Asian Brown Cloud

Asian Brown Cloud Photo Credit: NASA.

In developing areas of the world, including parts of Asia, rapid industrialization has brought about more cars, more factories, and more people to burn coal and wood for cooking purposes. Those activities throw a lot of soot and other pollutants into the air. In this Science Update, you’ll hear about an effort to measure the pollution over Asia and assess its impact on humans and the environment.


A haze over Asia. I'm Bob Hirshon and this is Science Update.

We think of smog as being localized to urban areas, like Los Angeles and Mexico City. But according to V. Ramanathan, director of the Center For Clouds, Chemistry, And Climate, that's not always the case.

He says scientists at the center recently helped complete a project called the Indian Ocean Experiment, or INODEX.

We discovered a huge—what we call now an Asian brown cloud—a haze layer surrounding the whole northern Indian Ocean, and much of South Asia, India, Pakistan, Southeast Asia, and China. And in fact, this happens for about three, four months a year.

As part of INDOEX, an international team of scientists used aircraft, ships, balloons, and satellites to map out the cloud and determine its composition. Besides being nasty to breathe, Ramanathan says the thick haze scatters sunlight, cutting back on evaporation from the ocean.

So if you reduce the sunlight, we are concerned you will reduce the rain in the region. And as you know, if anything, the Asian region—they need water.

So efforts to reduce pollution would not only improve the health of humans, but also the long-term health of the world's climate.

For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

In recent years, scientists have discovered a number of large, disturbing environmental patterns that shrink and swell seasonally and appear to be caused by human activities. Perhaps the most famous is the enormous "ozone hole" over Antarctica, in which the upper atmosphere's protective ozone layer has become alarmingly thin. Another is the "dead zone" at the bottom of the Gulf of Mexico: an area of oxygen-starved water that swells to the size of New Jersey in midsummer and has been linked to massive deaths of fish and shellfish.

Now we can add the Asian Brown Cloud to that ignominious list. When the researchers first began noticing this smoggy haze, they thought it might be confined to major cities. As it turns out, it's an enormous blanket covering much of the area around the northern Indian Ocean. This part of the world is home to nearly 3 billion people, or about half the world's population, and it's industrializing rapidly. Most of the new industries there are using old-fashioned, highly polluting engines and fuels.

The cloud peaks in size during the winter, when the temperature of the air tends to be hotter than the ground. That situation is called an "inversion," and the upshot is that pollutants get trapped in the atmosphere and can't move. It's like putting a lid on a pot. Seasonal variations like this affect pollution in American cities as well; for example, Los Angeles experiences a similar inversion during the summer months, which tends to be the smoggiest time there.

The INODEX study involved over 250 scientists from the U.S., Europe, and  India, with Ramanathan and Dr. Paul Crutzen serving as co-chief scientists. When the researchers studied the haze over Asia, they found that it was made of soot, ash, dust, and airborne chemicals—all products of human-made pollution. Scientists are concerned not only because this air might be dangerous to breathe, but also because it can impact the climate of the entire region. That's because the pollution in the atmosphere tends to scatter sunlight, which means the ocean doesn't get heated up as much as it usually does. If that happens, less water could evaporate into the sky and return to the earth as rain—and as Ramanathan points out, the last thing this area needs is less rain. However, he also notes that any resulting reduction in rainfall wouldn't necessarily happen in the polluted area, but possibly in some other region far from the source of the smog.

Now try and answer these questions:

    1. What is the Asian Brown Cloud?
    2. Why does it come and go with the seasons?
    3. Why might it change the amount of rainfall in the area around the Indian Ocean?
    4. If the rainfall levels do drop because of the pollution, what are several other consequences that might follow?
    5. Can you think of other examples of man-made pollutants that could affect the normal functions of the earth?
    6. Almost every form of pollution could be reduced—but in many cases, the solutions are considered too expensive. Can you name some examples? How would you suggest balancing the needs of the economy against the needs of the environment?

For Educators

Asian Dust Clouds depicts the effects of dust clouds from Asia on various sites in the United States. This page also has links to a number of news stories about Asian dust clouds over the last few years.

Read more about INDOEX in the online article "Pollution cloud threatens Asia." According to astronauts in the International Space Station, the Earth is becoming less blue and more blurred when viewed from space.

Find out what increased levels of smog might have to do with this by reading the online article "Smog clouds view from space station."

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