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Trees in Australia's tropical rainforests have become the first worldwide by shifting from serving as a CO2 absorber to becoming a source of emissions, driven by increasingly extreme temperatures and arid environments.

Critical Change Identified

This significant change, which impacts the stems and limbs of the trees but does not include the underground roots, began approximately a quarter-century back, according to recent research.

Trees naturally store carbon as they develop and emit it when they decompose. Generally, tropical forests are considered carbon sinks – absorbing more CO2 than they release – and this absorption is assumed to increase with rising atmospheric concentrations.

However, close to five decades of data gathered from tropical forests across northern Australia has revealed that this vital carbon sink may be at risk.

Study Insights

Approximately 25 years ago, tree stems and limbs in these forests turned into a carbon source, with more trees dying and insufficient new growth, according to the research.

“It’s the first tropical forest of its kind to show this symptom of change,” stated the principal researcher.

“It is understood that the moist tropics in Australia occupy a slightly warmer, drier climate than tropical forests on other continents, and therefore it could act as a coming example for what tropical forests will experience in other parts of the world.”

Global Implications

A study contributor mentioned that it is yet unclear whether Australia’s tropical forests are a precursor for other tropical forests globally, and further research are required.

But if so, the results could have major consequences for international climate projections, CO2 accounting, and environmental regulations.

“This paper is the first time that this tipping point of a transition from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not merely temporarily, but for 20 years,” stated an authority on climate science.

On a global scale, the portion of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the past few decades, which was assumed to continue under numerous projections and policies.

But if similar shifts – from sink to source – were detected in other rainforests, climate forecasts may understate heating trends in the coming years. “This is concerning,” he added.

Ongoing Role

Although the balance between growth and decline had shifted, these forests were still playing an important role in soaking up CO2. But their reduced capacity to take in additional CO2 would make emissions cuts “more challenging”, and require an even more rapid shift from carbon-based energy.

Data and Methodology

This study drew on a distinct collection of forest data starting from 1971, including records monitoring roughly 11,000 trees across numerous woodland areas. It focused on the carbon stored in trunks and branches, but not the changes in soil and roots.

Another researcher emphasized the importance of gathering and preserving extended datasets.

“It was believed the forest would be able to store more carbon because [CO2] is rising. But examining these long term empirical datasets, we discover that is incorrect – it allows us to confront the theory with reality and improve comprehension of how these ecosystems work.”