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Australian tropical rainforest trees have become the first worldwide by transitioning from acting as a carbon sink to turning into a carbon emitter, driven by increasingly extreme temperatures and arid environments.

The Tipping Point Identified

This crucial shift, which affects the stems and limbs of the trees but excludes the underground roots, started around 25 years ago, as per recent research.

Forests typically absorb carbon as they develop and emit it when they decompose. Overall, tropical forests are considered carbon sinks – taking in more carbon dioxide than they emit – and this uptake is expected to grow with rising atmospheric concentrations.

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

Research Findings

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

“This marks the initial rainforest of its kind to show this symptom of transformation,” stated the principal researcher.

“We know that the humid tropical regions in Australia occupy a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it might serve as a future analog for what tropical forests will experience in other parts of the world.”

Worldwide Consequences

One co-author mentioned that it remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests worldwide, and additional studies are required.

But if so, the results could have significant implications for international climate projections, carbon budgets, and climate policies.

“This paper is the first time that this tipping point of a switch from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not merely temporarily, but for two decades,” stated an expert in climate change science.

On a global scale, the share of carbon dioxide taken in by forests, trees, and plants has been quite stable over the last 20 to 30 years, which was expected to persist under numerous projections and policies.

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

Continued Function

Even though the equilibrium between growth and decline had shifted, these forests were still serving a vital function in soaking up CO2. But their reduced capacity to absorb extra carbon would make emissions cuts “more challenging”, and require 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 monitoring roughly 11,000 trees across numerous woodland areas. It focused on the carbon stored in trunks and branches, but not the changes below ground.

Another researcher highlighted the value of gathering and preserving extended datasets.

“We thought the forest would be able to store more carbon because [CO2] is increasing. But examining these decades of recorded information, we discover that is not the case – it allows us to compare models with actual data and better understand how these systems work.”