The Antarctic Peninsula (AP) experienced an exceptional heatwave in early February 2020, setting new temperature records across the region, including a new all-time high for the continental Antarctic region at Esperanza station (18.3 °C). This event, accompanied by extensive surface ice melting, was exceptionally widespread and intense. While the media often linked the event directly to climate change, a comprehensive analysis was lacking. This study addresses this gap by investigating the role of recent climate change in the magnitude of this 6-day regional heatwave. The Antarctic Peninsula is known for experiencing rapid warming since the 1950s, but the contribution of anthropogenic climate change to specific extreme weather events remains poorly understood. This research aims to provide the first assessment of climate change's influence on the 2020 heatwave using the analog method, a technique that compares the characteristics of the heatwave to similar atmospheric circulation patterns from the past and recent periods. The study leverages the ERA5 reanalysis dataset to reconstruct flow analogs, allowing for a quantitative assessment of how the magnitude of the event changed due to climate warming.

Prior research has documented extreme conditions in Antarctica during the 2019-2020 summer, focusing either on monthly mean temperatures or daily extremes at specific locations. Studies have linked the warming trend of the Antarctic Peninsula to various factors, including the strengthening Southern Annular Mode (SAM), tropical and mid-latitude teleconnections, and the influence of the Amundsen Sea Low and El Niño Southern Oscillation (ENSO). While the influence of anthropogenic climate change on generalized Antarctic warming is well established, its role in specific extreme events has been under-explored. Previous work has evaluated the physical mechanisms contributing to the Esperanza station record, but its relationship to climate change was not comprehensively discussed. This study builds upon these existing works by offering a regional-scale analysis of the 2020 heatwave and explicitly assessing the role of climate change.

This study employed the analog method, a technique used to evaluate changes in the magnitude of extreme weather events. The method focuses on identifying historical atmospheric circulation patterns that are similar to those that occurred during the 2020 heatwave. The ERA5 reanalysis dataset, covering the period 1950-2020, was used to construct flow analogs. The study defined two periods: a 'past' period (1950-1984) and a 'recent' period (1985-2019). For each day of the heatwave event (February 6-11, 2020), the study identified flow analogs with root-mean-squared differences (RMSD) below a specific threshold, indicating atmospheric circulation patterns that resemble that of the 2020 heatwave event. The distribution of 6-day mean Antarctic Peninsula T2m anomalies was then reconstructed from these analogs. The study also examined the contributions of different physical processes (horizontal temperature advection, adiabatic warming by subsidence, and diabatic heating) to the temperature changes using the thermodynamic equation. To determine the role of the Foehn effect, a mountain Froude number analysis was applied using ERA5 data. Finally, the influence of the Southern Annular Mode (SAM) was assessed by removing its trend and comparing the results to those obtained with the original data. Several sensitivity tests were performed to assess the robustness of results.

The 2020 summer was characterized by exceptional warmth across the Antarctic Peninsula, with the most extreme temperatures recorded between February 6-11, peaking at 18.3 °C at Esperanza Station on February 6th. The 6-day mean temperature anomaly over the Antarctic Peninsula was +4.5°C. The analysis of flow analogs revealed that similar atmospheric circulation patterns would have produced significantly warmer temperatures in the recent period (1985-2019) compared to the past (1950-1984). A 2020-like heatwave would be at least 0.4°C warmer in the recent period compared to the past, representing approximately a 25% increase. The probability of experiencing a 6-day mean temperature anomaly exceeding -2 °C has increased tenfold since the earlier period. The warm advection played a significant role in the rapid escalation of temperatures at the onset of the heatwave, with a secondary contribution from diabatic heating. The Foehn effect (leeward warming due to downslope winds) also contributed to the warming, particularly on the eastern side of the Peninsula. Analysis shows that the contribution of both warm advection and adiabatic warming increased significantly in the recent analogs compared to the past ones. In contrast to the initial expectation, the influence of long-term changes in the Southern Annular Mode (SAM) on the magnitude of the event turned out to be minor. After removing the SAM trend from the data, the difference between past and recent analog distributions remained substantial. Removing the regional mean temperature trend entirely from the dataset eliminated the difference between the two periods, indicating the primary role of long-term warming in exacerbating the heatwave.

The findings directly address the research question of climate change's role in the 2020 Antarctic Peninsula heatwave. The significant increase in the magnitude and probability of such events in the recent period strongly suggests a substantial contribution from long-term warming. The relatively minor role of the SAM trend, despite its known influence on Antarctic climate, highlights the dominant influence of thermodynamic changes associated with overall climate change in shaping the severity of this extreme event. This highlights the critical need to consider thermodynamic changes alongside dynamical aspects when assessing the impacts of climate change on extreme weather events. The study also reveals the contributions of warm advection and the Foehn effect to the heatwave's intensity, emphasizing the interplay of large-scale atmospheric dynamics and local topographic factors. The results have significant implications for understanding and predicting future extreme weather events in the Antarctic region, given the projected increase in the frequency and intensity of heatwaves under continued climate change.

This study provides robust evidence that long-term warming, rather than recent changes in atmospheric circulation patterns, is the primary driver of the amplified magnitude of the 2020 Antarctic Peninsula heatwave. The substantial increase in the probability and intensity of such events highlights the significant implications of climate change for the Antarctic region. Future research should focus on more detailed investigation of the complex interplay of large-scale atmospheric dynamics, regional feedbacks, and local processes like the Foehn effect in exacerbating extreme heat events. Further analysis using diverse datasets and attribution methods, along with more complex climate models, is crucial to refine our understanding of this phenomenon and its implications for the Antarctic ecosystem.

While this study provides strong evidence linking long-term warming to the 2020 heatwave, some limitations exist. The analog method relies on historical data and might not fully capture all aspects of climate change's influence. The study's analysis of the SAM's effect is limited to its summer trend; interannual variability and other factors beyond the summer SAM may influence the findings. The disentanglement of specific anthropogenic factors from the overall climate change signal is inherently complex. The relatively short record of Antarctic observations and significant interannual to decadal variability can also influence the study's analysis. Further research is needed to refine the understanding of the regional warming trends and their specific drivers, including potential roles for feedback mechanisms such as changes in water vapor and albedo.