The impact of brown clouds on our climate: Professor Ramanathan calls for a fast response in an ICIMOD Knowledge Forum

Professor Veerabhadran Ramanathan, Distinguished Professor of Climate and Atmospheric Sciences, Scripps Institution of Oceanography, University of California in San Diegiho, gave a presentation on ‘The Extreme Vulnerability of the Himalayan-Tibetan Region to Global Warming and Air Pollution’ at an ICIMOD Knowledge Forum on 22 March 2011.

Prof. Ramanathan has received numerous international scientific awards for his pioneering studies in climate and environment, including his contribution to the discovery of atmospheric brown clouds (ABCs) over Asia containing black carbon mainly from bio-fuel burning. ABCs have led to large scale dimming and decreased monsoon rainfall and rice harvest in India, and contributed to the melting of Himalayan glaciers. All this has profound implications for the lives and livelihoods of people living within and downstream of the mountains, which are the sources of ten of Asia’s major rivers. 

In his talk, Prof. Ramanathan described how black carbon aerosols have contributed to the formation of ABCs that extend across the region as a visible blanket. Sources include burning of biomass for cooking and heating; vehicle exhaust, especially diesel; factory chimneys; and forest fires. Global warming is attributed to a great extent to the increase in concentration of greenhouse gases in the atmosphere. But the role black carbon aerosols play is now increasingly recognised. All measures of mean global temperature – be it land surface temperature, ocean surface temperature, marine air temperature, or tropospheric temperature – tell the same story: that average global temperature has been rising since the Industrial Revolution. Observations have also found that the annual mean surface air temperature increase has been greater on average at higher elevations than at lower. This has profound implications for the Himalayan-Tibetan region. 

The impacts of ABCs are beginning to be felt in the region. ABCs are contributing to overall warming of the atmosphere, melting of the glaciers, reduced sunlight, and increased heavy rainfall with less rain overall. At the same time, as the atmospheric temperatures rise, more precipitation in the mountains falls as rain and less as snow. Both these effects lead to an increase in immediate runoff and decrease in water storage in the mountain areas. Black carbon deposited on snow leads to less reflection and increased absorption, which increases the rate of melting. Spring time warming and snow melting earlier in the season are contributing to drier summers, resulting in increase in the occurrences of drought situations and forest fires. The haze also results in dimming, at least 6% over China, which can reduce crop production, and cut down on evaporation again leading to reduced precipitation.

Prof. Ramanathan proposed pathways to limit global temperature increase to 2 degree Celsius: reduce CO2 by 50% by 2050; and reduce short-lived warming agents -- black carbon, ozone, methane, etc – by roughly 30% in the next 30 years thus buying time for developing transformational technologies for energy development. Around 60% of black carbon emissions can be prevented, this requires local action. Project Surya, a pilot in India, is helping the poor climb up the energy pyramid by doing just that.

Last but not least, he noted that the Himalayan-Tibetan region is especially vulnerable to global warming and air pollution, and can’t wait for governments to agree to a binding roadmap. Whatever is done, temperature increases in the Himalayan region will be higher than the global average. He urged everyone to think globally, assess regionally and act locally, and to seek integrated solutions through innovation in science, technology, policy, politics, institutions, and finance.

In a questions and answer session Prof. Ramanathan agreed with the observation that cooling is particularly severe in Terai in winter, when many die of cold waves. People also burn more to stay warm in winter in the Terai, which sets off a vicious cycle. Regarding the increase in the frequency of wildfires in recent years, which means release of more and more black carbon into the atmosphere, he proposed fire control as an adaptation measure and suggested that the Himalayan-Tibetan region can learn from the California experience. As to whether population growth was aggravating air pollution/global warming, he answered that about 80% of the green house blanket comes from 10-15% of the population. He said it might be more useful to look at per capita consumption of bio fuel, and emphasized developing/scaling up better technologies and cleaner energy as possible solutions.. 

- Ujol Sherchan,