Behind the Forecast: Amazon’s impact on worldwide weather

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Behind the Forecast: Amazon’s impact on worldwide weather
The map shows active fire detections in Brazil as observed by Terra and Aqua MODIS between August 15-22, 2019. (Source: NASA Earth Observatory)

LOUISVILLE, Ky. (WAVE) - The Amazon rainforest has been ruling news headlines and social media feeds for the past few weeks as fires rage across it. However, not all the information being spread like wildfire on the internet is true.

Many refer to the Amazon as the "lungs of our planet" and say that it produces 20% of the planet's oxygen. That's not quite true.

Yes, nearly all of the free oxygen in our atmosphere is produced through photosynthesis by plants. One-third of the photosynthesis does occur in tropical forests; the Amazon Basin contains the largest of these forests. However, almost all of the oxygen created by plants is consumed by living organisms and fires. This means, at the end of the day, there’s a nearly net-zero production of oxygen.

"There is a net release of oxygen while the tree is growing and storing carbon in its wood, but when the tree dies the wood rots, removing the same amount of oxygen from the air to form carbon dioxide (CO2) from the carbon in the wood," Philip Fearnside, Brazil National Institute of Amazonian Research professor, said in an interview with Newsweek.

Oxygen can only accumulate in our atmosphere when it's unable to recombine with carbon to create CO2.

Overall the world's oxygen supply is quite stable. Our atmosphere is made up of 20.95% oxygen and researchers say our supply is unlikely to change much even if the Amazon completely disappeared; only a one percent drop is estimated.

While oxygen supply isn't expected to be impacted by the extinction of the Amazon rainforest, worldwide rainfall could see a dramatic shift.

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A 2014 study found that a "complete Amazon deforestation would reduce rainfall in the U.S. Midwest, Northwest and parts of the American south during the agricultural season."

While parts of the United States could see drier conditions, the extinction of the Amazon could also cause higher rainfall in parts of the United Kingdom and Hawaii.

The reason for this change: transpiration.

Transpiration is the evaporation of water from plants through small openings on the underside of leaves called stomata. In most plants, transpiration is mostly controlled by the atmospheric humidity and soil moisture content.

Trees pull gallons of water from the ground and push it into the air through transpiration. On average one large tree can pull 100 gallons of water out of the soil, according to American Forests. One calculation found that the Amazon rainforest can pump 20 billion tons of water into the atmosphere each day.

When water vapor then condenses into clouds, it lowers air pressure and the surrounding air temperature. When there is a decrease in atmospheric pressure, more air is pulled into the area from elsewhere potentially drawing in more moisture. By this process, the Amazon rainforest creates cloud cover and in turn its own rain.

The moisture does not all stay over the Amazon to become clouds. Some of it travels west with the trade winds where it is blocked by the Andes mountain range where it can condense into clouds and produce immense amounts of rainfall. A portion of that moisture flows south, helping to produce rain across South America. Our atmosphere is all interconnected so the moisture ripples around our planet and can potentially contribute to the rain here in the United States.

One study found that if the Amazon was completely gone, the snowpack in the Sierra Nevada mountains would be reduced by half. This would be detrimental to California who relies on this snowpack as a crucial water reservoir.

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