What is an atmospheric brown cloud?

An atmospheric brown cloud is a layer of air pollution containing aerosols like soot or dust that absorb and scatter solar radiation. These clouds, which extend up to 3 km (1.8 miles) above the Earth's surface, have regional and global climatic effects and pose risks to human health and food security. Formed by burning fossil fuels and biomass, the brown color comes from black carbon, fly ash, soil dust particles, and nitrogen dioxide. The increase in these air pollution sources results from rapid economic development. These clouds are prevalent in tropical regions due to high pollutant emissions and long dry seasons.

What causes atmospheric brown clouds to form?

Atmospheric brown clouds are caused by emissions from burning fossil fuels and biomass . The brown color comes from the absorption and scattering of solar radiation by black carbon , fly ash, soil dust particles, and nitrogen dioxide. These pollutants have increased due to rapid economic development. For example, black carbon emissions in the second half of the 20th century increased fivefold in China and threefold in India, while sulfur dioxide emissions increased tenfold in China and six- to sevenfold in India. Atmospheric brown clouds are a global issue associated with human-generated air pollution from Africa, North and South America, Asia, and Europe, and are especially common in tropical regions due to high pollutant emissions and long dry seasons.

What do atmospheric brown clouds look like and where can they be seen?

Atmospheric brown clouds are layers of air pollution containing aerosols like soot or dust that absorb and scatter incoming solar radiation. The brown color comes from the absorption and scattering of solar radiation by black carbon, fly ash, soil dust particles, and nitrogen dioxide. These clouds are a global phenomenon associated with human-generated air pollution. They are particularly prevalent in tropical regions due to high pollutant emissions and long dry seasons. The first observations were made in the late 1990s during the Indian Ocean Experiment, which revealed a large aerosol formation over South Asia and the northern Indian Ocean. This "Asian brown cloud" occurs annually from November through May. Subsequent data has shown that atmospheric brown clouds are also associated with human-generated air pollution from Africa, North America, South America, and Europe.

How do atmospheric brown clouds affect air quality and health?

Atmospheric brown clouds (ABCs) are layers of air pollution containing aerosols like soot and dust that absorb and scatter solar radiation, posing risks to human health and food security. ABCs contain particulate matter that leads to cardiovascular and respiratory problems. They also contain ozone, which can irritate lung tissue, reduce lung function, and exacerbate asthma. Changes in precipitation can modify regional agricultural production. For example, air pollution related to the Asian brown cloud reduced India's rice output by 6.2 million metric tons from 1985 to 1998.

How do these clouds influence local and global climate?

Atmospheric brown clouds contain air pollutants like dust and soot that absorb and scatter incoming solar radiation, leading to regional and global climate effects, posing risks to human health and food security. These clouds are most prevalent in tropical regions because of high pollutant emissions and extended dry seasons. Formation and Composition These clouds result from burning fossil fuels and biomass. The color comes from the absorption and scattering of solar radiation by black carbon, fly ash, soil dust, and nitrogen dioxide. Rapid economic growth has increased these pollution sources. The clouds are composed of black and organic carbon aerosols. Black carbon warms the atmosphere by absorbing solar radiation, while sulfates and nitrates reflect solar radiation back into space. Both types reduce the amount of solar radiation reaching the Earth's surface, causing a phenomenon known as dimming. Regional and Global Climate Impact Atmospheric brown clouds can affect regional climates by reducing the amount of solar radiation reaching the surface, leading to lower surface temperatures. These lower temperatures slow evaporation, reducing atmospheric water and precipitation. These clouds have contributed to decreased summer monsoon rainfall in India since 1930 and shifted the summer monsoon in eastern China southward, also changing precipitation patterns in other tropical regions. Changes in precipitation and climate due to atmospheric brown clouds can also modify regional agricultural production, with air pollution related to the Asian brown cloud associated with a reduction in Indian rice output from 1985 to 1998.

What can be done to reduce or prevent atmospheric brown clouds?

To reduce or prevent atmospheric brown clouds, techniques to control air pollution can be employed to reduce or eliminate the emission of harmful substances into the atmosphere. Changing to cleaner fuels and processes is the best way to protect air quality by reducing the emission of pollutants. Pollutants that are not eliminated can be collected or trapped by air-cleaning devices before they escape into the atmosphere. Flue gas treatment can also reduce particulate matter, nitrogen oxides, and sulfur dioxide. The economic principles behind trading in emissions can also provide solutions. For example, the U.S. Acid Rain Program successfully reduced sulfur dioxide emissions through emissions trading.

