Engineering: Himalayan glaciers threatened by air pollution

 

Scientists have blamed 'brown clouds' of pollutants over South Asia for contributing to the melting of Himalayan and other tropical glaciers.

However, researchers at Scripps Institution of Oceanography at the University of California hope that cutting down on air pollution could halt the retreat of such glaciers.

The research team, led by Professor V. Ramanathan, found that atmospheric brown clouds amplified the Sun’s heating of the lower atmosphere by about 50 per cent.

These clouds, containing soot, trace metals and other particles from a range of urban, industrial and agricultural sources, added to the heating effect resulting from greenhouse gases.

The research, published yesterday in the journal Nature, concluded that together, these two phenomena accounted for the retreat of Himalayan glaciers observed over the past 50 years.

These glaciers are of great importance to the region, supplying water to major Asian rivers including the Yangtze, Ganges and Indus. A reduction in water flow could compromise the principal water supply for billions of people in China, India and other south Asian countries.

"The rapid melting of these glaciers, the third-largest ice mass on the planet, if it becomes widespread and continues for several more decades, will have unprecedented downstream effects on southern and eastern Asia," stated the paper’s authors.

"The main cause of climate change is the build up of greenhouse gases from the burning of fossil fuels," said Achim Steiner, United Nations under-secretary general and executive director of the UN Environment Programme (UNEP), which helped support the research.

"But brown clouds, whose environmental and economic impacts are beginning to be unravelled by scientists, are complicating and in some cases aggravating their effects."

Steiner urged the international community to take action, adding: "It is likely that in curbing greenhouse gases we can tackle the twin challenges of climate change and brown clouds and in doing so, reap wider benefits from reduced air pollution to improved agricultural yields."

Unmanned aircraft collected research data

The research was based largely on data collected by a fleet of unmanned aircraft during a landmark field campaign conducted in March 2006 over the Maldives, in the Indian Ocean.

Flying in stacked formation, the aircraft simultaneously sampled air at different altitudes, creating a detailed vertical profile of particle concentrations and light absorption.

The Maldives Autonomous unmanned aerial vehicle Campaign (MAC) took place during the region's dry season, when clouds of polluted air travel south from the continent to the Ocean.

The air typically contains particles released from industrial and vehicle emissions as well as through biomass burning.

The pollution warms the atmosphere due to particles absorbing sunlight, whilst also cooling the Earth's surface as the particles filter out light which would otherwise reach the ground.

The overall effect of the two forces remains uncertain, but other research by Ramanathan has suggested that the cooling of the ground, known as global dimming, might mask the effects of global warming, leading scientists and the public to underestimate the full magnitude of climate change.

Using computer climate models, the researchers estimated that the region's atmosphere has warmed by 0.25°C per decade since 1950 at altitudes ranging from two to five kilometres above sea level.

Many of the glaciers in the Himalayas are found in this range. The amount of heating equally corresponds to observed levels of glacial retreat.

Analysis revealed that the effect of the brown cloud was necessary to explain temperature changes that have been observed in the region over the last half-century. It also revealed that south Asia's warming trend is more pronounced at higher altitudes than closer to sea level.

"The conventional thinking is that brown clouds have masked as much as 50 per cent of the global warming by greenhouse gases through the so-called global dimming," said Professor Ramanathan.

"While this is true globally, this study reveals that over southern and eastern Asia, the soot particles in the brown clouds are intensifying the atmospheric warming trend caused by greenhouse gases by as much as 50 per cent."
 

You’ve read it. Now review it.

Back to top

Back to top