its normal rainfall quota. In the case of the “Big Dry”, its unprecedented intensity is also related to recent higher temperatures.

Moisture is the fundamental basis for precipitation, and understanding the sources of moisture is crucial for comprehending changes in precipitation patterns. Lagrangian models have been employed for moisture tracking in both extreme weather events and climatological studies as a means to gain insight into driving physical processes. Lagrangian moisture tracking models follow independent air parcels based on a set of defined assumptions. Despite the existence of many Lagrangian models and studies applying them for moisture tracking, these assumptions are seldom thoroughly tested. In this study, we use the Lagrangian model BTrIMS to demonstrate the impact of these assumptions on the results of moisture source identification. In particular, we test the method's dependence on the number of parcels released; the height that parcels are released; the vertical movement of air parcels; the vertical well-mixed assumption that lead to different moisture identification methods along trajectories, the within-grid interpolation method and the back-trajectory time step. We find that releasing approximately 200 air parcels per day from each grid point, is necessary to obtain accurate results for a region of 10 grid points or more (an area of ∼ 9000 km2 in this case). The distribution among different time steps in a day is determined based on precipitation rates. Additionally, the vertical movement of air parcels, their release height, and along-trajectory identification method of moisture substantially affect the identified moisture sources, whereas within-grid interpolation and back-trajectory time step within a reasonable range have a relatively minor role on the results. The theoretical basis of these assumptions involve precipitation formation height, vertical mixing of surface evapotranspiration, and numerical noise, all of which must be carefully considered for realistic results. Based on the results of sensitivity tests and analysis of underlying mechanisms behind the assumptions, we improve the Lagrangian model BTrIMS1.0 to a new version (BTrIMS1.1) for broader applicability. The findings of this study provide critical information for improving Lagrangian moisture source identification methods in general and will benefit future research in this field, including studies examining changes in moisture sources due to climate change.