Amazon River basin may not be resilient to climate change, Berkeley Lab researchers suggest

Qing Zhu/Courtesy

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The Amazon River basin in Brazil, a large carbon sink, is transitioning into a carbon source — and California could be largely affected.

According to a recent paper submitted by an international team of scientists including some from Lawrence Berkeley National Laboratory, current estimates regarding the rainforest’s carbon uptake are not entirely comprehensive. In fact, the resilience of the region to climate change could be much less than previously predicted, which could cause global temperatures to rise.

“The ability of Amazon forests to secure atmospheric CO2 in the future is much lower than what we have estimated in the future projections given the strong phosphorus limitation. It means we are too optimistic now,” Qing Zhu, a paper co-author and research scientist at Berkeley Lab, said in an email. “The actual future warming could be much larger than what we expect.”

Phosphorus is a critical element for photosynthesis because it is a compound in adenosine triphosphate, or ATP. ATP provides the energy that allows photosynthesis to occur.

While some models predict that the forest will still act as a carbon sink due to rising carbon dioxide levels, soil phosphorus impoverishment will reduce carbon dioxide-induced biomass carbon growth, according to the study. When phosphorus-deficient soils in the Amazon are taken into account, carbon dioxide reuptake is reduced by 50 percent.

“With more CO2, there is an increase in productivity,” said Jeff Chambers, a campus professor of geography. “But there are many caveats. One of the caveats is if you give plants more CO2 but they’re on nutrient-deficient soils, then the response of the plants to CO2 might be much less.” 

While the rainforest’s soils are phosphorus deficient, there are other sources of the mineral outside the Amazon region. 

For instance, phosphorus can be carried through dust from the Sahel region in Africa, where it is then deposited over the Amazon, according to Zhu. The mineral can also be carried to the rainforest through ashes from wildfires.

The forest could hypothetically be fertilized like an agricultural system, according to Zhu. However, this would come with complicated consequences that could change the regional water quality and the rainforest’s food web.

“Consequences are complicated and beyond the scope of just CO2 uptake. … It still requires more studies to assess the full spectrum of the impacts both positive and negative, before we can artificially fertilize amazon forest with phosphorus,” Zhu said in an email.

The paper’s findings indicate a more sinister trend in the rapidity of the greenhouse effect due to increased anthropogenic emissions, such as carbon dioxide.

If the Amazon rainforest sequestrates less carbon dioxide from the atmosphere, the whole globe will experience a higher carbon dioxide level and a warmer climate, according to Zhu in the email. Warming would likely increase California’s water loss from land into the atmosphere in a process called evapotranspiration, creating a drier and hotter environment in an already dry state.

A hotter and drier climate, would, in effect, increase tree mortality and provide more dry fuel for wildfires, according to Zhu. 

Alex Casey is the city news editor. Email her at [email protected] and follow her on Twitter at @acasey_dc.