Greenland's melting may deregulate the Asian monsoon

in Planète & EnvironnementCrédits : NASA / NOAA.

Pardamien Altendorf, scientific editor

If the Asian monsoon were to be deregulated in the decades to come, the origin could well be in the massive liberation of fresh water in the north of the Atlantic by the cast iron of Greenland.Indeed, researchers have recently demonstrated how the disruptions initiated in the North Atlantic Basin have led in the past to a reorganization of rain diets in Southeast Asia.The results were published in the journal Nature Geoscience this November 18.

The Asian monsoon conveys the freshwater essential to more than a billion people between south-eastern China and Bangladesh, passing by India.This planetary wind system is organized by the temperature contrast that appears each summer between a continental mass overheated in the north and a relatively fresh ocean in the south.

Despite the distance between them, the Asian monsoon is modulated by the ocean currents of the Atlantic basin.We are talking about Amoc (ATLANTIC RESIDional Orturning Traffic) to summarize this circulation which carries a large amount of heat from the tropics to the pole.Also, any change in its intensity tends to affect the areas of monsoons and to increase or decrease the amount of rain falling on a given region.

Study the past to better anticipate the future

However, with climate change, it is precisely expected that the Amoc weakens, which would necessarily have an influence on the evolution of monsoons regimes.However, at present, the precise relationship which links the two systems remains poorly known.To better understand, a group of researchers has decided to seek answers in the past of the earth.

The period chosen by scientists targets the exit of the penultimate glaciation, there are 147,000 to 125,000 years ago, at a time when many iceberg debahs weakened or even collapsed the amoc.Thanks to the study of stalagmites in southwest China and an innovative methodology allowing to decouple the influence of the temperature from those of precipitation, the authors of the study could see as the monsoon behaved when theAmoc undergoing diet reductions.

"In continental climates, there is nothing better than stalagmites as climatic archives because they offer an incomparably high dating clarification on several millennia," notes Hubert Vonhof, principal author of paper.

A graduated response from the Asian monsoon to the decreases of the Amoc

The results of this work show that for low disturbances, that is to say for a slightly slowed Atlantic circulation, the Asian monsoon lasts a little less, but does not show a major change in the rain diet.Conversely, for significant disruptions with a collapse of the Amoc, the monsoon is sharply reduced due to the weakening of the thermal contrast between the continent and the ocean linked to the fall of heat transport to the pole byOceanic currents.

"The study decrypts with unprecedented details how Mousson's climates reacted to the impulses of cast iron water at that time," said Hubert Vonhof."We have made a big step forward to better understand the global consequences of climate change induced by today's man".