Climate change: more intense cyclones, but not more frequent

AFP

AFP

Sunday, 27 August, 2017 04:32

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Sunday, 27 August, 2017 04:32

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The intensity of cyclones as Harvey, who was hit Saturday in Texas and caused catastrophic floods in the future could be enhanced by increasing the temperature of the planet, but these events should not be more frequent, say scientists.

20th century: uncertainties

Lack of satellite data at the global scale before 1970, it is not possible to say how tropical cyclone activity has evolved in the 20th 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. Where the weakness of the statistical data and the prudence of scientists.

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 in 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 increase in the number of cyclones in the 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.

21st century: more intensity

The computer models simulating the climate of the 21st century indicate a possible strengthening of the intensity of cyclones (wind and rain) and a possible decrease in their frequency level of the globe.

“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.

Sea levels: higher and higher

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.

To a displacement of the cyclones?

Studies show, according to Météo France, that “the latitude at which the cyclones reached their maximum intensity has shifted toward the poles over 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.

The shift of cyclonic activity in the north Atlantic could, according to Météo-France, to make the Caribbean sea and the gulf of Mexico, “a more peaceful, to the detriment of the east coast of the United States,” but this trend needs to be confirmed by other studies.