Attributing an Antarctic heatwave event to climate change

An anthropogenic climate change signal can be detected in specific events in Antarctica.
Published in Earth & Environment
Attributing an Antarctic heatwave event to climate change
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On 7th February 2020, all the front pages of scientific news bulletins opened with the news that the temperature record in Antarctica had been broken. They were referring to the 18.3 ºC that reached at the Esperanza station in the previous day. Three days later, they echoed again that this time Antarctica had exceeded 20 ºC in Seymour Island. Although the latter was finally refuted by a WMO commission (Rocha et al., 2021), a media debate was opened on whether these values were a consequence of climate change. As the person in charge of the data and climate of the Spanish Antarctic meteorological stations managed by the Spanish Meteorological Service (AEMET), I also had this concern, especially because our station Gabriel de Castilla (Figure 1) in Deception Island had also broken its temperature record. At that moment, I thought that getting a robust answer on the role played by climate change in  the heatwave  would not be easy. Meteorological measurements in Antarctica are not as long as in other continents and temperatures have large interannual fluctuations. Both characteristics implicate that  temperature trends can differ substantially  over different regions of the continent due to the regional effects of the Southern Annular Oscillation.

Figure 1.  Photography of Gabriel de Castilla Station in Deception Island  courtesy of José Vicente Albero  (left). Temperature evolution at Gabriel de Castilla Station from 1 to 15 February 2020 (right). Data of the Spanish stations can be consulted at https://antartida.aemet.es/ 

A few days after the event, the latest issue of the special report of the Bulletin of the American Meteorological Society entitled "Explaining Extreme Events from a Climate Perspective" landed on my desk. Inside, there was an article that used an interesting methodology to attribute an event of extreme temperatures in the Iberian Peninsula based on circulation analogs. To use this method, it was necessary for the event to have a high dynamic component, as in this case, which was associated with a strong ridge over the Antarctic Peninsula (Xu et al., 2021). Therefore, the potential role of climate change in this event was likely to be addressed using this method. During the confinement of 2020 caused by the COVID19 pandemy, I began to program the methodology. At that time, I contacted David Barriopedro to understand some details of the methodology. However, I ended up in a bottleneck when I realized that the data I was using from the ERA5 reanalysis published up to that point was not sufficiently long. Data only went back to 1979 and the analog methodology required longer data series. Therefore, in the middle of 2020 I decided to put the project on hold until the expected ERA5 back extension came out.

Figure 2. Highest temperatures recorded during the 6-11 February 2020 heatwave. Highest 3-hourly temperature and date for the available stations of the Antarctic Peninsula and the 6-11 February 2020 period according the SYNOP messages. Figure from Gonzalez-Herrero et al. (2022)

It was not until 2021 that I resumed the project with ERA5 and formed a team to analyze and interpret the data. After verifying that the ERA5 data were valid prior to 1979, we analyzed the singularity of the heat wave that affected the Antarctic Peninsula in 2020. Among other things, we observed that the event was characterized by a relatively long heat wave of 6 days (Figure 2) and that record-breaking temperature at Esperanza did not correspond to the warmest day at the regional scale. After analyzing the circulation analogs, we found that regional warming exacerbated the magnitude of the heatwave event. To be sure of this result, we performed multiple sensitivity tests slightly changing parameters such as the areas, the threshold values, etc. in order to show that the results were robust to the methodological choices. I estimate that I may have recalculated the methodology around 50 times, fortunately always obtaining  similar results.

In the published article, we show that the temperature anomaly during the heatwave was amplified by circa 25% by climate change. However, the specific physical processes still need to be explored in detail. The use of regional climate models can fill this gap and be useful to better understand how temperature is amplified during heat wave events. In any case, the main message that should reach the science community, but also the general population is that climate change is already noticeable in specific events in a continent as isolated as Antarctica.

 

References

Rocha FM, Schaefer C, Skansi M de LM, Colwell S, Bromwich DH, Jones P, King JC, Lazzara M, Renwick J, Solomon S, Brunet M, Cerveny RS. 2021. WMO Evaluation of Two Extreme High Temperatures Occurring in February 2020 for the Antarctic Peninsula Region. Bulletin of the American Meteorological Society. American Meteorological Society, 1(aop): 1–20. https://doi.org/10.1175/BAMS-D-21-0040.1.

Xu M, Yu L, Liang K, Vihma T, Bozkurt D, Hu X, Yang Q. 2021. Dominant role of vertical air flows in the unprecedented warming on the Antarctic Peninsula in February 2020. Communications Earth & Environment. 2(1): 1–9. https://doi.org/10.1038/s43247-021-00203-w.

González-Herrero, S., Barriopedro, D., Trigo, R.M. et al. Climate warming amplified the 2020 record-breaking heatwave in the Antarctic Peninsula. Commun Earth Environ 3, 122 (2022). https://doi.org/10.1038/s43247-022-00450-5

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