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One of my students recently heard on NPR about how transpiration of trees in the Amazon Rain Forest directly affects the weather and climate in region. She is wondering how this occurs. Could you shed some light on this and how the climate will change as a result of deforestation in that area? Thank you!
Question Date: 2015-11-30
Answer 1:

The Amazon rainforest is so densely forested that it is responsible for providing 20% of the Earth's oxygen. So indeed, the local atmosphere is oxygen-rich there compared to further away parts of the world. The deforestation of this part of the world has several exacerbating effects on global climate change.

When trees are burned, much of the carbon that they stored in their wood and leaves will be released into the atmosphere, primarily in the form of the greenhouse gas, CO2. The burning also produces ash and char, which is black. The ash from rainforest destruction travels with the winds, circling the globe and depositing everywhere. This reduces the overall reflectance (albedo) of the earth, especially in snowy areas like the poles. Reduced albedo enhances warming effects because more sunlight is absorbed and less reflected. It's a feedback loop because warming also melts snow, which further reduces albedo.

Finally, because the forests are no longer growing after destruction, their future potential to fix carbon from the atmosphere is obliterated.

Answer 2:

Scientists found that the air masses that traveled over the rainforest absorbed a lot of moisture. The more vegetation they travel over, the more moisture they absorb, which is then carried away from the rainforest and precipitates elsewhere. As deforestation occurs, the surrounding areas will receive less rain and become drier climates.

Answer 3:

Plants transpire (evaporate) water as part of the way they draw nutrients out of the soil. This evaporation increases the humidity as the trees store water and then release it. That water rises up as vapor, forms clouds, and then rains back down to Earth, completing the cycle as it is taken up by another plant. In the Amazon, this has the effect of greatly increasing the amount of rainfall that the region experiences, because the trees are constantly recycling water into the atmosphere and then down to the ground again. Were the forest not there, the water would just flow into the river and then out to sea, and the total amount of rainfall would decrease dramatically.

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