Air pollution and forest clearance endanger Indian monsoon

15 August 2005

Increasing air pollution and forest conversion in South Asia could lead to a failure of the Indian summer monsoon. This has been shown by researchers at the Potsdam Institute for Climate Impact Research (PIK) in a study exploring the stability of the Indian monsoon. The results of the study appeared in the current issue of "Geophysical Research Letters".

The recurrent monsoon rains have a profound impact on the lives of people in India. A weak summer monsoon is frequently accompanied by poor harvests and food shortages among the rural population, which constitutes two thirds of India's total population. Monsoon precipitation which is stronger than usual can similarly have devastating consequences, as the catastrophic rainfalls of recent weeks in Mumbai (Bombay) have demonstrated.

In the current PIK study, researchers discovered a mechanism which could lead to a failure of the Indian summer monsoon: increasing air pollution with airborne particles ("aerosols") over India - caused by fires and the consumption of fossil fuels - as well as forest clearance, could lead to a regional increase of the Earth's brightness ("planetary albedo"). Thereby less sunlight reaches the surface, causing the temperature over land to decrease. The supply of moist air which feeds the monsoon rains ceases and precipitation decreases dramatically.

The likelyhood of such a breakdown of the Indian summer monsoon cannot be inferred from the study. For this, analyses will be needed which consider realistic projections (so-called "scenarios") of the air pollution as well as of land-use change in South Asia. Also, a further effect would have to be considered: rising concentrations of greenhouse gases. The latter have an opposite effect on the summer monsoon: more greenhouse gases in the atmosphere lead to a temperature increase over land and thus to stronger precipitation. At present it is still not possible to determine which one of these two effects will ultimately dominate.

The Potsdam Institute for Climate Impact Research (PIK) was founded in 1992 and employs about 110 scientists. Its research on climate change, climate impacts and sustainable development is of international renown. PIK is a member of the Leibniz Association.

Original article:
Zickfeld, K., B. Knopf, V. Petoukhov, and H. J. Schellnhuber (2005), Is the Indian summer monsoon stable against global change?, Geophysical Research Letters, 32, L15707, doi: 10.1029/2005GL022771

Dr. Kirsten Zickfeld, e-mail, phone +49 331 288-2518

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