Interdecadal Pacific Oscillation Research Articles

Interaction Between the Interdecadal Pacific Oscillation and Atlantic Multidecadal Variability Lowers Their Contemporaneous Correlation

AbstractThe Interdecadal Pacific Oscillation (IPO) and Atlantic Multidecadal Variability (AMV) substantially affect global climate system. Model studies suggested a fast interaction between the IPO and AMV through atmospheric teleconnections, but observations exhibit a weak IPO–AMV contemporaneous correlation. To address this paradox, we apply linear inverse model (LIM) in observations to decode the interaction. We reveal that a cancel effect of the interaction lowers the observed IPO–AMV contemporaneous correlation. When only retaining the one‐way modulation (the IPO forces the AMV or the reversed one) in the observational LIM, their correlation peaks nearly simultaneously, consistent with the fast IPO–AMV interaction in model experiments. We further demonstrate that the fast interaction is associated with both tropical and extratropical processes. Our study reconciles the discrepancy between observations and models on the IPO–AMV interaction.

How does globally accumulated tropical cyclone energy vary in response to a changing climate?

How does globally accumulated tropical cyclone energy vary in response to a changing climate?

Cause of the Recent Tendency of Tropical Cyclones Approaching Coasts as Revealed by HighResMIP-PRIMAVERA Simulations

Abstract Tropical cyclones developing over the ocean threaten society when they approach land. A recent study has shown that the global mean distance of tropical cyclones at their lifetime maximum intensity (LMI) to the land has decreased over the last 40 years. However, whether this trend is due to global warming or natural variability still needs to be determined. This study aims to identify the primary driver of the observed trend. We analyzed both atmosphere-only and coupled simulations following the CMIP6 High Resolution Model Intercomparison Project (HighResMIP) protocol with global models from the PRIMAVERA project. The former can depict the responses to anthropogenic forcing and natural climate variability constrained by sea surface temperature (SST), while the latter can reproduce only the forced response. The observed LMI distance shows statistically significant trends in the Pacific basin. For this basin, model results indicate that the atmosphere-only simulations reproduced the observed trend of the LMI distance, but the atmosphere–ocean coupled simulations did not, suggesting that the observed trend is not due to global warming but to natural variability. The results of atmospheric-only simulations supported the previously proposed hypothesis based on the observational evidence that the low-frequency variability of SST and the LMI distance to the coasts are linked by the atmospheric steering wind anomaly associated with the Pacific decadal oscillation (PDO) or, equivalently, the interdecadal Pacific oscillation (IPO), suggesting that the recent decadal trend in the LMI distance is driven by natural low-frequency SST variability. These findings bear societal significance, as the recently observed trend may not persist with progressing global warming but depends on future changes in PDO/IPO. Significance Statement In recent years, a tendency has been observed for tropical cyclones to become closer to the land at their strongest stage. We want to understand whether this trend will continue in the future due to global warming or whether it may change due to climate variability, but it is difficult to elucidate from only observational data. Therefore, we analyzed multiple global simulation data. Through this analysis, we checked the reproducibility of the observed trend in the models and used statistical methods to explore the factors behind the trend. The results suggest that the trend is not primarily driven by global warming but rather by decadal natural variability in the Pacific sea surface temperatures. Therefore, the observed recent trend may not continue in the future.

Investigation on the Linkage Between Precipitation Trends and Atmospheric Circulation Factors in the Tianshan Mountains

