Climate change: new hurricanes, force 6 – 02/10/2024 – Marcelo Leite

Climate change: new hurricanes, force 6 – 02/10/2024 – Marcelo Leite

One of the strongest winds ever to occur in Brazil reached 168.8 km/h. It was in Siderópolis (SC), from June 30th to July 1st, 2020, a bomb cyclone that left 13 people dead.

The wind speed, if it was measured at 10 m above the ground for at least 1 minute, would qualify the storm as a force 2 hurricane (154 to 177 km/h) on the Saffir-Simpson tropical cyclone intensity scale.

In addition to Atlantic hurricanes, this class of storms also includes Pacific typhoons. The 168.8 km/h pales in comparison to the 315 km/h (force 5) of super typhoon Hayan, which in November 2013 claimed more than 7,000 victims in the Philippines and caused damage of more than US$13 billion (R$65 billion) .

The scale was created in 1971 by engineer Herbert Saffir and meteorologist Herbert Simpson. Initially it included criteria such as precipitation magnitudes and sea surge, but ended up being based exclusively on wind strength.

Force 5, the highest intensity range, starts at 252 km/h, well below what was observed in Cyclone Hayan. It has been debated for some time whether the climate crisis is requiring the inclusion of a category 6, a proposal that came up again on Monday (5) in an article in the scientific journal PNAS, from the US Academy of Sciences.

Researchers Michael Wehner and James Kossin not only propose force 6 but also stipulate, based on statistical calculations, that it starts at 309 km/h. By this criterion, only five cyclones would fall into the hypothetical category – and all of them occurred in the last decade in the Pacific Ocean (not to be lost due to the name).

This concentration in recent times suggests that this is an intensification of typhoons driven by climate change. The strength of these cyclones is directly related to the temperature at the sea surface, their fuel, and it increases with global warming.

If only the maximum category of force 5 is maintained, the historical record since 1980 indicates a total of 197 storms with such intensity. And half of them happened in the last 17 years, report Wehner and Kossin, including Atlantic hurricanes.

Your argument in favor of scaling up has to do with communicating risk and harm. They feel that, by having a final category with no upper limit, Saffir-Simpson does not give due public visibility to devastating cyclones that are likely to become more frequent.

In fact, this is a common prediction in models that project the future of the climate. Cyclones are titanic engines that transfer heat from the ocean to the upper atmosphere, producing banks of clouds and circular winds with diameters of up to 500 km; the warmer the waters, the more powerful they tend to become.

The Paris Agreement (2015) established that atmospheric warming should not reach 2ºC and, preferably, remain at 1.5ºC above the pre-industrial era, to prevent an increase in the frequency and intensity of extreme events such as cyclones, wildfires, deadly heatwaves, droughts and floods.

Sound familiar? The year 2023 was the hottest on record, and 2024 could even break that record.

The last 12 months, for the first time in history, had an average temperature of 1.5ºC above the Paris safety threshold. But it will take a few more years at this level to conclude that there is no reversal in sight.

Some climate projections indicate that, if the atmosphere warms by 2ºC by the middle of this century, an increasingly plausible trajectory, the probability of new category 6 hurricanes in the Gulf of Mexico will double.

Hurricane Katrina, which killed almost 2,000 people in 2005, only reached strength 5 at sea (280 km/h) and 3 when it hit the coast of New Orleans. Maria, which devastated Puerto Rico in 2017 with force 4, had almost 3,000 deaths.

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