India’s ‘dry’ monsoon caused by air pollution

  

Indian air pollution has been blamed for its dry monsoon season, but a scientist has revealed that European pollution may also play a part in it.

The volume of the summer monsoon has been weakening since the 1950s.

And Yi Ming of Princeton University in New Jersey claimed his experimental models suggest that the effect of European aerosol pollution accounts for about half the drop in the volume of monsoon rainfall – the other half is down to pollution over south Asia.

“The summer monsoon provides up to 80 per cent of total annual rainfall in south Asia, and supports 20 per cent of the world’s population,” New Scientist quoted Ming as saying.

With his colleagues, Ming used climate models to assess how different factors changed the monsoon.

The monsoon is brought by large-scale wind patterns that transport heat between the northern and southern hemispheres.

For half the year the northern hemisphere experiences more solar heating and so is warmer than the southern hemisphere; the situation is reversed during the other six months.

As the winds head north over the Indian Ocean during the northern hemisphere's summer they pick up moisture, which falls as rain over south Asia.

Air pollution in the form of aerosols can weaken these long-distance wind patterns, however.

That’s because it reflects sunlight back into space, cooling the polluted area.

Thick aerosol pollution over Europe in summer ensures that the northern hemisphere isn’t much warmer than the southern hemisphere, so there is nothing to drive the winds – and nothing to trigger the monsoon.

In as-yet-unpublished experiments, he confirmed the important

role that the European pollution plays in weakening the monsoon.