Bad weather in 2023, particularly severe convective storms, drove an average combined ratio for American homeowners’ insurers to 111 per cent, leading to credit rating downgrades for dozens of companies.

Gallagher Re says the first half of 2024 became the second costliest on record for US SCS, and such an intense start to the Atlantic hurricane season brings fresh concerns for the rest of the year.

The active start for natural catastrophes in the first half of 2024 pushed global insured losses 25 per cent above the H1 decadal average to at least $61 billion, with the vast majority of losses attributed to US severe convective storms, according to Gallagher Re’s H1 2024.

Yet, a report from Karen Clark & Co observes that some climate change statements are not supported by the evidence. Ms Clark is the pioneer catastrophe modeller heading KCC.

The July document said: “It is incorrect to attribute the seemingly increasing losses to climate change because to date, there is no scientific consensus on trends in SCS frequency or severity due to warming temperatures.

“Scientists who have been investigating climate impacts for the past few decades, including the Intergovernmental Panel on Climate Change, have found no conclusive trends other than a possible shift in the centre of SCS activity from Tornado Alley to the Southeast.”

The report 2023 Severe Convective Storm Season: How Extreme Was It and Why? said there were 19 SCS events last year that each exceeded $1 billion in losses.

The report highlighted how population growth and construction cost inflation have increased SCS losses.

“Building construction costs have increased significantly over the past ten years and the average cost to build a single-family home has nearly doubled,” KCC said.

“But once exposures are normalised to current values, there is no trend.”

SCS losses exhibit a high degree of interannual variability, particularly at a regional scale, although not as much as hurricanes.

KCC said many factors influence weather patterns and their severity, including the El Niño-Southern Oscillation – a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean.

“Regional hotspots occur due to the confluence of atmospheric ingredients and large-scale weather systems steered by the jet stream across specific areas of the US,” the white paper stated.

America’s SCS season was marked by persistent atmospheric patterns that supported repetitive SCS activity over the Midwest and Southeast during the spring and summer months.

Hot and humid air overspread the region in the spring, fuelled by above-average Gulf of Mexico sea surface temperatures. The jet stream was stronger than average, particularly the southern portion of the jet stream, due to the ongoing El Niño.

Last year’s jet stream remained stronger than normal.

In only three months, nine events caused insured losses exceeding $1 billion and two events caused losses exceeding $3 billion, according to the KCC SCS model.

One of the most destructive wind-dominant events happened on March 29 when a significant tornado outbreak developed in Iowa and Missouri before progressing into Wisconsin, Illinois and eventually Indiana, generating numerous tornadoes along the way.

Hundreds reported damaging wind gusts during this major spring SCS event and more than $3 billion in insured losses, according to the KCC SCS Model.

In mid-June, a stationary front positioned over the Southeast acted as a thunderstorm initiator, day after day, bringing repeated bouts of severe weather to the region.

Much damage occurred from the amount of large hail that the storms produced, some of it 5.9in in diameter in Sanger, Texas. The weeklong weather event resulted in over 1,500 hail reports and nearly $6 billion in insured losses.

There were over 600 reports of damaging wind gusts during this major spring SCS event and more than $3 billion in insured losses, according to the KCC SCS model.

However, KCC said that while the active 2023 season led to above-average insured losses, the losses were not extreme.

“A recurrence of 2017 or 2011 would result in higher losses,” the KCC white paper stated. “Future active seasons could easily lead to losses well above those of 2023, and we are likely to see such losses again within the next five years.”