Record-breaking sea temperatures across the Gulf of Mexico have been a key ingredient behind some of the intense hurricanes devastating the region this year.
Last month, Hurricane Helene made landfall on Florida’s “Big Bend” and then stalled over several states to the north dumping “enormous rainfall totals”, resulting in epic flooding which killed at least 220 people.
Just a couple of weeks later, Milton – the ninth hurricane to form in the Atlantic this year and one of the most rapidly intensifying hurricanes on record – has swept this week towards Florida’s Tampa Bay region, threatening communities that are still recovering from Helene’s impact.
A rapid attribution study recently concluded that record-breaking ocean temperatures in the Gulf of Mexico, which helped Hurricane Helene to “spin up”, were made 200-500 times more likely because of human-caused climate change.
Scientists tell Carbon Brief that the same intense ocean heat likely helped to fuel Milton’s behaviour and explains how hurricanes can become more intense in a fast warming world.
How do hot oceans fuel hurricanes?
A hurricane is the name for a tropical cyclone that forms in the Atlantic Ocean or northeastern Pacific Ocean.
Atlantic hurricanes typically first form over the tropical waters of the north Atlantic off the African continent. As the systems travel westwards across the Atlantic, they draw up the warm, moist air that rises from the surface of the ocean, using it to fuel themselves and grow stronger.
As the low-pressure system picks up energy, winds can begin to spin, forming a storm. The warmer the ocean water is, the more energy the storm accumulates and the more quickly it can intensify. Sea surface temperatures of more than 26.5C down to a depth of 50 metres can drive the storm to intensify into a hurricane, once wind speeds exceed 74 miles per hour.
The 2024 Atlantic season runs from the start of June to the end of November and has already seen multiple intense storms, including the powerful Helene and Milton hurricanes, which have struck Florida within just two weeks of each other.
Both hurricanes picked up energy as they travelled over the Gulf of Mexico, which is currently experiencing a marine heatwave.
The graph below shows the extra ocean heat content – a metric that captures the amount of thermal energy stored in the water – for the Gulf of Mexico. For each month, it shows the extra ocean heat, compared with the average amount for that month during 2013-23.
A tropical storm is said to undergo “rapid intensification” if its wind speed increases by at least 35mph over a 24-hour period. Hurricane Milton’s wind speed accelerated faster than all but two previously recorded storms, with more than a 90mph increase in speeds in just 24 hours, ranking it as one of the “strongest” Atlantic storms ever recorded.
A study published in August in the Nature journal Communications Earth & Environment examined hurricanes that form over the Gulf of Mexico. It found that “rapid intensification” is 50% more likely to occur during marine heatwaves.
A rapid attribution study by Climate Central indicates that, over the past two weeks, the record-breaking temperatures in the Gulf of Mexico were made 400-800 times more likely by climate change.
Dr Kevin Reed – a researcher from Stony Brook University in New York – tells Carbon Brief that “Hurricane Milton’s rapid intensification this week is a telltale sign of climate change, which is responsible – in part – for the near-record temperatures in the Gulf of Mexico currently”. He adds:
“Warmer ocean temperatures are leading to more storms that undergo rapid intensification leading to an increase in the proportion of storms that reach major hurricane strength.”
A rapid attribution study from the World Weather Attribution (WWA) service examining Hurricane Helene used a model to investigate its strong winds by analysing storms making landfall within two degrees (120 nautical miles) of Helene. It said:
“By statistically modelling storms in a 1.3C cooler climate, this model showed that climate change was responsible for an increase of about 150% in the number of such storms (now once every 53 years on average, up from every 130 years) and, equivalently, that the maximum wind speeds of similar storms are now about 6.1 m/s (around 11%) more intense.”
The same team is now conducting a rapid analysis on the influence of climate change on Hurricane Milton, which will be released on Friday.
“This is in line with other scientific findings that Atlantic tropical cyclones are becoming wetter under climate change and undergoing more rapid intensification,” the WWA study on Helene finds.
Dr Kerry Emanuel, a professor of meteorology at the Massachusetts Institute of Technology, tells Carbon Brief that “Milton’s behaviour is consistent with predictions that hurricane scientists have made going back at least three decades”.
New normal?
Since 1878, around six to seven hurricanes, on average, have formed in the North Atlantic every year, with only a couple typically making landfall in the US.
The number of Atlantic hurricanes on record has increased over the period 1851-2019. However, some research suggests that more consistent monitoring, rather than a true increase in hurricane numbers, is behind this trend.
There is a clearer trend of increasing hurricane intensity. Research shows that the proportion of tropical cyclones reaching at least category 3 intensity has also risen over the past four decades. Although the study does not confidently link this increase to climate change, it notes that higher sea surface temperatures are likely to contribute.
