Sea surface temperatures not the only driver of tropical cyclone activity
The natural climate oscillation El Niño-Southern Oscillation (ENSO) in the Pacific also has a major influence on global tropical cyclone activity. Hurricane activity in the North Atlantic tends to be reduced during El Niño phases, while a higher-than-average number of severe typhoons typically develop in the Northwest Pacific under the same conditions. This pattern is reversed during La Niña phases.
For 2021, forecasts up to now expect the ENSO status to remain in the neutral range over the summer months, but with the possibility of a shift towards La Niña conditions around the end of the season. Thus, unlike under El Niño conditions, the development of hurricanes will not be inhibited across the western Atlantic Basin. In combination with the expected warm sea surface temperatures, this indicates that a relatively active hurricane season is likely. However, it is not possible to make a reliable prediction of how many of the storms will make landfall, or where they might come ashore.
Early predictions indicate above-average season
In comparison: The long-term average (1950–2020) of tropical cyclones per season in the North Atlantic is 11.7. Of these, an average of 6.4 reach hurricane strength, of which 2.8 reach major hurricane intensity.
The storm activity expected for 2021 is above the long-term average, but corresponds roughly to the average values for the current active phase in the Atlantic, with a greater number of storms observed since the mid-1990s. During this period, a cyclical warming of sea surface temperatures in the North Atlantic favours the development of more storms. Additional warming of ocean temperatures is also occurring due to climate change, slowly providing even more fuel for these storms.
Last year saw a record 30 tropical cyclones in the North Atlantic under La Niña conditions with extremely high sea surface temperatures. Of these, 14 reached hurricane strength. Despite the large number of storms, losses remained within reasonable limits: overall losses in North America amounted to some US$ 43bn, of which US$ 26bn was insured. The most destructive hurricane season, in 2017, saw overall losses more than five times as high.
For the typhoon season in the Northwest Pacific, neutral ENSO conditions means that cyclone activity should be near the long-term average between 1980 and 2020 (26 named storms, 16 typhoons, 9 super typhoons).
Torsten Jeworrek, Member of the Board of Management, commented as follows: “In future, while climate change may not increase the overall number of tropical cyclones, research findings indicate that it will increase the number of particularly severe storms. And, of course, it is these storms that cause the greatest losses, so prevention is critical. As insurers, we continue to develop our expertise to allow us to shoulder as much as possible of the financial risks from such weather extremes on behalf of individuals and society as a whole.”