Ocean warming fuelled by human-made climate change has intensified all hurricanes in the Atlantic this year, new research has shown.

Published Wednesday, the study concluded that higher-than-usual ocean temperatures boosted the intensity of all eleven storms recorded between June and November, increasing their highest sustained wind speeds by 9 to 28 mph (14.5 to 45 km/h). This resulted in seven hurricanes reaching a higher category on the Saffir-Simpson Hurricane Scale and two tropical storms – Debby and Oscar – strengthening into hurricanes.

The Saffir-Simpson wind scale is the most widely recognized risk assessment method for hurricanes. Developed in 1971 by civil engineer Herbert Saffir and meteorologist Robert Simpson and introduced to the general public in 1973, the scale classifies hurricanes into five categories based on their sustained winds. To be classified as a hurricane, a storm must have a one-minute-average maximum sustained winds of at least 74 mph or 119 km/h (Category 1). Currently, the highest classification is assigned to storms with winds blowing at a speed of at least 157 mph or 252 km/h (Category 5).

The scale also estimates the extent of potential damage to properties, infrastructure, and livelihoods, with Categories 3-5 hurricanes – also known as major hurricanes – expected to cause “devastating” to “catastrophic” damage and loss due to the strength of their winds. However, the scale does not take potentially deadly hazards such as storm surge, rainfall flooding, and tornadoes into account.

A Flourish table

Ocean warming made major hurricanes like Helene (Category 4) and Milton (Category 5), which killed at least 260 people, were made 16 mph and 24 mph stronger, respectively.

Warming Oceans

Hurricanes form when warm ocean waters heat the air above them, causing the warm, moist air to rise. As this air ascends, it cools and condenses, forming clouds and creating a low-pressure zone beneath. This low pressure allows more air to rush in from surrounding areas. As the system continues to develop, it can lead to the formation of thunderstorms. If there are no strong winds to disrupt the process, the storm can intensify and evolve into a hurricane, or typhoon, depending on its location.

Though tropical cyclones are a rather common weather phenomenon, there has been a significant increase in their intensity in recent decades, which scientific observations link to anthropogenic climate change. These abnormal trends are attributed largely to rising ocean temperatures, which have been abnormally high for more than a year.

Over most of the global oceans, the first ten months of 2024 had record-warm sea surface temperatures, according to the National Oceanic and Atmospheric Administration (NOAA).

"When the climate increases in temperatures, when the atmosphere gets wetter, conditions are more conducive, allowing hurricanes to have a higher speed limit," explained Daniel Gilford, a climate scientist at Climate Central, the non-profit news organization behind the study.

"That means that these hurricanes can spin faster in a warmer and wetter world."

The study reflects the National Oceanic and Atmospheric Administration's (NOAA) forecast that the 2024 Atlantic hurricane season would likely be “above-normal” owing to near-record ocean heat and La Niña conditions.

Ongoing Trend

The Climate Central analysis is based on new-peer-reviewed research published in Environmental Research: Climate on Wednesday.

30 of the 38 storms occurring between 2019 and 2023 that the attribution study looked at intensified into a higher category on the Saffir-Simpson Scale because of ocean warming. The study concluded that hurricanes in the past five years "were 8.3 mph (13.4 km/h) faster, on average, than they would have been in a world without climate change."

Attribution studies quantify climate change’s influence on an individual weather event, often in the immediate aftermath of a heatwave, storm, or flood. Often, these scientific analyses highlight how much more rare it would be for such an event to occur in “a world without climate change.”

According to Climate Central, human-made climate change made elevated sea surface temperatures in the tracks of 2024 Atlantic hurricanes up to 800 times more likely.