- A recent study finds that tropical carbon sinks have become increasingly vulnerable to water scarcity since 1960, and are consequently less able to absorb carbon dioxide.
- These findings suggest that tropical ecosystems are less resilient to climate change than previously thought.
- While the study doesn’t necessarily make projections for the future, the findings suggest that an acceleration of climate change, which is very likely to bring more drought, could further limit the ability of tropical ecosystems to absorb carbon dioxide, which, in turn, would worsen climate change.
Research has found that drought and declining water availability are increasingly impeding the ability of tropical ecosystems to soak up carbon dioxide, making the tropics a less effective carbon sink. This finding comes at a time when governments and businesses are relying heavily on the effectiveness of tropical forests to take up CO2 and store it to mitigate the impacts of rising greenhouse gas emissions and human-induced climate change.
Over the past 60 years, it’s estimated that tropical ecosystems took in about 32% of human-produced CO2, preventing it from entering the atmosphere and contributing to warming. However, this vital carbon uptake process has declined in efficiency as climate change elevates global temperatures and gives rise to extreme weather events, particularly drought, according to research. The world is currently experiencing the start of an El Niño weather pattern, which is predicted to bring more drought to many tropical regions already suffering from the stress of climate change.
In a recent study published in Nature, scientists investigated the correlation between water availability in the tropics and the carbon cycle over time. They found that tropical carbon sinks became increasingly vulnerable to water scarcity over the period from 1960 to 2018, with the most significant impacts observed during the three decades between 1989 and 2018. These findings suggest that decreased water availability is inhibiting carbon uptake, and indicates that the tropics are less resilient to climate change than previously thought.
“We found that climate models are underestimating the observed effects of tropical water variability and droughts for the global carbon cycle,” study co-author Sonia Seneviratne, a climate scientist at the Institute for Atmospheric and Climate Science at ETH Zürich, told Mongabay in an email. “This is very worrisome, because it could mean that projections are too optimistic with respect to the potential feedback of future changes in droughts for the global carbon cycle, for instance, regarding the global warming level at which the Amazon rainforest could become a much less effective carbon sink or even a carbon source.”
The study builds upon a previous paper co-authored by Seneviratne that found that global terrestrial ecosystems were less able to absorb carbon during severe droughts. The new study in Nature, which draws on historical records of global atmospheric CO2, along with terrestrial water storage and precipitation, is showing that this effect has become pronounced over time.
However, the authors note that significant uncertainties exist in the feedback loops between terrestrial carbon sinks and climate change, making it “difficult to predict how the land carbon sink will respond to future climate change.”
Maria del Rosario Uribe, an ecologist and postdoctoral scholar at Yale University in the U.S. who was not involved in this specific study, said the researchers’ conclusions weren’t surprising since water is known to be “the main limiting factor for photosynthetic activity and plant growth in the tropics.” But she added that the study can “help us understand exactly how climate is interacting with carbon.”
“Even though water availability predictions are difficult to make, the likelihood of longer and more intense droughts in the tropics in the future is very high,” Uribe told Mongabay in an email. “This means we’re facing an [imminent] threat to photosynthetic activity, tree mortality, and ecosystem stability. We are seeing it in the field and in remote sensing studies, and we are probably going to keep seeing it in the future.”
Uribe is the lead author of another recent study in Nature Climate Change that found that warmer temperatures and a lack of precipitation are making it harder for tropical forests to absorb CO2 from the atmosphere.
Uribe said the new study’s findings are “substantial” as they illustrate a positive feedback loop between climate change, drought, and water availability that could in turn lead to worsening climate change.
“Prolonged and more frequent, intense droughts reduce the tropical forest ability to absorb carbon, leading to higher concentrations of carbon in the atmosphere and further climate changes,” she said. “Moreover, we also have other human-induced disturbances like deforestation and forest degradation. These actions further impact our forests and climate, and we already know the consequences they bring. Despite this knowledge, we still lack sufficient efforts to prevent or slow down these negative effects.”
Banner image: Tropical forest in the Amazon. Image by eismannhans via Pixabay (Public domain).
Elizabeth Claire Alberts is a senior staff writer for Mongabay. Follow her on Twitter @ECAlberts.
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