Research press release


Nature Climate Change

Climate change: Decline in tropical cyclones during the twentieth century

20世紀の熱帯低気圧の年間発生数は、19世紀後半と比べて約13%減少したことを報告する論文が、Nature Climate Change に掲載される。


今回、Savin Chandたちは、過去の記録とモデルデータを用いて、1850年以降の熱帯低気圧の年間発生数が、全球スケールと地域スケールの両方で減少傾向にあることを明らかにした。20世紀中の全球的な熱帯低気圧の発生数は、1850〜1900年と比較して、約13%減少した。熱帯低気圧が形成される海盆の大部分で、この減少は1950年以降加速しており、その主たる原因が熱帯の大気循環の弱化だったという見解をChandたちは示している。この減少傾向が唯一当てはまらないのが北大西洋海盆で、ここ数十年間は熱帯低気圧の発生数が増加している。その原因について、Chandたちは、20世紀後半になって、北大西洋海盆での人為的エアロゾル排出量が減少したために、熱帯低気圧の発生数が増加傾向に転じたという仮説を示しているが、それでも産業革命以前の時代と比べれば、熱帯低気圧の年間発生数は少ないと述べている。


The annual number of tropical cyclones decreased by approximately 13% during the twentieth century, compared with the late nineteenth century, according to a study published in Nature Climate Change.

It is not clear how tropical cyclones change under human emissions because a warming ocean is expected to intensify storms, while some changes in atmospheric circulation are thought to prevent storm formation. Providing historical context is challenging, as the observational record is not complete, especially before 1950. This has led to conflicting assessments of past tropical cyclone trends.

Using historical records and model data, Savin Chand and colleagues reveal declining trends in the annual number of tropical cyclones since 1850 at both global and regional scales. The global annual number of storms decreased by approximately 13% in the twentieth century compared with the period between 1850 and 1900. For most tropical cyclone basins, this decline has accelerated since the 1950s, which the authors suggest is mainly the result of a weakening of tropical atmospheric circulation. The only exception to this trend is the North Atlantic basin, where the number of tropical cyclones has increased over recent decades. The authors suggest that this may be because the basin is recovering from a decline in tropical cyclone number due to human-related aerosol emissions in the late twentieth century. The number of annual storms is still, however, lower than in pre-industrial times, they state.

These findings support studies that suggest that current climate change leads to a decrease in the number of tropical cyclones. It should be noted, however, that frequency is only one aspect controlling the risks associated with tropical cyclones, as the intensity and geographical location are also expected to change. As these factors were not assessed herein, no direct conclusions on the overall changes in risk can be derived.

doi: 10.1038/s41558-022-01388-4


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