Atmospheric brown cloud

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Atmospheric brown cloud

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Last updated

Nov. 10, 2026 •History

Top Questions

What is an atmospheric brown cloud?
An atmospheric brown cloud is a layer of air pollution containing aerosols like soot or dust that absorb and scatter solar radiation. These clouds, which extend up to 3 km (1.8 miles) above the Earth's surface, have regional and global climatic effects and pose risks to human health and food security.

Formed by burning fossil fuels and biomass, the brown color comes from black carbon, fly ash, soil dust particles, and nitrogen dioxide. The increase in these air pollution sources results from rapid economic development. These clouds are prevalent in tropical regions due to high pollutant emissions and long dry seasons.
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1. atmospheric brown cloud
2. geoengineering: Cloud whitening
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What causes atmospheric brown clouds to form?
Atmospheric brown clouds are caused by emissions from burning fossil fuels and biomass. The brown color comes from the absorption and scattering of solar radiation by black carbon, fly ash, soil dust particles, and nitrogen dioxide. These pollutants have increased due to rapid economic development. For example, black carbon emissions in the second half of the 20th century increased fivefold in China and threefold in India, while sulfur dioxide emissions increased tenfold in China and six- to sevenfold in India.

Atmospheric brown clouds are a global issue associated with human-generated air pollution from Africa, North and South America, Asia, and Europe, and are especially common in tropical regions due to high pollutant emissions and long dry seasons.
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What do atmospheric brown clouds look like and where can they be seen?
Atmospheric brown clouds are layers of air pollution containing aerosols like soot or dust that absorb and scatter incoming solar radiation. The brown color comes from the absorption and scattering of solar radiation by black carbon, fly ash, soil dust particles, and nitrogen dioxide.

These clouds are a global phenomenon associated with human-generated air pollution. They are particularly prevalent in tropical regions due to high pollutant emissions and long dry seasons. The first observations were made in the late 1990s during the Indian Ocean Experiment, which revealed a large aerosol formation over South Asia and the northern Indian Ocean. This "Asian brown cloud" occurs annually from November through May. Subsequent data has shown that atmospheric brown clouds are also associated with human-generated air pollution from Africa, North America, South America, and Europe.
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1. atmospheric brown cloud
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do atmospheric brown clouds affect air quality and health?
Atmospheric brown clouds (ABCs) are layers of air pollution containing aerosols like soot and dust that absorb and scatter solar radiation, posing risks to human health and food security.

ABCs contain particulate matter that leads to cardiovascular and respiratory problems. They also contain ozone, which can irritate lung tissue, reduce lung function, and exacerbate asthma. Changes in precipitation can modify regional agricultural production. For example, air pollution related to the Asian brown cloud reduced India's rice output by 6.2 million metric tons from 1985 to 1998.
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1. atmospheric brown cloud
2. Asian brown cloud
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do these clouds influence local and global climate?
Atmospheric brown clouds contain air pollutants like dust and soot that absorb and scatter incoming solar radiation, leading to regional and global climate effects, posing risks to human health and food security. These clouds are most prevalent in tropical regions because of high pollutant emissions and extended dry seasons.

Formation and Composition

These clouds result from burning fossil fuels and biomass. The color comes from the absorption and scattering of solar radiation by black carbon, fly ash, soil dust, and nitrogen dioxide. Rapid economic growth has increased these pollution sources. The clouds are composed of black and organic carbon aerosols. Black carbon warms the atmosphere by absorbing solar radiation, while sulfates and nitrates reflect solar radiation back into space. Both types reduce the amount of solar radiation reaching the Earth's surface, causing a phenomenon known as dimming.

Regional and Global Climate Impact

Atmospheric brown clouds can affect regional climates by reducing the amount of solar radiation reaching the surface, leading to lower surface temperatures. These lower temperatures slow evaporation, reducing atmospheric water and precipitation. These clouds have contributed to decreased summer monsoon rainfall in India since 1930 and shifted the summer monsoon in eastern China southward, also changing precipitation patterns in other tropical regions. Changes in precipitation and climate due to atmospheric brown clouds can also modify regional agricultural production, with air pollution related to the Asian brown cloud associated with a reduction in Indian rice output from 1985 to 1998.
2 Britannica Sources
1. atmospheric brown cloud
2. Asian brown cloud
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What can be done to reduce or prevent atmospheric brown clouds?
To reduce or prevent atmospheric brown clouds, techniques to control air pollution can be employed to reduce or eliminate the emission of harmful substances into the atmosphere. Changing to cleaner fuels and processes is the best way to protect air quality by reducing the emission of pollutants. Pollutants that are not eliminated can be collected or trapped by air-cleaning devices before they escape into the atmosphere. Flue gas treatment can also reduce particulate matter, nitrogen oxides, and sulfur dioxide.

