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Australian tropical rainforest trees have achieved a global first by shifting from serving as a CO2 absorber to turning into a carbon emitter, driven by increasingly extreme temperatures and arid environments.

The Tipping Point Discovered

This crucial shift, which impacts the trunks and branches of the trees but does not include the root systems, started around a quarter-century back, according to new studies.

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

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

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 show this symptom of change,” stated the principal researcher.

“We know that the humid tropical regions in Australia exist in a somewhat hotter, arid environment than tropical forests on other continents, and therefore it might serve as a future analog for what tropical forests will experience in global regions.”

Global Implications

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

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

“This research is the first time that this critical threshold 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,” remarked an authority on climate science.

On a global scale, the share of carbon dioxide absorbed by forests, trees, and plants has been relatively constant 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 coming years. “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 diminished ability to take in additional CO2 would make emissions cuts “a lot harder”, and require an even more rapid transition away from fossil fuels.

Data and Methodology

This study drew on a unique set of forest data dating back to 1971, including records tracking roughly 11,000 trees across 20 forest sites. It focused on the carbon stored above ground, but excluded the changes in soil and roots.

An additional expert emphasized the value of gathering and preserving long term data.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But examining these long term empirical datasets, we discover that is not the case – it enables researchers to confront the theory with reality and better understand how these systems work.”