Extreme storms: how climate change is fueling hurricanes

From Hurricane Helene to Hurricane Yagi, severe storms are lashing the world, and scientists warn that a warming planet is increasing its destructive power to unprecedented levels.

Here’s what the latest research reveals about how climate change is fueling tropical cyclones — a common term for both climates.

– More punches –

First, the basics: warm ocean surfaces produce more water vapor, providing additional energy to storms, which strengthens their winds. Warmer conditions also allow them to hold more water, increasing rainfall.

“On average, the destructive potential of hurricanes has increased by about 40 percent due to the 1 degree Celsius (about 2 Fahrenheit) warming that has already occurred,” Michael Mann, a climatologist at the University of Pennsylvania, told AFP.

In a recent paper in the Proceedings of the National Academy of Sciences (PNAS), Mann added his voice to calling for the Saffir-Simpson scale to be expanded to include a “new class of superstorm” — Category 6, where sustained winds. exceeding 192 miles per hour (308 km per hour).

According to experts, climate change set the stage for Helene, which peaked as a Category 4 hurricane.

“Ocean temperatures were at record levels, fueling the potential for a storm like this to strengthen and become a very large and destructive storm,” David Zierden, a Florida state meteorologist, told AFP.

– Increasing speed –

A “surge,” defined as a hurricane that increases in speed by 30 knots within a 24-hour period, is also becoming more common.

“If intensification occurs very close to the coast towards fall, it can have a big impact, which you saw last week in the case of Helene,” said Karthik Balaguru, a climate scientist at the Pacific Northwest National Energy Laboratory. , he told AFP.

Balaguru was the lead author on a paper this year in the journal Earth’s Future that used decades of satellite data to show “a dramatic increase in the rates at which storms increased near the coast, and this is around the world.”

The explanation is twofold.

Warm weather systems reduce wind shear — changes in wind speed and direction and height — along the Atlantic Coast of North America and the Pacific Coast of Asia.

“When you have strong wind shear, you tend to tear up the core of the storm,” explained Balaguru.

Climate change is also causing more moisture along the coast compared to the open ocean.

This is likely due to a thermal gradient created when land heats faster than water, causing changes in pressure and wind circulation that push moisture into the middle troposphere where storms can reach it. More data are needed to confirm this hypothesis.

Additionally, rising sea levels — about a foot over the last century — means hurricanes are now operating from higher elevations, increasing storm surges, Zierden said.

– How many times? –

Although the impact of climate change on how often hurricanes occur is still an active area of ​​research, studies show that it may increase or decrease frequency, depending on the region.

Particulate pollution from factories, automobiles, and the energy industry blocks sunlight, partially offsetting the warming effects of greenhouse gases.

In a Science Advances paper, Hiroyuki Murakami, a physicist at the National Oceanic and Atmospheric Administration, found that particulate emissions from the United States and Europe peaked around 1980, and their decline led to an increase in the speed of hurricanes in the Atlantic. .

Conversely, in Asia, high pollution levels in China and India could suppress the occasional storm in the western Pacific, Murakami told AFP.

Another study he led found that human activity has increased typhoon activity along Japan’s coast, increasing the risk of rare rainfall events in the west of the country through rain fronts—even when the storms themselves may not make landfall.

This year’s North Atlantic hurricane season was initially expected to be very strong. However, various weather factors created a lull from August to September, according to Zierden and Murakami.

Now, though “we’ve seen a big change in the last week,” Mann said. With the hurricane season continuing until November 30, we are not clear yet, he emphasized.

this/jgc