The Tianshan Mountains are located in the hinterland of the Eurasian continent, spanning east to west across China, Kazakhstan, Kyrgyzstan, and Uzbekistan. As the primary water source for Central Asia’s arid regions, the Tianshan mountain system is pivotal for regional water security and is highly sensitive to the nuances of climate change. Utilizing ERA5 precipitation datasets alongside 24 atmospheric circulation indices, this study delves into the variances in Tianshan’s precipitation patterns and their correlation with large-scale atmospheric circulation within the timeframe of 1981 to 2020. We observe a seasonally driven dichotomy, with the mountains exhibiting increasing moisture during the spring, summer, and autumn months, contrasted by drier conditions in winter. There is a pronounced spatial variability; the western and northern reaches exhibit more pronounced increases in precipitation compared to their eastern and southern counterparts. Influences on Tianshan’s precipitation patterns are multifaceted, with significant factors including the North Pacific Pattern (NP), Trans-Niño Index (TNI), Tropical Northern Atlantic Index (TNA*), Extreme Eastern Tropical Pacific SST (Niño 1+2*), North Tropical Atlantic SST Index (NTA), Central Tropical Pacific SST (Niño 4*), Tripole Index for the Interdecadal Pacific Oscillation [TPI(IPO)], and the Western Hemisphere Warm Pool (WHWP*). Notably, NP and TNI emerge as the predominant factors driving the upsurge in precipitation. The study further reveals a lagged response of precipitation to atmospheric circulatory patterns, underpinning complex correlations and resonance cycles of varying magnitudes. Our findings offer valuable insights for forecasting precipitation trends in mountainous terrains amidst the ongoing shifts in global climate conditions.

Contrasting the roles of regional anthropogenic aerosols from the western and eastern hemispheres in driving the 1980–2020 Pacific multi-decadal variations

Abstract. The multi-decadal variations in the Pacific climate are extensively discussed as being influenced by external forcings such as greenhouse gases (GHGs) and anthropogenic aerosols (AAs). Unlike GHGs, the potential impacts of AAs could be more complex because of the heterogeneity of spatial distribution during the past few decades. Here we show, using regional aerosol forcing large-ensemble simulations with the Community Earth System Model 1 (CESM1), that the increasing fossil-fuel-related aerosol emissions over Asia (EastFF) and the reduction in aerosol emissions over North America and Europe (WestFF) have remarkably different impacts on driving the Pacific circulations and sea surface temperature (SST) changes since the 1980s. EastFF excites a typical El Niño-like SST pattern in the tropical Pacific and weakens the climatological Pacific Walker circulation. WestFF induces a central Pacific (CP)-type El Niño-like SST pattern with warming in the middle region of the equatorial Pacific, which is consistent with the second leading empirical orthogonal function (EOF) pattern of the observation. Over the North Pacific region, EastFF, located at low to middle latitudes, favors an Interdecadal Pacific Oscillation (IPO)-like SST pattern (horseshoe-like SST pattern in the North Pacific) through a teleconnection pathway between the tropical and extratropical Pacific but is overwhelmed by internal variability evolving from a positive phase to a negative IPO phase. In contrast, WestFF, located at middle to high latitudes, strongly affects the North Pacific via a west-to-east mid-latitude pathway and induces extensive warming. The competing effects of the heterogeneously distributed regional aerosol forcings are expected to exhibit different patterns in the near future, especially the redistribution of aerosol emissions within the domain of EastFF (i.e., from East Asia to South Asia) and changes in aerosol composition. The complex future changes in anthropogenic aerosol emissions are likely to introduce more profound impacts of aerosol forcing on the Pacific multi-decadal variations.

Recent increase in surface melting of West Antarctic ice shelves linked to Interdecadal Pacific Oscillation

Since the late 1990s, summer surface melt across ice shelves in the Ross-Amundsen Sea sector of West Antarctica increased significantly, as demonstrated by satellite measurements and MetUM simulations. This contrasts with the period from 1979 to the late 1990s, which witnessed a decreasing summer melt trend driven by the positive trend in Southern Annular Mode. The increase in summer melt since the late 1990s is linked to an increase in geopotential height and intensified anticyclonic blocking along coastal West Antarctica, which strengthened northerly winds over the Ross-Amundsen Sea sector, leading to enhanced advection of warm, marine air. Our analysis reveals a strong connection between summer melt indices and sea surface temperatures in the South Pacific Convergence Zone during this period. Moreover, increased summer precipitation in South Pacific Convergence Zone since the late 1990s strengthened the Rossby wave teleconnection toward West Antarctica, contributing to enhanced blocking along the coastal region. This is consistent with the transition of the Interdecadal Pacific Oscillation to its negative phase.

