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Trees in Australia's tropical rainforests have achieved a global first by transitioning from serving as a CO2 absorber to turning into a carbon emitter, due to increasingly extreme temperatures and drier conditions.

Critical Change Discovered

This significant change, which affects the trunks and branches of the trees but does not include the underground roots, began approximately a quarter-century back, according to new studies.

Forests typically absorb carbon during growth and emit it when they decompose. Generally, tropical forests are considered carbon sinks – taking in more carbon dioxide than they release – and this absorption is expected to grow with rising atmospheric concentrations.

However, close to five decades of data collected from tropical forests across Queensland has shown that this essential carbon sink could be under threat.

Study Insights

Approximately 25 years ago, tree stems and limbs in these forests turned into a carbon source, with more trees dying 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.

“It is understood that the humid tropical regions in Australia occupy a somewhat hotter, arid environment than tropical forests on different landmasses, and therefore it could act as a coming example for what tropical forests will encounter in global regions.”

Worldwide Consequences

One co-author mentioned that it is yet unclear whether Australia’s tropical forests are a harbinger for other tropical forests globally, and further research are required.

But if so, the findings could have significant implications for international climate projections, CO2 accounting, and climate policies.

“This research 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 just for one year, but for 20 years,” stated an expert in climate change science.

Worldwide, the portion of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the past few decades, which was assumed to continue under numerous projections and policies.

But should comparable changes – from absorber to emitter – were observed in other rainforests, climate projections may understate heating trends in the coming years. “This is concerning,” he added.

Ongoing Role

Even though the balance between gains and losses had changed, these forests were still playing an important role in soaking up CO2. But their diminished ability to absorb extra carbon would make emissions cuts “more challenging”, and necessitate an accelerated shift from carbon-based energy.

Data and Methodology

This study utilized a distinct collection of forest data dating back to 1971, including records monitoring roughly 11,000 trees across numerous woodland areas. It focused on the carbon stored in trunks and branches, but excluded the changes in soil and roots.

Another researcher highlighted the value of gathering and preserving long term data.

“It was believed the forest would be able to store more carbon because [CO2] is rising. But looking at these long term empirical datasets, we find that is not the case – it allows us to confront the theory with reality and improve comprehension of how these ecosystems work.”