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Australian tropical rainforest trees have become the first worldwide by transitioning from serving as a CO2 absorber to becoming a source of emissions, driven by increasingly extreme temperatures and arid environments.

Critical Change Discovered

This crucial shift, which impacts the trunks and branches of the trees but does not include the root systems, started around 25 years ago, as per recent research.

Forests typically absorb carbon as they develop and release it upon decay and death. Overall, tropical forests are considered carbon sinks – absorbing more CO2 than they emit – and this uptake is assumed to grow with higher CO2 levels.

However, nearly 50 years of data gathered from tropical forests across northern Australia has revealed that this vital carbon sink could be under threat.

Research Findings

Roughly 25 years ago, tree stems and limbs in these forests turned into a carbon source, with increased tree mortality and inadequate regeneration, according to the research.

“This marks the initial rainforest of its kind to display this sign of transformation,” commented the principal researcher.

“We know that the moist tropics in Australia occupy a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it might serve as a coming example for what tropical forests will encounter in global regions.”

Worldwide Consequences

One co-author noted that it remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests globally, and further research are required.

But if so, the results could have major consequences for global climate models, CO2 accounting, and climate policies.

“This paper is the initial instance that this critical threshold of a transition from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not just for one year, but for two decades,” stated an expert in climate change 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 expected to persist under numerous projections and strategies.

But should comparable changes – from sink to source – were detected in other rainforests, climate projections may understate heating trends in the coming years. “This is concerning,” it was noted.

Continued Function

Even though the balance between growth and decline had shifted, these forests were still playing an important role in soaking up CO2. But their diminished ability to take in additional CO2 would make emissions cuts “a lot harder”, and necessitate an accelerated shift from carbon-based energy.

Data and Methodology

The analysis drew on a unique set of forest data starting from 1971, including records tracking roughly 11,000 trees across 20 forest sites. It considered the carbon stored in trunks and branches, but excluded the changes in soil and roots.

Another researcher emphasized the value of collecting and maintaining extended datasets.

“We thought the forest would be able to absorb additional CO2 because [CO2] is increasing. But examining these decades of recorded information, we find that is incorrect – it enables researchers to confront the theory with reality and better understand how these ecosystems work.”