Interdecadal changes in three-dimensional atmospheric circulation patterns related to summer temperature variability in Eastern China modulated by the interdecadal Pacific Oscillation

Abstract The dynamic effects of three-dimensional atmospheric circulation patterns are critical for regulating both regional and global climates. By using the three-pattern decomposition of global atmospheric circulation (3P-DGAC), this study recognizes the interdecadal changes of three-dimensional atmospheric circulation patterns associated with summer temperature anomalies in the middle and lower reaches of Yangtze River (MLRYR), and further demonstrates that these related changes of atmospheric circulation patterns are modulated by the Interdecadal Pacific Oscillation (IPO). During the positive phase of the IPO, the three-dimensional atmospheric circulation patterns are characterized by the anticyclonic high at the middle and upper troposphere, and anomalous downdrafts along local meridional circulation near MLRYR. Then, in the negative phase of the IPO, alongside the aforementioned atmospheric circulation patterns, there are anomalous downdrafts along the local zonal circulation at the Eastern Tibetan Plateau (ETP). Through statistical and dynamical analysis, the emergence of local zonal circulation is attributed to the influences of positive sea surface temperature anomalies in North Atlantic during the negative phase of the IPO, which propagate to East Asia through intensified jet stream waviness. The findings of this study establish a synchronous linkage between ETP climate and downstream regions, offering significant implications for enhancing seasonal climate forecasting in the future.

A pioneering approach to deterministic rainfall forecasting for wet period in the Northern Territory of Australia using machine learning

Several studies investigated the effect of large-scale climatic modes on rainfall in tropical climatic zone of Australia. In the current study, machine learning models such as artificial neural networks (ANN) and random forest (RF) were used to forecast the wet-period rainfall (Austral summer: December-February) at six different stations of Northern Territory (NT), Australia. To examine the synchronous influence of potential predictors on wet-period rainfall of NT, multiple input sets with different combinations of lagged Indian Ocean Dipole (IOD), Southern Oscillation Index (SOI), Interdecadal Pacific Oscillation (IPO), and Madden Julian Oscillation (MJO) were investigated. To assess the superiority of machine learning models over traditional linear regression (MR) model, the linear models were also developed for the same study locations. The model performance was evaluated using five distinct statistical metrics, including the root mean square error (RMSE), coefficient of determination (R2), relative root mean square error (rRMSE), relative mean bias (rBias), and Nash-Sutcliffe coefficient (NSC). Large-scale climate factors, primarily MJO, SOI, and Niño3.4, were found to have a considerable effect on NT wet-period rainfall, which can be used for future rainfall forecasting. It is found that among the studied models, the ANN model delivered the best results with the least RMSE ranging from 0.47 to 1.72, along with coefficient of determination values ranging from 0.84 to 0.91. Whereas, for the RF and MR models, produced results were having RMSE values ranging 0.83 ~ 2.28 and 2.52 ~ 4.19 respectively, and R2 values ranging 0.79 ~ 0.86 and 0.62 ~ 0.72 respectively.

Interdecadal Variation of Springtime Compound Temperature‐Precipitation Extreme Events in China and Its Association With Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation

