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Trees in Australia's tropical rainforests have achieved a global first by shifting from serving as a CO2 absorber to turning into a carbon emitter, driven by rising heat extremes and arid environments.

Critical Change Identified

This crucial shift, which impacts the stems and limbs of the trees but excludes the underground roots, began approximately 25 years ago, as per recent research.

Trees naturally store carbon during growth and emit it when they decompose. Overall, tropical forests are regarded as carbon sinks – absorbing more CO2 than they emit – and this uptake is assumed to grow with rising atmospheric concentrations.

However, nearly 50 years of data gathered from tropical forests across Queensland has revealed that this vital carbon sink may be at risk.

Study Insights

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

“It’s the first tropical forest of its kind to display this sign of transformation,” stated the principal researcher.

“It is understood that the moist tropics in Australia exist in a somewhat hotter, arid environment than tropical forests on different landmasses, and therefore it might serve as a future analog for what tropical forests will experience in global regions.”

Worldwide Consequences

One co-author noted that it is yet unclear whether Australia’s tropical forests are a precursor for other tropical forests worldwide, and further research are needed.

But should that be the case, the results could have significant implications for global climate models, CO2 accounting, and environmental regulations.

“This research 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 20 years,” remarked an authority on climate science.

Worldwide, the share of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the past few decades, which was expected to persist under many climate models and strategies.

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

Continued Function

Although the equilibrium between growth and decline had changed, these forests were still playing an important role in absorbing carbon dioxide. But their reduced capacity to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an accelerated transition away from fossil fuels.

Data and Methodology

This study drew on a distinct collection of forest data dating back to 1971, including records tracking approximately 11,000 trees across numerous woodland areas. It focused on the carbon stored above ground, but not the changes below ground.

An additional expert highlighted the importance of gathering and preserving extended datasets.

“We thought the forest would be able to store more carbon because [CO2] is rising. But looking at these decades of recorded information, we find that is incorrect – it enables researchers to confront the theory with reality and improve comprehension of how these systems work.”