Rising sea levels making island nations such as Vanuatu more vulnerable to storms and amplifies the impact of tropical cyclones

Scientists say the devastation caused by Pam, the most powerful cyclone to hit the South Pacific since records began, was aggravated by climate change. However, the effect the changing climate is having on tropical storms remains largely unresolved.



The president of Vanuatu told a conference in Japan on Monday that climate change had contributed to Pam’s impact on his nation. There are reports that 90% of the buildings in the capital Port Vila have been destroyed or damaged after the cyclone hit over the weekend. Six people are reported to have been killed.

President Baldwin Lonsdale told delegates at a UN conference on disaster risk his people were being affected by more cyclones. He said this was a symptom of the climate crisis.

“We see the level of sea rise … The cyclone seasons, the warm, the rain, all this is affected ... This year we have more than in any year … Yes, climate change is contributing to this.”

Professor Richard Betts, head of climate impacts research at the Met Office Hadley Centre, said the human contribution to sea level rise over the past 100 years was well documented and makes island nations more vulnerable to storms and particularly storm surge.

“When cyclones and other storms occur, there is already a greater risk of coastal flooding because the background sea level has risen, largely due to human-induced global warming. How much more flooding has occurred due to human action is unclear, but ongoing sea level rise can be expected to further increase this risk unless coastal protection can be improved.”

Professor Myles Allen a climate scientist from the University of Oxford said while there is a suggestion cyclones may become more intense, the president’s assertion that climate change was causing more storms was not supported by science.

“It is a perfectly reasonable question for the president to be raising. Basic thermodynamics means that a warmer atmosphere, all other things being equal, makes more intense cyclones possible,” said Allen.

“But this does not mean cyclones have necessarily become more likely: indeed, the latest assessment of the UN Intergovernmental Panel on Climate Change stated explicitly that there is no clear evidence at present for any human-induced increase in tropic-wide cyclone frequency.

“On a personal level, I sympathise with the president’s evident frustration: he and the people of Vanuatu deserve an authoritative answer to the question of the role of past greenhouse gas emissions in cyclone Pam. The science isn’t there yet, but we are getting there.”

By March it would be normal for around four cyclones to have formed in the South Pacific. But, as Lonsdale said on Monday, the 2015 season has been particularly bad. Six cyclones have hit the region since the beginning of the year.

Dr Pete Inness, a tropical meteorologist from Reading University, said it was impossible make any inference from a single season.

“It is a very active year, but a single active year doesn’t in itself indicate a trend. There isn’t apparently a long term trend.”

In fact, he said, modelling expects cyclones in the South Pacific to shift southward and become 20-30% less frequent by the end of the century as a result of climate change.

“The things that control the number of cyclones are other things like the wind speeds at different levels in the atmosphere,” he said. “There’s really complicated changes projected to happen to the winds speeds in [the South Pacific], which, in concert to the changes in sea temperature, actually seem to indicate that we would expect fewer cyclones in this area in the next 50 to 100 years.”

Dr Chris Holloway, a tropical storm expert at the University of Reading, said that while the total number of storms may reduce, the number of very intense storms, like Pam, may increase slightly.

“Tropical cyclone Pam had the strongest winds of any South Pacific tropical cyclone on record, and is tied for having the strongest winds of any southern hemisphere tropical cyclone on record.

“Globally it is most likely that the total number of tropical cyclones will decrease with climate change while the number of the most intense storms, like Pam, will increase.”

Dr Ilan Kelman, reader in risk at University College London, said rising sea levels made it imperative that island states were supported in resilience building.

“We could have done much more to work with Vanuatu long before the cyclone struck in order to reduce the disaster potential. That is the point of this week’s disaster risk reduction conference in Japan. A cyclone alone does not create a disaster unless we are not ready for it,” he said.