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Climate Change Could Bring Drought to Amazon, Greater Rain to Pacific and African Forests

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Rising carbon dioxide levels could lead to fewer moisture clouds forming over the Amazon rainforest. Ana_Cotta / CC BY 2.0

Scientists have discovered another factor that might interact with rising carbon dioxide emissions to influence climate change—tropical forests.

In a study published in Nature Climate Change Friday, researchers found that the way tropical forests interact with increased atmospheric levels of carbon dioxide could alter rainfall patterns, drying out the Amazon rainforest and increasing precipitation in African and Indonesian forests.


"People tend to think that most of the disruption will come from heat going into the oceans, which, in turn, will alter wind patterns," University of California, Irvine (UCI) professor and study author James Randerson said in a UCI press release. "We have found that large-scale changes in rainfall can, in part, be attributed to the way tropical forests respond to the overabundance of carbon dioxide humans are emitting into the atmosphere, particularly over dense forests in the Amazon and across Asia."

These big effects start with tiny holes. Trees have openings in the underside of their leaves called stomata, which open and close to regulate the amount of carbon dioxide a tree takes in and the amount of water vapor it releases. When there is more carbon dioxide in the atmosphere, the stomata do not need to open as widely, and therefore release less water vapor.

"In many tropical forest regions, the moisture supplied by transpiration, which connects water underground at the root level directly to the atmosphere as it is pulled up to the leaves, can contribute as much as moisture evaporated from the ocean that rains back down at a given location—which is normal rainforest recycling," study lead author Gabriel Kooperman said in the press release.

The researchers used climate models to study how rising carbon dioxide levels would interact with forests to change the climate on various continents.

They found the Amazon rainforest was most at risk of drought and forest mortality due to rising carbon dioxide. Kopperman explained that, as stomata in the Amazon release less water vapor, fewer clouds will form over the forest. This will mean that water vapor from the Atlantic Ocean will not have pre-existing clouds to bond with, and will instead blow over the forest to the Andes.

However, this effect was not predicted to occur in other tropical forests. Forests in Africa and on islands in Malaysia, Papua New Guinea and Indonesia were predicted to see increased rainfall.

On island forests in particular, this is because the reduced moisture will increase temperatures over the islands relative to the surrounding ocean air, pulling in greater moisture from ocean systems.

Kooperman said both drought and floods caused by increased rainfall could have serious consequences both for biodiversity and for food and water access for impoverished populations.

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