AbstractThe concurrent occurrence of temperature and precipitation extremes, known as compound temperature‐precipitation extreme events (CTPEEs), leads to more pronounced consequences for human society and ecosystems than when these extremes occur separately. However, such compound extremes have not been sufficiently studied, especially during boreal spring. Spring is an important transition season, during which the CTPEEs plays a pivotal role in plant growth and revival of terrestrial ecosystems. This study investigates the spatio‐temporal variation characteristics of spring CTPEEs in China, including warm‐dry, warm‐wet, cold‐dry, and cold‐wet combinations. The compound cold‐wet extreme events occur most frequently, followed by warm‐dry, warm‐wet, and cold‐dry events. The frequency of CTPEEs associated with warm (cold) extremes shows a marked interdecadal increase (decrease) around the mid‐to‐late 1990s. It is found that the interdecadal change in CTPEEs is primarily determined by the variation in temperature extremes. This interdecadal shift coincides with the phase transitions of the Atlantic Multidecadal Oscillation (AMO) and the Interdecadal Pacific Oscillation (IPO). After the mid‐to‐late 1990s, the configuration of a positive AMO and a negative IPO excited atmospheric wave trains over mid‐high latitudes, causing high‐pressure and anticyclonic anomalies over East Asia. This leads to less cloudiness, allowing an increase in downward solar radiation, which enhances surface warming and contributes to an increase (decrease) in warm‐dry and warm‐wet extremes. The above observations are confirmed by the Pacemaker experiments. The results of this study highlight a significant contribution of internal climate variability to interdecadal changes in CTPEEs at the regional scale.

Simulated Antarctic sea ice expansion reconciles climate model with observation

Observations reveal Antarctic sea ice expansion and Southern Ocean surface cooling trends from 1979 to 2014, whereas climate models mostly simulate the opposite. Here I use historical ensemble simulations with multiple climate models to show that sea-ice natural variability enables the models to simulate an Antarctic sea ice expansion during this period under anthropogenic forcings. Along with sea-ice expansion, Southern Ocean surface and subsurface temperatures up to 50oS, as well as lower tropospheric temperatures between 60oS and 80oS, exhibit significant cooling trends, all of which are consistent with observations. Compared to the sea-ice decline scenario, Antarctic sea ice expansion brings tropical precipitation changes closer to observations. Neither the Southern Annular Mode nor the Interdecadal Pacific Oscillation can fully explain the simulated Antarctic sea ice expansion over 1979–2014, while the sea-ice expansion is closely linked to surface meridional winds associated with a zonal wave 3 pattern.

The Relative Contributions of Internal Variability and External Forcing to Pacific Walker Circulation over the Last Millennium

Abstract Pacific Walker circulation (PWC) is an important component of tropical atmospheric circulation. Current studies have mainly focused on PWC changes over recent decades and the near future, while less effort has been devoted to long-term PWC variations. In this study, we investigate PWC changes over the last millennium (LM) based on the Community Earth System Model LM Ensemble (CESM-LME). The simulated PWC variations show no significant trend but do reveal decadal fluctuations during the LM, which underestimate the strengthened Little Ice Age (LIA)–Medieval Climate Anomaly (MCA) PWC differences indicated by proxy-based reconstructions. A quantitative estimation of the contributions made to PWC variability from internal variability and external forcing is conducted by using multiple linear regression (MLR) analysis. The internal variabilities contribute approximately 80% to the changes in PWC during the LM, among which the interdecadal Pacific oscillation (IPO) has the largest contribution. In the positive phase of the IPO, the Indo-Pacific sea level pressure (SLP) gradient decreases, and anomalous westerlies occur in the tropical western Pacific, corresponding to a weakened PWC. The relationships between the IPO and PWC show multidecadal-to-centennial fluctuations, suggesting that other internal modes or external forcings may have modulated the IPO–PWC relationship. Volcanic forcing is also an important contributor to PWC variability during the LM. The simulated PWC significantly weakens and lasts for 1–2 years after large volcanic eruptions. The El Niño–like SST pattern and the corresponding zonal SLP gradient lead to the PWC weakening following large volcanic eruptions. Significance Statement As one of the most active components of tropical atmospheric circulation, Pacific Walker circulation (PWC) can significantly modulate global climate through atmospheric teleconnections. Previous studies have mainly focused on PWC variability over recent warm periods and future changes. However, understanding of PWC changes is currently lacking due to limited instrumental observations. The last millennium (LM) has a rich archive of proxy records that give us a longer perspective on climate variability and change, which is an excellent period for understanding the long-term mechanisms and changes in PWC. In this study, we use simulations from the CESM-LME to quantify the relative importance of internal variability and external forcings to PWC variations during the LM. The simulated PWC variations show no significant trend but decadal fluctuations, which underestimates the reconstructed PWC variations during the LM. The internal variabilities contribute approximately 80% to the changes in PWC, among which the interdecadal Pacific oscillation (IPO) has the largest contribution. External forcing, especially the contribution made by volcanic forcing, is also nonnegligible. Both the positive phase of the IPO and large tropical volcanic eruptions could trigger El Niño–like SST anomalies, accompanied by a decreased Indo-Pacific SLP gradient and a weakened PWC.

