Explainer: How Climate Change Is Fueling Hurricanes

By Gloria Dickie

(Reuters) - Storm Debby made landfall in Florida's Big Bend region on Monday as a Category 1 hurricane, part of what U.S. government forecasters have predicted could be an extraordinarily busy 2024 Atlantic hurricane season.

Debby, the fourth named storm of the season, was expected to bring days of torrential rain and catastrophic flooding across the U.S. Southeast. Last year, Hurricane Idalia, which briefly gained Category 4 strength, also struck the Big Bend region, causing billions of dollars in damages.

Scientists say climate change is helping to fuel stronger, more destructive hurricanes. Here is how:

IS CLIMATE CHANGE AFFECTING HURRICANES?

Yes, climate change is making hurricanes wetter, windier and altogether more intense. There is also evidence that it is causing storms to travel more slowly, meaning they can dump more water in one place.

If it were not for oceans, the planet would be much hotter due to climate change. But in the last 40 years, the ocean has absorbed about 90% of the warming caused by heat-trapping greenhouse gas emissions. Much of this ocean heat is contained near the water's surface. This additional heat can fuel a storm's intensity and power stronger winds.

Climate change can also boost the amount of rainfall delivered by a storm. Because a warmer atmosphere can also hold more moisture, water vapor builds up until clouds break, sending down heavy rain.

During the 2020 Atlantic hurricane season — one of the most active on record — climate change boosted hourly rainfall rates in hurricane-force storms by 8%-11%, according to an April 2022 study in the journal Nature Communications.

The world has already warmed 1.1 degrees Celsius above the preindustrial average. Scientists at the U.S. National Oceanic and Atmospheric Administration (NOAA) expect that, at 2C of warming, hurricane wind speeds could increase by up to 10%.

NOAA also projects the proportion of hurricanes that reach the most intense levels — Category 4 or 5 — could rise by about 10% this century. To date, less than a fifth of storms have reached this intensity since 1851.

HOW ELSE IS CLIMATE CHANGE AFFECTING STORMS?

The typical "season" for hurricanes is shifting, as climate warming creates conditions conducive to storms in more months of the year. And hurricanes are making landfall in regions far outside the historic norm.

In the U.S., Florida sees the most hurricanes make landfall, with more than 120 direct hits since 1851, according to NOAA. In recent years, however, some storms are reaching peak intensity and making landfall farther north than in the past.

This trend is worrying for mid-latitude cities such as New York, Boston, Beijing, and Tokyo, where "infrastructure is not prepared" for such storms, said atmospheric scientist Allison Wing at Florida State University.

Hurricane Sandy, though only a Category 1 storm, was the fourth costliest U.S. hurricane on record, causing $81 billion in losses when it hit the Northeastern Seaboard in 2012.

As for timing, hurricane activity is common for North America from June through November, peaking in September – after a summertime buildup of warm water conditions.

However, the first named storms to make U.S. landfall now do so more than three weeks earlier than they did in 1900, nudging the start of the season into May, according to a study published in August in Nature Communications.

Hurricane Beryl, which formed in the Atlantic in June, was the earliest Category 5 storm on record.

The same trend appears to be playing out in Asia's Bay of Bengal where, since 2013, cyclones have been forming earlier than usual - in April and May - ahead of the summer monsoon, according to a November 2021 study in Scientific Reports.

HOW DO HURRICANES FORM?

Hurricanes need two main ingredients — warm ocean water and moist, humid air. When warm seawater evaporates, its heat energy is transferred to the atmosphere. This fuels the storm's winds to strengthen. Without it, hurricanes cannot intensify and will fizzle out.

CYCLONE, TYPHOON, HURRICANE - WHAT'S THE DIFFERENCE?

While technically the same phenomenon, these big storms get different names depending on where and how they were formed.

Storms that form over the Atlantic Ocean or central and eastern North Pacific are called "hurricanes" when their wind speeds reach at least 74 mph (119 kph). Up to that point, they are known as "tropical storms."

In East Asia, violent, swirling storms that form over the Northwest Pacific are called "typhoons", while "cyclones" emerge over the Indian Ocean and South Pacific.

(Reporting by Gloria Dickie in London; Additional reporting by Joseph Ax; Editing by Marguerita Choy and Christina Fincher)