"Brown clouds are a transcontinental issue"

Asian Brown Clouds created a lot of heat in South Asia, a few years ago (see: 'Aerial Raid,' Down To Earth, August 15, 2002). Now the chief proponent of the phenomenon, Veerabhadran Ramanathan, director of the Center for Atmospheric Sciences at the Scripps Institution of Oceanography, University of California, USA, says these clouds are a problem for other regions of the world as well. He spoke to Dinesh C Sharma

Last Updated: Saturday 04 July 2015

Why has the Asian Brown Cloud now become the Atmospheric Brown Cloud?
Brown clouds have been seen all over the world, including the us , Europe, India and China. Earlier, our focus was on South Asia; so we called these clouds the Asian Brown Cloud. Several Indian scientists and politicians criticised this appellation as politically-motivated. We agreed that the nomenclature was inaccurate, though we did not think that this had anything to do with politics. Anyhow, we changed the brown cloud's name to Atmospheric Brown Cloud. This name is scientifically apposite. But we have persisted with the acronym, abc, simply because it's very popular.

Since your 1999 findings on the effects of brown clouds in the Indian Ocean, have there been similar studies in other parts of the world?
Immediately after our Indian Ocean experiments (indoex), there were two similar studies -- one by Swiss researchers and the other by a us- Israel group. These showed that the brown cloud problem was not just confined to the Indian Ocean area. The indoex study also influenced the later researchers to ascribe brown clouds to pollution. And then in 2000, the National Aeronautical and Space Administration, usa, launched a new satellite, Terra. This satellite had an instrument called Modus, which could look at aerosols over continents. Earlier, we knew about aerosols only over the oceans. But Modus clearly showed that what we thought was the Asian Brown Cloud was actually part of a much larger cloud: it affected continents. So, we proposed that brown clouds are a transcontinental issue and asked the un to initiate a new programme. Now, we have a larger abc programme, with special focus on Asia. We have been able to rope in scientists from China, Thailand, India and Korea.The programme is backed by the United Nations Environment Programme and is funded by many governments, including that of China and the us.

Is India also funding the programme?
Indian scientists do participate in the investigating teams and the Indian government has talked of giving official sanction to their efforts. But that hasn't happened yet.

Is this new experiment on the lines of the INDOEX?
indoex was a three-month experiment, confined to the dry season in India. The new experiments cover Asia, the Indian and the Pacific oceans. The key issue is that if pollution stays within land, its impact on monsoon and climate would have been relatively smaller than that caused by brown clouds. Effects of abc on monsoon are large, primarily because of the spread of the pollution over the Arabian Sea and the Bay of Bengal. Such pollution affects sea surface temperatures, which in turn affect monsoon circulation and climate. We need to look at long-term developments to analyse such processes. So, we are setting up observation stations to look at both dry and the wet seasons, and over longer periods.

We hope to identify the chemical constituents of brown clouds. We can then advise governments on regulating them. Right now, we suspect that black carbon -- emitted by diesel combustion, and wood fires -- is the most damaging constituent of brown clouds. But it's going to take us a few more years to collect data to give concrete suggestions to governments.

Tell us about the relation between brown clouds and global warming
Our model calculations seem to suggest that greenhouse gases are the major cause of warming of the Indian Ocean. Brown clouds, in contrast, decrease sunlight: so they mask global warming. So, if we curb the prime cause of abc, air pollution -- which we will have to, sooner than later -- the Indian Ocean will be much hotter.And that will have both positive and negative impacts. Large warming produces more water vapour, so there would be more rainfall. But this could cause floods in regions that already have heavy rainfall. Also, brown clouds cool down the Northern Indian Ocean, while the monsoon system prefers a warm ocean. So, we fear that the monsoon is migrating south of India and it's raining more over the Indian ocean at the expense of the country's landmass. I wish there was more research by Indian meteorologists on this issue.

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