Climate change makes cyclones more intense, destructive — scientists

PARIS, France (AFP) – Climate change does not make cyclones, such as that battering Bangladesh, more frequent but it does render them more intense and destructive, according to climatologists and weather experts.

These immensely powerful natural phenomena have different labels according to the region they hit, but cyclones, hurricanes and typhoons are all violent tropical storms that can generate 10 times as much energy as the Hiroshima atomic bomb.

They are divided into different categories according to their maximum sustained wind strength and the scale of damage they can potentially inflict.

“A cyclone is a low-pressure system that forms in the tropics in an area hot enough for it to develop,” Emmanuel Cloppet, from French weather office Meteo France, told AFP.

“It is characterized by rain/storm clouds that start rotating and generate intense rains and winds, and a storm surge created by the wind,” he added.

These huge weather phenomena – several hundreds of kilometers (miles) across – are made more dangerous by their ability to travel huge distances.

Tropical cyclones are categorized according to wind intensity, rising from tropical depression (under 63 kilometers per hour), through tropical storm (63-117 kph) to major hurricane (above that).

They are termed cyclones in the Indian Ocean and South Pacific, hurricanes in the North Atlantic and Northeast Pacific, and typhoons in the Northwest Pacific.

Meteorological agencies monitoring them use different scales to categorize them, depending on the oceanic basin in which they occur.

The most well-known scale for measuring their intensity and destructive potential is the five-level Saffir-Simpson wind scale.

“The overall number of tropical cyclones per year has not changed globally but climate change has increased the occurrence of the most intense and destructive storms,” according to the World Weather Attribution (WWA), a group of climate scientists and climate impact specialists whose goal is to demonstrate reliable links between global heating and certain weather phenomena.

The most violent cyclones – categories three to five on the Saffir-Simpson scale – that cause the most destruction have become more frequent, the WWA said.

Climate change caused by human activity influences tropical cyclones in three major ways – by warming the air and oceans and by triggering a rise in sea levels.

“Tropical cyclones are the most extreme rainfall events on the planet,” the WWA said in its publication “Reporting Extreme Weather and Climate Change.”

Since the atmosphere is warmer, it can hold more water, so when it rains it pours.

“A rise in air temperature of three degrees Celsius can potentially produce a 20 percent increase in the quantity of rain generated by a cyclonic event,” said Cloppet.

It is these intense torrential downpours that lead to sometimes fatal floods and mudslides, as was the case of Cyclone Freddy, which killed hundreds of people in Malawi and Mozambique earlier this year.

Climate change is also warming the oceans. This warm water fuels cyclones and gives them their strength.