Latest research on climate change and the Indian monsoon. An interview with Prof. Levermann (PIK)

You and your colleagues have recently published a scientific paper on “Basic mechanism for abrupt monsoon transitions”. Could you briefly outline your findings of the study?

We find that every monsoon system bears the potential for an abrupt shut-down. That is because the basic dynamics of a monsoon circulation is based on a self-amplification which strengthens the monsoon in spring and keeps it going during the rainy season. If significantly disturbed, this might lead to a spiraling down of the circulation and result in strongly reduced rain fall. Such disturbance could be natural but also human land use change and air pollution could trigger an abrupt transition. Climate records from the past have shown strong variations in monsoon rainfall. Fortunately, back then there were no or few people around that could have suffered from such an abrupt change. If it was to occur in the future that would be different. However, the abrupt transition of a monsoon system is not a likely future evolution. It is a risk that needs to be taken into account when considering land use and air pollution.

The Indian monsoon is seen as one of the tipping points of the global climate system. Could you specify what kind of threats the Indian monsoon is facing due to global warming?

Generally global warming increases monsoon circulations. That is very roughly due to the more rapid warming over land than over the ocean. Region specific there might however be a number of complex changes. In India as well as in China we observe a regional shift in the rainfall pattern. There are a number of processes which influence monsoon rainfall. The future evolution of the Indian monsoon is therefore difficult to project especially in light of air pollution by aerosols. Aerosols like soot absorb sun light and therefore tend to strengthen monsoon rainfall, while sulfur aerosols reflect sun light and weaken the circulation.

What would be the consequences of a changing Indian monsoon and how would it impact upon the Indian subcontinent?

Indian agriculture depends heavily on the regular occurrence of the seasonal monsoon rainfall. Changes in the past century have rarely varied by more than 10% from the long-term mean. Stronger variations could result in severe droughts or flooding with devastating impact onto Indian agriculture and therewith food supply.

Do you think the Indian scientific community is prepared to model and forecast potential changes of the Indian monsoon due to climate change?

India has excellent researchers and no monsoon region in the world has similarly impressive data coverage as the Indian summer monsoon. This puts India in an excellent position for monsoon prediction. However, monsoon dynamics are very complicated. The future evolution will depend on global emissions of greenhouse gases as well as air pollution through aerosols, i.e. smoke in its varies forms. The snow cover on the Himalayas has a strong influence as well as the El Nino Southern Oscillation (ENSO). Furthermore, our study has shown that monsoon dynamics has the potential for sudden flips. All this makes the projection of monsoon rainfall for the future a very difficult task. Given its role for the livelihood of hundreds of millions of people, the Indian society and research community can never be prepared enough, I would say.

What are the deficits and missing links in climate science with regard to South Asia and its capacity to adapt?

In my opinion global research affords need to focus more on the heavily populated regions in South Asia.

Do you intend to do any further research on South Asia and the Indian monsoon?

Yes! We are currently examining comprehensive climate model simulations with respect to the potential of abrupt monsoon transitions and are planning to apply our model to climate records of the past in order to see which role the self-amplification played in past monsoon changes. Collaborations with the Indian Institute of Tropical Meteorology in Pune and the Indian Institute of Science in Bangalore have started and will hopefully intensify in the near future.

Interview conducted by Dr. Michael Köberlein

For more information Prof. Anders Levermann, Please click here Potsdam Institute for Climate Impact Research