Why this winter will be world's warmest on record?

The year 2023 has been marked by climatic extremes, with intense heatwaves during the summer and autumn months that have set off global alarm bells. As winter approaches, there is growing speculation about the possibility of experiencing the warmest winter on record.

The latest research published in the journal Advances in Atmospheric Sciences forecasts the development of a moderate to strong Eastern Pacific El Niño during the upcoming northern hemisphere winter, with an ENSO index exceeding 1.5°C. This phenomenon is expected to induce unusual anticyclone activity in the Northwest Pacific, which will lead to the formation of a Pacific-North American atmospheric teleconnection wave pattern. This pattern is likely to have a significant impact on the winter climates of East Asia and North America.

The unprecedented heat experienced throughout 2023 has led to widespread concern about the potential for a historically warm winter season. The global average temperature from June to October 2023 was 0.57℃ above the 1991-2020 average, with August and September temperatures exceeding historical averages by 0.62℃ and 0.69℃, respectively, surpassing the records set in 2016.

The return of the El Niño phenomenon after seven years has exacerbated the warming trend, contributing to the breaking of historical temperature records. This has intensified interest in the winter climate predictions for 2023/24.

In light of these developments, the Short-Term Climate Prediction Team at the Institute of Atmospheric Physics, Chinese Academy of Sciences, undertook a comprehensive analysis. Leveraging their self-developed climate prediction systems, the team investigated the anomalies in the global climate for the upcoming 2023/24 winter season. The findings of this research are eagerly awaited as they will provide insights into the expected winter climate trends.

How warm will this winter truly be?

The report underscores the synergistic effects of the El Niño phenomenon and the ongoing global warming trend. It suggests that the mid-low latitudes of Eurasia and most regions in the Americas are poised for an unusually warm winter season.

There is a high probability, estimated at 95%, that the global average surface temperature for the 2023/24 winter will surpass all previous records. In China, surface temperatures could potentially be more than double the norm, potentially marking the highest winter temperatures recorded since 1991.

Climate prediction involves not only grasping the internal variability of the climate system but also accounting for external influences. For example, the back-to-back La Niña events from 2020 to 2022 had a cooling effect, delaying the progression of global warming and underscoring the impact of external forces.

Recent studies from the United States have also highlighted the role of external forces, particularly pointing to the 2019 Australian wildfires as a catalyst for consecutive La Niña events. The proposed mechanism involves aerosols from the wildfires generating low clouds over the Southern Ocean, which leads to cooler sea surface temperatures, a northward shift of the Intertropical Convergence Zone, and a predisposition for multi-year La Niña conditions.

While the influence of such external forces is still a subject of debate due to the limited number of occurrences, historical data from volcanic eruptions provides additional evidence. Research by the Sun Yat-sen University Volcanic Research Team suggests that over the last thousand years, eruptions of 26 volcanoes in the Southern Hemisphere were often followed by three-year periods of La Niña, supporting the theory that cooling in the Southern Ocean can induce multi-year La Niña events.

Projecting 2023/24 winter temperatures

The Short-Term Climate Prediction Team at the Institute of Atmospheric Physics, Chinese Academy of Sciences, has employed sophisticated climate prediction systems to project the climate trends for the winter of 2023/24. Their analysis suggests the development of a moderate to strong Eastern Pacific El Niño, which is expected to significantly affect the winter climates of East Asia and North America.

The research highlights the combined influence of the El Niño event and the ongoing trend of global warming. It indicates that regions in the mid-low latitudes of Eurasia and most parts of the Americas are likely to face an exceptionally warm winter, with a 95% chance of surpassing previous temperature records.

In China, the forecasted surface temperatures could be more than double the usual, potentially setting a new record for the highest winter temperatures since 1991.

Understanding the climate system requires consideration of both internal variability and external forcings. The consecutive La Niña events from 2020 to 2022, which temporarily slowed global warming, emphasize the importance of external factors. The 2019 Australian wildfires, for example, have been associated with triggering multi-year La Niñas due to the aerosols they produced, which formed low clouds over the Southern Ocean and led to cooler sea surface temperatures, thereby promoting La Niña conditions.

Research by Zhou & Liu (2023) from Sun Yat-sen University supports this, showing that historical volcanic eruptions in the Southern Hemisphere often resulted in multi-year La Niña events, confirming the impact of cooling in the Southern Ocean on global climate patterns.

As we prepare for the winter of 2023/24, these climatic elements combine to suggest a potentially historic warm winter. This situation highlights the complex relationship between natural phenomena and human-induced climate change, underscoring the need for ongoing research and proactive action to confront the escalating climate crisis.

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