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The Tipping Point

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In the 1970s, scientists made an incredible discovery: the Amazon generates about half of its own rainfall through evaporation and transpiration. The Amazon’s nearly 390 billion trees act as giant pumps, sucking water up through their roots and releasing it through their leaves. On a typical day, the Amazon releases 20 billion tons of moisture into the atmosphere. As these clouds move westward across the Amazon, moisture is recycled from sky to land five to six times.1 This hydrological cycle provides critical moisture for agriculture in southern parts of South America and affects rainfall patterns as far as the Midwest in the United States.2, 3

But this discovery raised a new concern: if trees play such an important climactic role, what happens when we lose those trees? Though scientists are still puzzling over this, current findings appear bleak. Deforestation, fires, climate change and other man-made factors decrease rainfall and cause the forest to dry out, leading to even more droughts, wildfires, and lengthier dry seasons. Eventually, there may not be enough trees to keep the cycle going, triggering a total ecosystem shift from rainforest to savannah. This threshold is called the tipping point.

Initial estimates found that the Amazon would reach a tipping point at around 40% forest loss, but in 2018 renowned Amazon experts Carlos Nobre and Thomas Lovejoy projected that, due to the synergistic effects of fires and climate change, the tipping point could occur at 20-25% loss. Currently, nearly 20% of trees have been lost in the Brazilian Amazon and about 17% across the entire Amazon basin.4 Some scientists claim that early signs of the tipping point are already visible, citing prolonged dry seasons, increased droughts, and a rise of dry-adapted trees, particularly in the south and southeast of the Amazon basin.5

While there is some debate as to exactly when and how the Amazon will reach a tipping point,6 nearly everyone agrees on one point: we don’t want to wait to find out. Losing the Amazon rainforest would have global consequences, disrupting weather patterns across much of South America and releasing massive amounts of CO2 into the atmosphere. The time for a sustainable Amazon is now.

Works Cited

  1. Lovejoy, T. E., & Nobre, C. (2018). Amazon Tipping Point. Science Advances, 4(2), eaat2340. https://doi.org/10.1126/sciadv.aat2340.
  2. Fassoni-Andrade, A., Fleischmann, A., Papa, F., Cauduro Dias de Paiva, R., Wongchuig, S., Melack, J., Moreira, A., Paris, A., Ruhoff, A., Barbosa, C., Maciel, D., Novo, E., Durand, F., Frappart, F., Aires, F., Abrahão, G., Ferreira-Ferreira, J., Espinoza, J., Laipelt, L., & Pellet, V. (2021). Amazon Hydrology From Space: Scientific Advances and Future Challenges. Reviews of Geophysics, 59, 97. https://doi.org/10.1029/2020RG000728
  3. Lawrence, D., & Vandecar, K. (2015). Effects of tropical deforestation on climate and agriculture. Nature Climate Change, 5(1), 27–36. https://doi.org/10.1038/nclimate2430
  4. Lovejoy, T. E., & Nobre, C. (2019). Amazon tipping point: Last chance for action. Science Advances, 5(12), eaba2949. https://doi.org/10.1126/sciadv.aba2949
  5. Esquivel-Muelbert, A., Baker, T. R., Dexter, K. G., Lewis, S. L., Brienen, R., Feldpausch, T. R., Lloyd, J., Monteagudo-Mendoza, A., Arroyo, L., Álvarez-Dávila, E., Higuchi, N., Marimon, B. S., Marimon-Junior, B. H., Silveira, M., Vilanova, E., Gloor, E., Malhi, Y., Chave, J., Barlow, J., Bonal, D., … Phillips, O. L. (2019). Compositional response of Amazon forests to climate change. Global change biology, 25(1), 39–56. https://doi.org/10.1111/gcb.14413
  6. Amigo, Ignacio (February 12, 2020). “When will the Amazon Hit a Tipping Point?” Nature. https://www.nature.com/articles/d41586-020-00508-4