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Global reinsurer Munich Re is looking back at the historic 2017 hurricane season as a harbinger of seasons to come, suggesting in a report that such high-cost cycles may become increasingly routine as climate change advances.
"Within a span of four weeks, the hurricane trio of Harvey, Irma and Maria made the 2017 hurricane season the costliest ever," said the Munich Re report. "Overall losses reached around US$215bn, according to preliminary estimates, and insured losses are expected to be around US$100bn."
Looking to understand why, the report noted that only a portion of the 2017 hurricane season was extremely active - the second half of August through early October.
"During this period, several meteorological preconditions for above-normal activity were met, such as sea surface temperatures in the tropical main development region substantially above average, very low levels of difference in winds at low levels and aloft, an active West African monsoon producing tropical cyclone seedlings, and - last but not least - sufficient moisture levels in the mid to upper troposphere," read the report.
With the conditions in place, the season "turned on", pumping out a cluster of extremely powerful storms, producing more major hurricanes in the span of a month than are usually produced on average every year - 3.4 per year being the norm since 1995.
"Besides the influences from natural multi-decadal climate variability such as warm and cold phases, climate change may also already have played a role, "although this cannot be attributed with any statistical significance," said Munich Re.
The German reinsurer said current projections of future conditions expect almost unchanged or stagnating overall tropical cyclone numbers in most ocean regions for the mid-21st and end-21st century. By contrast, the frequency of extreme storms (Cat 4-5) is projected to increase in most areas with continued climate change.
"Against the background of these projections, the 2017 season looks like a foretaste of the future," said the reinsurer. "Indeed, we suspect that the future projections of increased numbers of extreme storms may materialize in terms of a higher frequency of exceptional seasons such as 2004, 2005 and 2017."