India’s monsoon and Surrey’s green fields

I got back from a couple of workshops in Princeton in America yesterday. They included a talk by an author of this paper on how we appear to be changing the summer rainfall  that India relies on to grow the crops to feed its billion people. On my doormat I found an election flyer by the Guildford’s save the greenbelt party. There is an election in the UK the week after next. They want to stop house building on green fields in the Guildford area. I don’t doubt their sincerity, and green fields are something we all enjoy. But when you read about the changes in rainfall that crops required by a billion people, this does look a bit parochial.

The paper is a bit out of my field but I think the point they make is as follows. They study not CO2 emissions but that of tiny particles produced by for example burning of fuels. These particles are called aerosols, and the point is that although bigger particles quickly fall to ground, tiny ones can get carried up into the atmosphere and cross continents and oceans. These particles affect cloud formation and hence rainfall.

They study this in huge computer models. Essentially they run the model with the aerosols we emit and see approximately the drop in rainfall India has seen recently, i.e., their models that incorporate the aerosols we emit agree with what we have seen. Then they take the aerosols we emit out of the model, run it again, and see significantly greater rainfall in summer in the north-east of India.

As it happens most of change appears to be due to aerosols produced in south-east Asia itself, not in Europe or elsewhere. But it is a reminder that we should move on from debating whether or not climate change is real, it is, and determine as accurately as possible what we are doing to our climate. And that when we vote, as we all should, we should worry about more than local fields.

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