How much of a role did climate change play with Hurricane Melissa?

Millions of people crosswise the caribbean sea ar trying to sell with the devastating personal effects of Hurricane Melissa, which tore through the region this week.

Like so many storms of late, Melissa underwent a rapid intensification, defined as when a storm’s maximum sustained wind speed increases by 51 km/h over 24 hours.

Melissa strengthened by 112 km/h over that same period, making it a case of what some are calling extreme rapid intensification.

As we continue to burn fossil fuels, pumping CO2 into the atmosphere, the planet continues to warm, causing myriad changes in weather patterns and the overall climate.

So what was climate change’s role with Hurricane Melissa?

Scientists are getting better at analyzing the effects of climate change on severe weather events, like droughts, floods and hurricanes.

There are several organizations doing their own analyses, including Environment and Climate Change Canada.

One of these organizations — which includes climate scientists from around the world — is ClimaMeter. It did a rapid attribution analysis of Hurricane Melissa and found that both climate change and natural variability played a role.

It found that hurricanes similar to Melissa are roughly 10 per cent wetter and 10 per cent windier than in the past due to our changing climate. Natural variability played a role in its formation and path.

One of the main ways in which climate change plays a role is in the change in our oceans. Temperatures have been historically warmer than normal, and that warm water acts as the fuel for hurricanes. The warmer the water, the more fuel.

Shel Winkley, a meteorologist with Climate Central, a group of independent scientists who report on climate change, said the temperature in the Caribbean Sea is anywhere from 1.4 C to 2 C warmer than average.

“We know that those water temperatures are made anywhere from 500 to 700 times more likely to be that warm at this time of the year in this part of the Caribbean due to the excess heat that we as humans have put into the atmosphere that then sinks into the ocean,” Winkley said.

This in turn can contribute to rapid intensification, as it has with four of the five hurricanes that have formed in the Atlantic Basin.

“This is something that we didn't see a couple of decades ago but that we're now seeing at least every season, if not even multiple times [a] season,” Winkley said.

Another independent analysis was done by Imperial College London’s Grantham Institute, which focuses on climate change and the environment.

Using its Imperial College Storm Model (IRIS), the analysis found that climate change increased Melissa’s wind speed by roughly seven per cent, or 18 km/h.

Inside the eye of Hurricane Melissa

While many people focus on the rapid intensification of hurricanes, Ralf Toumi, director of the Grantham Institute and co-author of the analysis, said that’s not necessarily what we should be focusing on.

“People talk about the rapid intensification. I think ... That's fair enough, but it actually happened days before the landfall … it rapidly intensified to Category 4 over 24 hours,” he said.

“The other intensification was that as it approached the island, it really became something altogether more nasty because it became essentially a Category 6 ... But we don't have this category because folklore says that anything over a five causes the same amount of damage, basically complete damage. So there's no need to.”

The analysis also concluded that this type of hurricane event was four times more likely compared with pre-industrial times.

“We think it's like pre-industrial before the warming happened, it would have been maybe one in 8,000-year return,” Toumi said. “Even now [it] would be like a 1,000-year, 2,000-year event. So even now it's extremely unlikely, but then [the] headline figure that it's basically become four times more likely."

As for the destruction, the authors found that without climate change, a weaker hurricane would have been about 12 per cent less damaging. (They did not focus on damage estimates, as it is too soon to tell what that number will be.)

While the numbers may vary between the rapid attribution groups due to their methodology, the message is still the same: Climate change is altering hurricanes.

As we pump more fossil fuels into our atmosphere, the oceans — which absorb more than 90 per cent of excess heat trapped by greenhouse gases — will continue to warm, and hurricanes will continue their destruction.

"But you can't adapt to a Category 5. It will cost you a fortune. Basically, you can't build for that sort of resilience. So there are limits to adaptation."

Senior Science Reporter

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