Hurricane Melissa is being fuelled by exceptional ocean heat

Jamaica is being directly hit by what may be the strongest hurricane on record to make landfall in the Atlantic Ocean, forecast to produce up to a metre (40 inches) of rain over its mountains – and there is virtually no doubt that global warming has made Hurricane Melissa as strong as it is.

The warm waters that fuelled its intensification were 500 to 700 times more likely as a result of climate change, according to initial estimates by Daniel Gilford and his colleagues at Climate Central, a US non-profit organisation.

“The ‘500 to 700 times more likely’ number is big,” says Gilford. “It really illustrates how unlikely the extremely warm temperatures we are observing around Melissa would be without human-caused climate change.”

Tropical cyclones like Melissa are powered by warm water. The warmer the sea surface, the more water vapour forms as storms move over them. As moist, warm air rises, the water vapour starts to condense out, releasing latent heat. This warms the air and makes it rise higher, leading to more condensation and so on. This is the energy source that powers tropical cyclones.

In the central Caribbean where Melissa rapidly intensified to a Category 5 hurricane, sea surface temperatures are 1.4°C (2.5°F) higher than is typical for October. These abnormal temperatures also extend to an unusual depth, so there is a huge amount of extra heat energy in these waters.

This means that as Melissa churns up the sea and brings deeper waters to the surface, sea surface temperatures are remaining high. Where there is only a shallow layer of warm water, by contrast, colder waters are brought to the surface, cutting off a storm’s energy supply.

“There has been a perfect storm of conditions leading to the colossal strength of Hurricane Melissa: a warm ocean which has fuelled its rapid intensification over the last few days, but it is also moving slowly, meaning more rain can fall whilst it moves across land,” Leanne Archer at the University of Bristol, UK, said in a statement. “Most of these conditions have been supercharged by the extra heat in our oceans and atmosphere due to climate change.”

The combination of high winds and extreme rainfall could lead to catastrophic damage in Jamaica. Three people have already died preparing for the storm, which is expected to make landfall around 11am or 12pm local time.

“This is one of those worst-case scenarios,” Hannah Cloke at the University of Reading, UK, said in a statement. “The whole country will have a deep and permanent scar from this beast of a storm. It will be a long and exhausting recovery for those affected.”

Studies of previous disasters have shown that events such as this can reduce economic growth for decades afterwards. It had been suggested by economists that there can be rapid recovery, or even extra growth stimulated by recovery efforts, but these ideas have mostly turned out to be wrong.