First of all, why did you choose to undertake a study on the Indian monsoon?

Another example would be the Gulf Stream or the thermohaline circulation in the Atlantic (which has a big impact on global climate)as we call it.

Did you get the cue from or refer to any previous studies?

We have a climate department here at PIK (the Potsdam Institute) that is headed by Martin Claussen. He is one of the guys who pioneered studies in climate-vegetation interactions. For example they looked at the African monsoon and at the interaction of the monsoon there and the vegetation. We drew on this study about the African monsoon to develop our model of the Indian monsoon.

Was your study done entirely from Germany?

It is a very theoretical project. It's a sort of mathematical model which was rather simple. Our observational data was taken entirely from available books, studies and research data.

Would you say your study is an alarm bell for India?

What we showed was there is this possibility of failure of the Indian monsoon because of anthropogenic interferences: like emissions of particles because of forest clearance. We cannot really access the probability of this failure because we do not know how many aerosols will be emitted in the future. We do not know how land cover will change in South Asia in the next decade or so.

There is a need to do some sort of study to really explore the scenario: to assess what emissions will be in future, how land use will change then take more and more complex models and run this scenario. That would allow one to make some statement about the probability of the monsoon.

The study says the monsoon is in danger, but we have had floods in the western states of Gujarat and Maharashtra. Are you aware of that?

Of course, we are aware of this.

How do you explain that in the context of your study?

First of all we don't make any kind of prediction. We don't say, 'This is going to happen.' We say, 'This is a possibility.'

On top of air pollution you have increasing concentration of greenhouse gases. This means you increase carbon dioxide, methane and all this kind of gases in the atmosphere. This is called global warming, and it has the opposite effect on the monsoon in India.

If greenhouse gases increase then the monsoon also increases.

So there are two competing effects: on one hand it's weakening because of the aerosols on the other hand it's strengthening because of greenhouse gases. We are not in a position to say which one of these effects will dominate.

How drastically does the monsoon reduce when you cross the threshold?

It reduces very drastically. If the average rainfall from June to August is something like 8 mm per day all over India, it would go down to 1 mm per day if the threshold is crossed.

What would be your advice to Indian policy makers?

I would say every time humankind interferes with the environment, it can disrupt some kind of climate phenomenon. I would say try to control aerosol emissions, I would say try to control greenhouse gases. I would say formulate policy to reduce emissions of aerosols, stop cutting off forestland.

The march of development versus ecological balance has always been a gray area. How critical is the pollution's effect on the monsoon now?