Tropical forests draw down and store large quantities of CO₂ from the atmosphere. The Amazon rainforest in South America, for example, stores approximately 123 billion tons of carbon—more than is stored in any other terrestrial ecosystem in the world. But these forests are facing a critical challenge.
Research from 2023, which was carried out by me and more than 100 colleagues, found that tropical forests in South America are vulnerable to climate extremes. We determined that during an El Niño event, the warm phase of a natural fluctuation in Earth's climate system, South American tropical forests may fail to act as a carbon sink.
This finding becomes even more alarming when we consider the increasing frequency and intensity of El Niño events. There have been twice as many "very strong" El Niños in the past 60 years as there were in the 60 years before that. And the U.S. National Oceanic and Atmospheric Administration has recently confirmed that such an El Niño is currently underway.
Tropical forests absorb CO₂ through the process of photosynthesis and convert it into biomass. However, the balance between photosynthesis and respiration is delicate and depends on two factors: temperature and water availability.
In hotter and drier conditions, plants close the pores of their leaves to avoid water loss. But closing them effectively cuts off a plant's fuel supply because it is through these pores that they absorb CO₂. This starves plants of the carbon needed for photosynthesis and growth.
During El Niño years, which are characterized by high-temperature anomalies, prolonged climate stress leads to reduced forest growth and increased tree mortality. The effects of this are felt for decades as carbon is released back into the atmosphere when the dead trees decompose.
Source: Phys.org
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