The economic principles behind trading in emissions can also provide solutions. For example, the U.S. Acid Rain Program successfully reduced sulfur dioxide emissions through emissions trading.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Atmospheric brown cloud, a layer of air pollution containing aerosols such as soot or dust that absorb as well as scatter incoming solar radiation, leading to regional and global climatic effects and posing risks to human health and food security. This layer extends from Earth’s surface to an altitude of roughly 3 km (1.8 miles).

The presence of so-called brown clouds of pollution over urban areas has been of concern for decades. Urban brown clouds are heavily influenced by thermal inversions in the atmosphere and occur over several cities. Atmospheric brown clouds, in contrast, are a more widespread, regional phenomena. The first observations of these phenomena were made in the late 1990s as part of the Indian Ocean Experiment (INDOEX), in which coordinated air pollution measurements were taken from satellites, aircraft, ships, surface stations, and balloons. The INDOEX observations surprised researchers by revealing a large aerosol formation over most of South Asia and the northern Indian Ocean. This “Asian brown cloud” is an annual phenomenon that occurs primarily from November through May. Subsequent data have shown that atmospheric brown clouds are a global phenomenon and are associated with human-generated air pollution from Africa, North America, South America, and Europe, as well as Asia. Atmospheric brown clouds are particularly prevalent in tropical regions; they occur as a result of elevated pollutant emissions and a lengthy dry season that prevents aerosols from being removed from the atmosphere through precipitation.

Atmospheric brown clouds are caused by emissions associated with the combustion of fossil fuels and biomass. The brown colour of the clouds results from the absorption and scattering of solar radiation by black carbon, fly ash, soil dust particles, and nitrogen dioxide. Such sources of air pollution have increased in the past several decades because of rapid economic development. For example, in the second half of the 20th century, black carbon emissions increased by a factor of five in China, and soot emissions rose by a factor of three in India. Sulfur dioxide emissions increased 10-fold in China and 6- to 7-fold in India over the same period.

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Clouds and Cloud Types

Aerosols in brown clouds are made up primarily of black carbon and organic carbon. These aerosols, especially the black carbon component, absorb solar radiation, and this absorption results in enhanced solar heating of the atmosphere. Other aerosols, such as sulfates and nitrates, scatter solar radiation back to space. The presence of both types of aerosols in the air reduces the amount of solar radiation reaching the surface of the Earth, producing a phenomenon called “dimming.” This type of radiative forcing is referred to as the “aerosol direct effect.” In addition, aerosols can influence the formation of clouds, known as the “aerosol indirect effect.” Atmospheric brown clouds contain a mixture of both types of aerosols. Because of the effects of atmospheric brown clouds, India and China are dimmer at the surface today by at least 6 percent compared with their state in preindustrial times.

Changes in the amount of solar radiation reaching Earth’s surface because of atmospheric brown clouds can influence the regional climate. A reduction in the amount of solar radiation reaching the surface leads to lower surface temperatures. Lower temperatures slow the rate of evaporation, which reduces the amount of precipitable water in the atmosphere. The resulting declines in precipitation can influence the regional hydrological cycle. For example, atmospheric brown clouds have played a major role in decreases in summer monsoon rainfall in India since 1930. In addition, aerosol pollution has been linked to the southward shift of the summer monsoon in eastern China and to changes in precipitation patterns in other tropical regions.

Changes in precipitation and climate due to atmospheric brown clouds can modify regional agricultural production. These impacts are complex and are likely to be different depending on crop types. One study estimated that from 1985 to 1998 Indian rice output was reduced by 6.2 million metric tons (about 6.8 million tons—that is, enough rice to feed 72 million people) because of air pollution related to the Asian brown cloud.

In addition, pollution from atmospheric brown clouds is a threat to human health. Particulate matter, such as soot and dust, has been linked in epidemiological studies to cardiovascular problems, chronic respiratory problems, and mortality. Brown clouds also contain ozone and other hazardous pollutants. Ozone can irritate lung tissue, exacerbate asthma, and reduce lung function. Ozone has also been linked to reduced crop yields.

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