German climate researchers issue India warning

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Man's murder of monsoon

- German climate researchers issue India warning

G.S. MUDUR

 

New Delhi, Aug. 17: Increasing air pollution and loss of forest cover

in South Asia may trigger a sudden breakdown of the Indian monsoon

and sharply reduce rainfall in the subcontinent within decades,

climate scientists said.

 

Researchers at Germany's Potsdam Institute for Climate Impact

Research who set out to explore the stability of the summer monsoon

over India have discovered that it's particularly vulnerable to human

influences.

 

"The stage seems to be set for a man-made reduction of the Indian

summer monsoon," climate physicist Kirsten Zickfeld and her

colleagues said in a paper published in the latest issue of the

journal, Geophysical Research Letters.

 

The scientists have shown that tiny particles called aerosols, spewed

into the atmosphere during the burning of coal and firewood, reduce

monsoon rainfall, while rising greenhouse gases such as carbon

dioxide tend to increase rainfall.

 

A steady rise in aerosols will reduce the amount of sunlight striking

land and lower land temperatures. This will decrease the supply of

moisture-laden air from the sea and lower rainfall. Shrinking forest

cover will also have the same effect.

 

"When these effects exceed a critical threshold, the monsoon could

experience a sudden breakdown," Zeckfeld told The Telegraph in a

telephone interview. "We'd then see a very weak monsoon consistently

over many years," she said.

 

"This is something we should be concerned about," said Sourendra

Bhattacharya, a climate scientist at the Physical Research Laboratory

in Ahmedabad.

 

Climate records have revealed that the Indian monsoon has undergone

abrupt changes over the past 8,000 years. "There have been some

dramatic ups and downs in the monsoon," said Bhattacharya who

specialises in ancient climate studies.

 

"While those ancient changes in rainfall were driven by natural

phenomena, we're now anticipating changes influenced by human

activities," he said.

 

Zeckfeld said her study could not quantify the reduction in the

rainfall, nor predict when exactly the breakdown of the monsoon might

occur.

 

But with rising aerosol levels, it could happen over the next few

decades, she said.

 

If India adopts new technologies to reduce its aerosol emissions,

Zeckfeld said, the monsoon may display a "roller-coaster" behaviour.

After a suppression over the next decades, as aerosol-reduction

policies begin to take effect and economic growth drives up carbon

dioxide emissions, the monsoon may abruptly intensify and re-

establish the "wet-monsoon" regime within a few years.

 

"It might be hard for India to have the monsoon doing really weird

things — reducing and then abruptly increasing," she said. The study

has also cautioned that India might find it a challenge to adapt to

such a roller-coaster scenario.

 

This is not the first study to signal the danger that aerosols pose

to the monsoon. A study by climate scientist Murari Lal, formerly at

the Indian Institute of Technology, New Delhi, in 1995 was the first

to show that aerosols can weaken rainfall.

 

Bhattacharya said the impact of aerosols would depend on what type

they were. Some aerosols such as soot absorb sunlight and will tend

to increase rainfall, while sulphur-containing particles will reflect

sunlight and tend to reduce rainfall.

 

"We might also have a scenario where the effects of aerosols and

greenhouse gases cancel each other out," Bhattacharya said.

 

http://www.telegraphindia.com/1050818/asp/frontpage/story_5126863.asp