Interannual Relationship between ENSO and Tropical Cyclone Genesis over the Southwest Indian Ocean and Its Modulation by the Interdecadal Pacific Oscillation

Interannual Relationship between ENSO and Tropical Cyclone Genesis over the Southwest Indian Ocean and Its Modulation by the Interdecadal Pacific Oscillation

A seesaw in the South Pacific western and eastern subtropical mode waters

Abstract The South Pacific Western Subtropical Mode Water (WSTMW) and Eastern Subtropical Mode Water (ESTMW) are important components of the subtropical meridional overturning cells. By synthesizing observations, reanalysis products, and eddy-resolving ocean model results, we find an interannual volume seesaw in the WSTMW and ESTMW during 1980-2020. Further analysis of the data and model outputs indicates that this volume seesaw is closely related to the El Niño–Southern Oscillation (ENSO) through its modulation of the Ekman pumping velocity, buoyancy fluxes, and mixed layer depth over the formation regions of the two water masses. This negative correlation between the WSTMW and ESTMW modulates the depth of the permanent pycnocline and directly contributes to the east-west contrast between the two water masses in their core layer properties, especially, during negative phase of the Interdecadal Pacific Oscillation (IPO) since 2000.

Climate Extremes in the New Zealand Region: Mechanisms, Impacts and Attribution

ABSTRACTAs global surface temperatures have increased with human‐induced climate change, notable compound climate extremes in the New Zealand (NZ) region associated with atmospheric heatwaves (AHWs) and marine heatwaves (MHWs) have occurred in the past 6 years. Natural modes of variability that also played a key role regionally include the Interdecadal Pacific Oscillation (IPO), El Niño/Southern Oscillation (ENSO) and changes in the location and strength of the westerlies as seen in the Southern Annular Mode (SAM). Along with mean warming of 0.8°C since 1900, a negative phase of the IPO, La Niña phase of ENSO and a strongly positive SAM contributed to five compound warm extremes in the extended austral summer seasons (NDJFM) of 1934/35, 2017/18, 2018/19, 2021/22 and 2022/23. These are the most intense coupled ocean/atmosphere (MHWs/AHWs) heatwaves on record with average temperature anomalies over land and sea +0.8°C to 1.1°C above 1991–2020 averages. The number of days above 25°C and above the 90th percentile of maximum temperature has increased, while the number of nights below 0°C and below the 10th percentile has decreased. Coastal waters around NZ recently experienced their longest MHW in the satellite era (1982‐present) of 289 days through 2023. The estimated recurrence interval reduces from 1 in 300‐years for the AHW event during the 1930s climate to a 1 in 25‐year event for the most recent decade. Consequences include major loss of ice of almost one‐third volume from Southern Alps glaciers from 2017 to 2021 with rapid melt of seasonal snow in all four cases. Above‐average temperatures in the December/January grape flowering period resulted in advances in veraison (the onset of ripening); and higher‐than‐average grape yields in 2022 and 2023 vintages. Marine impacts include widespread sea‐sponge bleaching around northern and southern NZ.

A climate change signal in the tropical Pacific emerges from decadal variability.

