Climate: more intense cyclones because of global warming

AFP

AFP

Wednesday, September 6, 2017 09:40

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Wednesday, September 6, 2017 09:57

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PARIS | cyclones as Irma, who was hit Wednesday, the Caribbean, feeding on the energy released by the oceans: as a result, scientists predict that the intensity of these events, which are also called hurricanes or typhoons, is increasing but not their frequency across the globe.

Twentieth century

Lack of satellite data at the global scale before 1970, it is not possible to say how tropical cyclone activity has evolved in the Twentieth century. Prior to the establishment of a satellite-based surveillance complete, cyclones even very intense could have passed unnoticed if they had not touched the land, for example. The reduced number of tropical cyclones also contributes to the weakness of the statistical data and makes their operations more difficult.

In the north Atlantic, for twenty years, an increase in the frequency of cyclones has been noted but the opposite was true between 1970 and 1995, according to Franck Roux, of the University Paul Sabatier of Toulouse, france.

In fact, the researchers found that the cyclonic activity in this region follows the cycles of several decades and feel that it is not yet possible to say whether the rise in this region is a natural variability or climate change.

In the Pacific northwest, there has been a slight decrease in hurricane activity between 1980 and 2010.

Twenty-first century

Computer models simulating climate are strengthening the intensity of cyclones (wind and rain) and a possible decrease in their frequency level of the globe in the future.

“Cyclones of an intensity greater are the expected consequences of climate change,” explains Valérie Masson-Delmotte, member of the IPCC, reference group at the global level on climate.

“The higher the temperature of the water and the humidity are, the higher the cyclone can take the intensity. However, these two elements are more intense due to the increase of the” greenhouse effect”, explains the scientist. “We consider that there are 7% of humidity in the atmosphere per degree of warming”, she says.

“Climate change does not create these storms, but it emphasizes their impact,” says Anders Levermann of the Potsdam Institute for Climate Impact Research.

Sea-level rise: a dual effect

The increase in the level of the oceans is one of the markers of the warming of the planet. The increase varies according to the regions of the globe, has been by an average of 20 cm in the Twentieth century and could reach up to almost a metre by 2100.

However, the cyclones also produce a swell that generates the “tidal storm”. The two combined effects will contribute to further expose constructions and coastal populations.

Movement of cyclones

Studies show, according to Météo France, that “the latitude at which the cyclones reached their maximum intensity has moved toward the poles (closer to the coastal areas of N. D. L. R) in the course of the past 35 years in both hemispheres”.

This could be linked to the expansion of the tropical belt, that is to say, areas of both sides of the Equator where reign a warm and humid climate.

“Places that are more accustomed and better prepared for cyclones could be less exposed and other, less well prepared, could be more,” says James Kossin of the us Agency for oceanic and atmospheric (NOAA).