The Arctic has experienced significant sea ice decline, particularly since the late 1990s, largely attributed to rising greenhouse gas concentrations and associated surface temperature increases. While a direct link between CO2 emissions and sea ice loss has been established, the role of indirect, remote effects remains an area of active research. These indirect effects often involve large-scale atmospheric and oceanic circulations, transporting heat and moisture from lower latitudes to the Arctic. The Indo-Pacific Warm Pool (IPWP), a vast expanse of warm water in the tropical Indian and western Pacific Oceans, has shown a warming trend in recent decades, primarily due to increasing greenhouse gas concentrations and partially due to the Pacific Decadal Oscillation. Previous studies have explored isolated aspects of IPWP influence on Arctic sea ice variability but haven't fully elucidated the broader impact of IPWP dynamics. This study aims to investigate the remote influence of IPWP warming on Arctic sea ice loss through a combination of observational data analysis and numerical modeling. The study focuses on understanding the mechanisms connecting IPWP warming to sea ice loss and introduces a novel concept, the "Arctic capacitor effect of the IPWP", to explain the relationship between greenhouse gas emissions and Arctic sea ice loss via a remote pathway.

Decades of research demonstrate a robust decline in Arctic sea ice, predominantly linked to increasing greenhouse gas concentrations and the subsequent rise in surface temperatures. Parkinson and Simmonds highlight the long-term trends and variability in polar sea ice, and Notz and Stroeve quantified the direct relationship between global CO2 emissions and September sea ice extent. However, the complexities of atmosphere-snow-ice-ocean interactions, coupled with numerous positive feedback mechanisms, necessitate a deeper understanding of both direct and indirect forcing mechanisms. Existing research suggests indirect effects via large-scale atmospheric and oceanic processes, transporting heat and moisture from lower latitudes. Studies have pointed towards specific large-scale processes, but the relative importance of these mechanisms requires further investigation. The IPWP has been identified as an important player in influencing climate variability globally, with studies showing its impact on monsoons, ENSO characteristics, and Arctic climate. While some research has explored links between specific parts of the IPWP and Arctic sea ice, the overall impact of IPWP dynamics remains largely unclear. This study contributes to this understanding by exploring the comprehensive influence of the IPWP on Arctic sea ice using a broader, multi-faceted approach.

This research employs a multi-faceted approach to investigate the relationship between IPWP warming and Arctic sea ice loss. The study utilizes several datasets, including the NOAA Extended Reconstructed SST Version 5 (ERSSTv5) for sea surface temperature, NSIDC Sea Ice data for sea ice concentration, and ECMWF ERA5 reanalysis data for atmospheric variables, covering various time periods and spatial resolutions. CMIP6 model simulations from 49 global climate models are also included to support the findings. The IPWP index is defined as the area-averaged SST within a specified region (60°E–170°E longitude and 15°S–15°N latitude). The study performs regression analyses to identify correlations between the IPWP index and Arctic sea ice concentration, focusing on boreal autumn (October-December). Detrending techniques are applied to isolate the influence of IPWP variability from direct CO2 effects on sea ice. The study quantifies the contribution of IPWP warming to sea ice loss by calculating the ratio of the IPWP-related sea ice trend to the total trend. To investigate the underlying mechanisms, further regression analyses of atmospheric variables (mean sea level pressure, wind field, 2-m air temperature, accumulated downward longwave radiation, specific humidity, and vertical velocity) onto the detrended IPWP index are performed. The study also explores Rossby wave dynamics and transient eddy feedback to clarify the atmospheric pathways linking IPWP warming to Arctic sea ice loss. Furthermore, idealized numerical experiments using the Community Atmosphere Model version 5 (CAM5) are conducted to validate the statistical findings. These experiments involve introducing a 2°C temperature increase in the IPWP region and examining the resulting impact on Arctic atmospheric circulation and sea ice. Additional experiments consider SST anomalies across various ocean basins to account for possible broader influences.

The study reveals a statistically significant negative correlation (coefficients ranging from -0.33 to -0.71, p < 0.01) between the autumnal IPWP index and sea ice concentration in the broader Arctic region encompassing Hudson Bay, Baffin Bay, and the Labrador Sea. This correlation persists across various time periods (1979-2020, 1900-2015) and datasets, including CMIP6 model simulations. The IPWP-related sea ice trend accounts for approximately 45% of the total sea ice loss in the region. Regression analysis indicates a linkage between IPWP warming, a negative phase of the Arctic Oscillation (AO), anomalous high pressure over Greenland, warm air advection, increased downward longwave radiation, and reduced sea ice concentration. The analysis suggests that IPWP warming enhances tropical convection, generating a planetary wavetrain that propagates northeastward, influencing the Arctic vortex and ultimately impacting sea ice. The numerical experiments using CAM5 support the statistical findings, showing a weakening of the Arctic polar vortex and increased high-pressure anomalies over the Arctic in response to IPWP warming, consistent with the observed negative AO pattern. Additional numerical experiments incorporating broader SST anomalies strengthen the observed relationships, demonstrating a robust connection between IPWP and Arctic atmospheric circulations.

The findings strongly support a significant and previously underappreciated link between IPWP warming and autumnal Arctic sea ice loss in the specified region. The "Arctic capacitor effect of the IPWP" concept is introduced, proposing that the IPWP acts as a reservoir for greenhouse warming signals. This stored energy is released via intensified convection, leading to atmospheric teleconnections affecting the Arctic vortex and promoting sea ice decline. While the study focuses on the autumnal period, the lead-lag relationships observed suggest a potential influence extending into the following boreal winter. The study's results emphasize the crucial role of tropical oceans in influencing polar climate, highlighting that greenhouse gas-induced warming in the tropics can exert a substantial indirect influence on Arctic sea ice loss. The results also highlight the importance of considering both direct and indirect forcing mechanisms when studying Arctic sea ice changes.

This study provides novel insights into the complex mechanisms driving Arctic sea ice loss by demonstrating a significant link between IPWP warming and sea ice decline in northeastern Canada during autumn. The introduction of the "Arctic capacitor effect of the IPWP" offers a new framework for understanding the remote influence of greenhouse gas-induced warming on Arctic sea ice. The results underscore the importance of considering both direct and indirect forcing mechanisms and highlight the significant role of tropical oceans in shaping polar climate. Future research should focus on fully coupled climate models to validate the findings and explore the potential extension of this "capacitor effect" to other tropical and subtropical ocean regions.

While the study provides compelling evidence for the link between IPWP warming and Arctic sea ice loss in the specified region, it is primarily based on statistical analysis. Further validation is needed through fully coupled atmosphere-ocean-sea-ice-land model experiments to confirm the robustness of the proposed mechanisms. The study's focus on a specific Arctic region limits the generalizability of findings to other Arctic areas. Additionally, while the study primarily focuses on the IPWP’s influence, it acknowledges the importance of other internal climate modes (e.g., PDO, AMO) which also influence sea ice dynamics and could be interacting with the described mechanisms. Further research is needed to fully understand the relative contributions of these different climate modes.