The eastern tropical Pacific has defied the global warming trend. There has been a debate about whether this observed trend is forced or natural (i.e., the Interdecadal Pacific Oscillation; IPO) and this study shows that there are two patterns, one that oscillates along with the IPO, and one that is emerging since the mid-1950s, herein called the Pacific Climate Change (PCC) pattern. Here we show these have distinctive and distinguishable atmosphere-ocean signatures. While the IPO features a meridionally broad wedge-shaped SST pattern, the PCC pattern is marked by a narrow equatorial cooling band. These different SST patterns are related to distinct wind-driven ocean dynamical processes. We further show that the recent trends during the satellite era are a combination of IPO and PCC. Our findings set a path to distinguish climate change signals from internal variability through the underlying dynamics of each.

Trends and Periodicities of Tropical Cyclone Frequencies and the Correlations with Ocean Drivers

This study presents a comprehensive analysis on the variations in the tropical cyclone (TC) frequencies during 1980–2021, including the linear trends, periodicities, and their variabilities on both global and basin-wise scales. An increasing trend in the annual number of global TCs is identified, with a significant rising trend in the numbers of tropical storms (maximum sustained wind 35 kts≤Umax<64 kts) and intense typhoons (Umax≥96 kts) and a deceasing trend for weak typhoons (64 kts≤Umax<96 kts). There is no statistically significant trend shown in the global Accumulated Cyclone Energy (ACE). On a regional scale, the Western North Pacific (WNP) and Eastern North Pacific (ENP) are the regions of the first- and second-largest numbers of TCs, respectively, while the increased TC activity in the North Atlantic (NA) contributes the most to the global increase in TCs. It is revealed in the wavelet transformation for periodicity analysis that the variations in the annual number of TCs with different intensities mostly show an inter-annual period of 3–7 years and an inter-decadal one of 10–13 years. The inter-annual and inter-decadal periods are consistent with those in the ENSO-related ocean drivers (via the Niño 3.4 index), Southern Oscillation Index (SOI), and Inter-decadal Pacific Oscillation (IPO) index. The inter-decadal variation in 10–13 years is also observed in the North Atlantic Oscillation (NAO) index. The Tropical North Atlantic (TNA) index and Atlantic Multi-decadal Oscillation (AMO) index, on the other hand, present the same inter-annual period of 7–10 years as that in the frequencies of all the named TCs in the NA. Further, the correlations between TC frequencies and ocean drivers are also quantified using the Pearson correlation coefficient. These findings contribute to an enhanced understanding of TC activity, thereby facilitating efforts to predict particular TC activity and mitigate the inflicted damage.

Uncovering Interdecadal Pacific Oscillation’s Dominance in Shaping Low-Frequency Sea Level Variability in the South China Sea

The low-frequency sea level variability in the South China Sea (SCS) is examined using high-resolution regional ocean model simulations that span the last six decades. The analysis reveals interdecadal oscillations with a periodicity of 12–13 years as the dominant mode of sea level variability in the SCS. The fluctuations in the Luzon Strait transport (LST) are identified as primary drivers of interannual to interdecadal sea level variability, rather than atmospheric forcing within the SCS. Fourier spectrum analysis is employed to investigate the association between SCS sea level variability and the Interdecadal Pacific Oscillation (IPO), using principal components of SCS sea surface height anomalies, wind stress curl, wind stress components, net short wave flux, as well as the LST and various climate indices. The variations in the SCS sea level are driven by the IPO, which modifies the LST and ocean heat content, impacting the steric sea level.

Pacific Interannual and Multidecadal Variability Recorded in δ18O of South American Summer Monsoon Precipitation

