Poll: Your view on climate change

Climate change is worsening the impacts of hurricanes such as Irma and Harvey, experts warned.

Extreme weather such as Irma, a category 5 hurricane and one of the strongest ever seen in the Atlantic, could occur without global warming, the University of Reading's tropical weather specialist Chris Holloway said.

But impacts of human-induced climate change that the world is already seeing, including rising sea levels and warmer temperatures which cause more rainfall, are worsening the risks of hurricanes, he said.

Dr Holloway said: "Climate change increases the risks of some of the impacts of hurricanes. You could have a storm like Irma without climate change - there are on record similar storms, not very many."

But he said: "Sea level rise has been going up because of climate change, we know that with a large degree of certainty.

"Any storm surge pushed onshore by high winds is happening at a higher base level.

"Where the sea is higher you're going to increase the risk of dangerous coastal flooding.

"Similarly, rainfall is another large danger of these kind of storms. Harvey sat over Texas for days and most of the danger was fresh water flooding due to heavy rainfall."

The risk of heavy rainfall is always there with a storm, but warmer temperatures allow the atmosphere to hold more water vapour, leading to more rainfall, Dr Holloway added.

"We've got more rain on top of what we would have without climate change," he said.

"These two risks, sea flood water and fresh water flooding, are the ones that cause the most fatalities."

He also said the science indicated the world was likely to see more intense hurricanes because of climate change, and they could shift where they form so that places currently at risk may be slightly less under threat, while other areas could be more at risk.

Dr Dann Mitchell, from the University of Bristol's Cabot Institute, said: "The question of whether climate change 'caused' any particular weather event is the wrong one; instead, we must probe how climate change alters extreme weather.

"Aside from the warming atmosphere, rising sea level and surface ocean warming have likely contributed to the impact of both Irma and Harvey."

Prof Kevin Horsburgh of the National Oceanography Centre added: "Whereas specific hurricanes are not caused by climate change, they may be worsened by higher surface heat content in the tropics, which provides the driving force for hurricanes."