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Trees in Australia's tropical rainforests have achieved a global first by shifting from acting as a carbon sink to becoming a source of emissions, driven by rising heat extremes and drier conditions.

The Tipping Point Discovered

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 upon decay and death. Overall, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they release – and this uptake is assumed to grow with rising atmospheric concentrations.

However, close to five decades of data collected from tropical forests across Queensland has shown that this vital carbon sink may be at risk.

Research Findings

Roughly 25 years ago, tree trunks and branches in these forests became a net emitter, 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 transformation,” stated the lead author.

“It is understood that the humid tropical regions in Australia occupy a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it could act as a coming example for what tropical forests will experience in other parts of the world.”

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 additional studies are required.

But should that be the case, the findings could have major consequences for international climate projections, CO2 accounting, and environmental regulations.

“This research is the initial instance that this tipping point of a transition from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not just for one year, but for two decades,” remarked an expert in climate change science.

On a global scale, the portion of carbon dioxide taken in by forests, trees, and plants has been quite stable over the past few decades, which was expected to persist under numerous projections and policies.

But should comparable changes – from absorber to emitter – were detected in other rainforests, climate forecasts may underestimate global warming in the coming years. “Which is bad news,” it was noted.

Continued Function

Even though the balance between gains and losses had shifted, 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 even more rapid transition away from fossil fuels.

Data and Methodology

This study drew on a distinct collection of forest data dating back to 1971, including records monitoring approximately 11,000 trees across numerous woodland areas. It considered the carbon stored in trunks and branches, but not the gains and losses in soil and roots.

An additional expert highlighted the value 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 not the case – it enables researchers to compare models with actual data and better understand how these ecosystems work.”