Global warming may hit monsoon

Last Updated 06 November 2012, 19:38 IST

Global warming could cause frequent and severe failures of the Indian summer monsoon in the next two centuries, a new research suggests.

Using sophisticated computer simulation, European researchers showed a reduction of monsoon rainfall between 40-70 per cent below the normal levels over the next 200 years.

Compared against observational records maintained by the Indian Meteorological Department since 1870s, the failures were unprecedented.

The immediate effects of climate change on monsoon rainfall have already been observed by other researchers. However, the patterns of response in the coming decades are not uniform across different models and studies.

Published in the journal “Environmental Research Letters” on Tuesday, the new study found that monsoon failure would be much more frequent in future with the warming trend whereas monsoon failure was very rare under pre-industrial conditions.

The researchers at Potsdam Institute for Climate Impact Research and Potsdam University claimed increasing temperatures and a change in strength of the Pacific Walker circulation in spring could cause more frequent and severe changes in monsoon rainfall.

The Walker circulation usually brings areas of high pressure to the western Indian Ocean but, in years when El Nino occurs, this pattern gets shifted eastward, bringing high pressure over Indian land mass and suppressing the monsoon, especially in spring when the monsoon begins to develop.

Their simulations showed as temperatures increase in the future, the Walker circulation, on average, brings more high pressure over India, even though the occurrence of El Nino doesn’t increase.

Climatic shifts

“Our study points to the possibility of even more severe changes to monsoon rainfall caused by climatic shifts that may take place later this century and beyond,” said Jacob Schewe, lead author of the study.

Studies have illustrated that in spite of the rise in atmospheric carbon dioxide concentration of about 70 parts per million by volume and in global temperatures of about 0.5 degree Celsius over the last six decades, the All India Rainfall index does not yet show the expected increase in rainfall.

The reviewers, Andrew Turner at the University of Reading and H Annamalai at the University of Hawaii, gave several reasons for why the region’s observed rainfall has not yet increased. Among them are inconsistent rainfall observations, decadal variability of the monsoon, the effects of aerosols resulting from industrialisation, and land-use changes.

But regional projections for devastating droughts and floods are still beyond the reach of current climate models, according to the reviewers’ analyses.

(Published 06 November 2012, 05:38 IST)

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