Why are hurricanes becoming more intense in the wake of Milton and Helene?

Alberto, Beryl, Chris, Debby, Ernesto, Francine, Gordon, Helene, Isaac, Joyce, Kirk, Leslie, Milton and, potentially in a couple of weeks, Nadine.

These are the names of every tropical cyclone that has ripped through the Atlantic Ocean this hurricane season alone, a number that has surprised – and worried – experts.

Hurricane Milton ploughed into Florida’s Gulf Coast last night, tearing trees, ripping roofs and killing several people in a retirement home.

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Milton, after flinging out tornadoes causing even more damage, is now moving out to sea. Flash flood warnings are in place as Milton’s storm surge – the rise in water generated by strong winds pushing ocean water ashore – swells.

The soaking rains and lashing 85mph winds of Milton have come only weeks after Helene – and forecasters say Nadine could be on her way, too.

But why are hurricanes becoming more intense?

What is a hurricane?

Hurricanes are a type of tropical cyclone, circular storms that form over warm waters, with low air pressure at the centre and winds greater than 74mph.

These cyclones are only called hurricanes, however, if they form in the North Atlantic, the northeastern Pacific, the Caribbean Sea or the Gulf of Mexico.

If these storms develop in the northwest Pacific, they’re classified as typhoons.

They also have different names if they form down in the  Southern Hemisphere: a tropical cyclone for the southern Indian Ocean or the South Pacific and a cyclone in the northern Indian Ocean.

What causes hurricanes?

Atlantic hurricanes can usually be traced back to Africa, according to the National Oceanic and Atmospheric Administration. Westward winds crash into warm ocean waters and the temperature difference between the air and the sea powers storms.

Inside the chaotic storm, moisture evaporates and rises, sucking up all the new swirling warm air over and over again, while the Earth’s rotation helps keep them spinning.

How does climate change affect hurricanes?

Hurricanes, like all parts of nature, aren’t inherently bad. These violent storms help regulate the world’s climate by shoving heat away from the tropics. They’ve always been around too, so scientists don’t tend to say that climate change is ‘causing’ more hurricanes.

But temperatures are rising because the burning of fossil fuels spews greenhouse gases into the atmosphere, helping trap heat near the planet’s surface – the ocean included.

Every degree Celsius of warming, meanwhile, allows the air to hold about 7% more water.

‘The extra heat in the oceans and seas in particular, caused by the greenhouse effect mainly care of fossil fuel emissions, is simply adding extra energy into our weather systems,’ Jim N R Dale, a meteorologist with the British Weather Services, an independent forecasting service, explains to Metro.

‘Which means “normal” weather events are being ramped up by that extra energy. Until we reduce CO2 and methane emissions the world can expect to experience more and more hazardous and sometimes catastrophic events.’

Feverish oceans ramp up every part of the hurricane-forming process, Dr Fredi Otto, lead of the World Weather Attribution, an international group of scientists and meteorologists, tells Metro.

‘High ocean temperatures mean hurricanes can form in the first place, but also the higher the temperature the more moisture the hurricane picks up, thus increasing the rainfall intensity,’ she says.

‘If the high sea temperatures are combined with high humidity and lower vertical wind sheer, a measure called potential intensity, hurricanes are also more intense with respect to the wind speed.’

Has climate change made Hurricane Milton stronger?

Dr Otto, who is also a senior lecturer in climate science at Imperial College London, says this isn’t actually the right question to ask.

‘The question in this case would need to be the other way round,’ she explains. ‘There is nothing that suggests Milton was not made more likely and more intense by our burning of fossil fuels.’

The unusually warm sea surface temperature around Milton’s path is up to 800 times more likely because of climate change, the nonprofit Climate Central has found.

A raft of recent storms have all been strengthened by the planet’s thermostat being cranked up. Compared to preindustrial times, storms can sometimes be twice more likely to form now, the World Weather Attribution found.

‘Across the board, rainfall from these events was amplified by anthropogenic climate change: Katrina in 2005 by 4%, Irma in 2017 by 6%, Maria in 2017 by 9%, Florence in 2018 by 5%, Dorian in 2019 by 5-18% Ian in 2022 by 18% and Harvey in 2017 by 7-38%,’ explains Dr Otto.

Helene too, the World Weather Attribution found, warning that the hurricane is the kind that the US should come to expect as the world burns coal, oil and gas for energy.

‘Milton,’ Dr Otto adds, ‘will not be different.’

Are hurricanes becoming more frequent?

While hurricanes are roaring at a strength rarely seen before, they’re not actually any more frequent than usual. Most models show either no change or a decrease in hurricane frequency even as burning fossil fuels and releasing greenhouse gases for centuries have increased global temperatures.

What are the worst hurricanes on record?

The Great Hurricane of 1780 got its name for a reason. Blasting its way through the Caribbean islands, the storm killed more than 22,000 people.

Mitch is the second-deadliest hurricane on record, with a death toll of 11,000 in Honduras. The Galveston Hurricane of 1900 may, in fact, have killed 1,000 more people, with the most conservative estimate putting it at 6,000 people.

You often hear hurricanes being referred to as a ‘Category X hurricane’. This is the Saffir-Simpson Hurricane Scale, which classes storms based on wind speeds.

A Category 1 hurricane, for example, whips up winds between 74 and 95mph. Compare this to a Category 5, which is anything above 157mph. Milton is now a Category 2, but storms can leap by several categories overnight.

For the most part, scientists agree that climate change will mean longer, more active hurricane seasons. So we might have to revise this scale.

‘Rainfall will be more intense, windspeeds will be more intense, therefore there will be more destruction,’ says Dr Otto. ‘Scientists argue we need a new category 6 or possibly 7, so people can prepare adequately.’

Dale would agree. Storms that suddenly intensify in wind speed just before landfall were relatively rare between 1976 and 2005 – by the end of the 21st century, these destructive hurricanes might occur every five or so years.

‘I now fear we are acting too late to stop such events; safety and survival should be becoming more and more paramount in our thoughts going forward,’ says Dale.

‘Meanwhile, manmade climate denial goes against indisputable science, it’s dangerous.’

Does the UK get hurricanes?

In short, no. The sea around the UK is far too tepid for heat-hungry hurricanes to form, the Met Office says.

Though, Britain can be pounded by the remains of hurricanes as they drift across the Atlantic, becoming ‘ex-hurricanes’.

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