As Prof Andrew Dessler summarises on his Climate Brink blog, the impact of climate change on the intensity and frequency of tropical cyclones is still not certain. However, he says that “we can have high confidence that climate change will drive more intense hurricanes”.
Meanwhile, studies have shown that the record-breaking 2020 Atlantic hurricane season, when 14 hurricanes were recorded, was partly due to increased sea surface temperatures.
A study published by Nature Communications in 2022 found that human-caused climate change increased sea surface temperatures in the North Atlantic basin by 0.4-0.9C. The authors estimated that this increased “extreme three-hourly storm rainfall rates” and “extreme three-day accumulated rainfall amounts” for Atlantic storms by 11% and 8%, respectively.
Another 2022 study published in Nature Communications found that over the period 1982-2020, climate change-induced increases in sea surface temperatures doubled the probability of “extremely active tropical cyclone seasons”. The 2020 season might have been made twice as likely by ocean surface warming, the authors found.
The post Explainer: How hotter oceans can fuel more intense Atlantic hurricanes appeared first on Carbon Brief.
Explainer: How hotter oceans can fuel more intense Atlantic hurricanes
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Picture an American farm in your mind.
I fell flat on my backside one afternoon this January and, weirdly, it made me think of you. Okay, I know that takes a bit of unpacking—so let me go back and start at the beginning.
For the last six years, our family has joined with half a dozen others to spend a week or so up at Wangat Lodge, located on a 50-acre subtropical rainforest property around three hours north of Sydney. The accommodation is pretty basic, with no wifi coverage—so time in Wangat really revolves around the bush. You live by the rhythm of the sun and the rain, with the days punctuated by swimming in the river and walking through the forest.
An intrinsic part of Wangat is Dan, the owner and custodian of the place, and the guide on our walks. He talks about time, place, and care with great enthusiasm, but always tenderly and never with sanctimony. “There is no such thing as ‘the same walk’”, is one of Dan’s refrains, because the way he sees it “every day, there is change in the world around you” of plants, animals, water and weather. Dan speaks of Wangat with such evident love, but not covetousness; it is a lightness which includes gentle consciousness that his own obligations arise only because of the historic dispossession of others. He inspires because of how he is.
One of the highlights this year was a river walk with Dan, during which we paddled or waded through most of the route, with only occasional scrambles up the bank. Sometimes the only sensible option is to swim. Among the life around us, we notice large numbers of tadpoles in the water, which is clean enough to drink. Our own tadpoles, the kids in the group, delight in the expedition. I overhear one of the youngest children declaring that she’s having ‘one of the best days ever’. Dan looks content. Part of his mission is to reintroduce children to nature, so that the soles of their feet may learn from the uneven ground, and their muscles from the cool of the water.
These moments are for thankfulness in the life that lives.
It is at the very end of the walk when I overbalance and fall on my arse—and am reminded of the eternal truth that rocks are hard. As I gingerly get up, my youngest daughter looks at me, caught between amusement and concern, and asks me if I’m okay.
I have to think before answering, because yes, physically I’m fine. But I feel too, an underlying sense of discomfort; it is that omnipresent pressure of existential awareness about the scale of suffering and ecological damage now at large in the world, made so much more immediately acute after Bondi; the dissonance that such horrors can somehow exist simultaneously with this small group being alive and happy in this place, on this earth-kissed afternoon.
How is it okay, to be “okay”? What is it to live with conscience in Wangat? Those of us who still have access to time, space, safety and high levels of volition on this planet carry this duality all the time, as our gift and obligation. It is not an easy thing to make sense of; but for me, it speaks to the question of ‘why Greenpeace’? Because the moral and strategic mission-focus of campaigning provides a principled basis for how each of us can bridge that interminable gulf.
The essence of campaigning is to make the world’s state of crisis legible and actionable, by isolating systemic threats to which we can rise and respond credibly, with resources allocated to activity in accordance with strategy. To be part of Greenpeace, whether as an activist, volunteer supporter or staff member, is to find a home for your worries for the world in confidence and faith that together we have the power to do something about it. Together we meet the confusion of the moment with the light of shared purpose and the confidence of direction.
So, it was as I was getting back up again from my tumble and considering my daughter’s question that I thought of you—with gratitude, and with love–-because we cross this bridge all the time, together, everyday; to face the present and the future.
‘Yes, my love’, I say to my daughter, smiling as I get to my feet, “I’m okay”. And I close my eyes and think of a world in which the fires are out, and everywhere, all tadpoles have the conditions of flourishing to be able to grow peacefully into frogs.
Thank you for being a part of Greenpeace.
With love,
David
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