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As 2023 proves to be another active year for hurricane activity and other catastrophe losses, modeling companies remain focused on long-term climate trends rather than annual variations.
Rising air and sea temperatures are more likely to have a lasting effect and are more closely scrutinized by modelers than temporary changes in weather patterns, but modeling companies are still making some adjustments to single out the short-term phenomena, experts say.
This year displays two opposing climate characteristics: warmer sea surface temperatures, which help foster hurricane activity, and El Nino conditions.
The 2023 hurricane season in the North Atlantic has seen these two competing aspects, which have opposing effects on hurricane activity.
“Sea surface temperatures in the tropical and subtropical Atlantic are at a record high this season, fueling hurricane activity with an increased amount of energy and moisture in the atmosphere,” said Elisabeth Viktor, senior natural catastrophe specialist at Swiss Re Ltd. in Zurich.
Meanwhile, El Nino conditions, which began in the summer and are expected to persist, can increase wind shear over the North Atlantic, inhibiting the formation of hurricanes, she said.
The hurricane season traditionally runs from June 1 to Nov. 30. In the most recent update to its well-respected hurricane forecast, Colorado State University said in August it expects 18 named storms this year, compared with an average of 14.4 from 1991 to 2020, and nine hurricanes, compared with the 7.2 average.
Meanwhile, worldwide insured natural catastrophe losses topped $100 billion in 2021 and 2022, according to Swiss Re.
Warmer sea temperatures are a continuing phenomenon and thus become accounted for in the inputs for catastrophe models, said Karen Clark, founder and CEO of Boston-Based catastrophe modeler Karen Clark & Co.
“The trends are very relevant,” Ms. Clark said. “The sea surface temperatures are trending, so that trend is incorporated into the model. Seasonal fluctuations are not as relevant,” she said.
Catastrophe modelers look at longer-term trends, said Peter Sousounis, Boston-based senior vice president and director of climate change research for Verisk Extreme Event Solutions, a unit of Verisk Analytics Inc.
“For example, we know we have high confidence that climate change is impacting certain aspects of extreme weather more than others. We believe that climate change is intensifying storms, and when those storms are more intense, they’re able to squeeze more moisture out of the atmosphere,” he said.
“Sea surface temperatures going up, hurricanes becoming more intense — that is accounted for in our model, that’s very important. The sea surface temperature being above or below average this particular year is not relevant to the modeling,” Ms. Clark said. “You get those random things once in a while, but it doesn’t necessarily mean that there are any trends or if there’s anything significant about it.”
The model that Verisk is currently developing, slated to be released in a few years, will give clients the ability “to extract those years in the model that are characterized by El Nino events,” Mr. Sousounis said.
Varying different parameters and atmospheric variables allows models to “produce all possible outcomes in accordance with their probabilities for a given year for insurers,” Ms. Clark said.
Swiss Re’s North Atlantic hurricane model is adjusted to account for the current period of higher hurricane activity compared with long-term history, Ms. Viktor said.
She added that the Atlantic hurricane season is not over yet, and tropical cyclones will have more opportunity to intensify than usual since sea surface temperatures are still well above average in the North Atlantic.
“It only takes one event to turn a season into a loss-intensive one, as Hurricane Ian demonstrated last year,” she said.