Amazon smoke slows formation of clouds, rainfall

Ilan Koren: If you look on satellite images over the Amazon, over most of South America, during the dry season, you’ll see many days that you cannot see the surface due to the presence of the Amazon smoke.

Atmospheric scientist Ilan Koren is with the Weizmann Institute of Science. The Amazon smoke, he said, is mostly due to man-made forest fires. The likelihood for natural fires in the Amazon is very low. Using NASA satellite images, Koren compared clouds with and without the smoke. He found that this smoke slows the formation of clouds and rainfall.

Ilan Koren: And we see very dramatic differences.

Koren said clouds generally cool the planet by reflecting sunlight. But dark particles of smoke, called aerosols, from the Amazon fires absorb more sunlight, and heat up.

Ilan Koren: And therefore clouds will form less. The net effect of the aerosols due to suppressing clouds would be more warming. So it’s a very complicated system.

What’s more, the smoke can change where the rain falls.

Ilan Koren: The same cloud that naturally would precipitate over the forest now can form away from the forest, and therefore it can change the whole hydrological cycle of the Amazon basin.

Our thanks to NASA‘s Terra Mission, helping us better understand and protect our home planet.

Our thanks to:
Ilan Koren
Weizmann Institute of Science
Rehovot, Israel

March 29, 2009

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