AbstractThe South American summer monsoon (SASM) generates important hydroclimatic impacts in (sub‐)tropical South America and isotopic tracers recorded in paleoclimatic archives allow for assessing its long‐term response to Pacific variability prior to modern observations. Stable oxygen isotopes in precipitation integrate hydroclimatic changes during the SASM mature phase from December to February (DJF) in response to the Interdecadal Pacific Oscillation (IPO) and El Niño—Southern Oscillation (ENSO), respectively. Here, results from the isotope‐enabled Community Atmosphere Model v.5 are compared with highly resolved and precisely dated isotopic records from speleothems, tree rings, lake and ice cores during the industrial era (1880–2000 CE) and validated against observations from the International Atomic Energy Agency (IAEA) network. Pacific sea surface temperatures (SSTs) are coupled to the isotopic composition of SASM precipitation through perturbations in the Walker circulation associated with low‐ (IPO) and high‐frequency (ENSO) variability, impacting convective activity over tropical South America and the tropical Atlantic. Changes in convection over this monsoon entrance region ultimately control the downstream oxygen isotopic composition of precipitation recorded in paleoclimate archives. Overall, model results, paleoclimate records and IAEA data agree on the isotopic response to Pacific SST forcing. These results highlight the potential for long isotopic paleoclimate records to reconstruct Pacific climate variability on both high‐ and low‐frequency timescales. Furthermore, the isolation of the IPO signal in a diverse set of isotopic archives invites the reinterpretation of other paleoclimate proxies for identifying this historically overlooked forcing.

Coral Sr/Ca-SST reconstruction from Fiji extending to ~1370 CE reveals insights into the Interdecadal Pacific Oscillation.

The southwestern tropical Pacific is a key center for the Interdecadal Pacific Oscillation (IPO), which regulates global climate. This study introduces a groundbreaking 627-year coral Sr/Ca sea surface temperature reconstruction from Fiji, representing the IPO's southwestern pole. Merging this record with other Fiji and central tropical Pacific records, we reconstruct the SST gradient between the southwestern and central Pacific (SWCP), providing a reliable proxy for IPO variability from 1370 to 1997. This reconstruction reveals distinct centennial-scale temperature trends and insights into Pacific-wide climate impacts and teleconnections. Notably, the 20th century conditions, marked by simultaneous basin-scale warming and weak tropical Pacific zonal-meridional gradients, deviate from trends observed during the past six centuries. Combined with model simulations, our findings reveal that a weak SWCP gradient most markedly affects IPO-related rainfall patterns in the equatorial Pacific. Persistent synchronous western and central Pacific warming rates could lead to further drying climate across the Coral Sea region, adversely affecting Pacific Island nations.

Large-Scale Climate Modes Drive Low-Frequency Regional Arctic Sea Ice Variability

Abstract Summer Arctic sea ice is declining rapidly but with superimposed variability on multiple time scales that introduces large uncertainties in projections of future sea ice loss. To better understand what drives at least part of this variability, we show how a simple linear model can link dominant modes of climate variability to low-frequency regional Arctic sea ice concentration (SIC) anomalies. Focusing on September, we find skillful projections from global climate models (GCMs) from phase 6 of the Coupled Model Intercomparison Project (CMIP6) at lead times of 4–20 years, with up to 60% of observed low-frequency variability explained at a 5-yr lead time. The dominant driver of low-frequency SIC variability is the interdecadal Pacific oscillation (IPO) which is positively correlated with SIC anomalies in all regions up to a lead time of 15 years but with large uncertainty between GCMs and internal variability realization. The Niño-3.4 index and Atlantic multidecadal oscillation have better agreement between GCMs of being positively and negatively related, respectively, with low-frequency SIC anomalies for at least 10-yr lead times. The large variations between GCMs and between members within large ensembles indicate the diverse simulation of teleconnections between the tropics and Arctic sea ice and the dependence on the initial climate state. Further, the influence of the Niño-3.4 index was found to be sensitive to the background climate. Our results suggest that, based on the 2022 phases of dominant climate variability modes, enhanced loss of sea ice area across the Arctic is likely during the next decade. Significance Statement The purpose of this study is to better understand the drivers of low-frequency variability of Arctic sea ice. Teasing out the complicated relationships within the climate system takes a large number of examples. Here, we use 42 of the latest generation of global climate models to construct a simple linear model based on dominant named climate features to predict regional low-frequency sea ice anomalies at a lead time of 2–20 years. In 2022, these modes of variability happen to be in the phases most conducive to low Arctic sea ice concentration anomalies. Given the context of the longer-term trend of sea ice loss due to global warming, our results suggest accelerated Arctic sea ice loss in the next decade.