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Trees in Australia's tropical rainforests have become the first worldwide by transitioning from serving as a CO2 absorber to becoming a source of emissions, due to rising heat extremes and arid environments.

Critical Change Discovered

This crucial shift, which affects the trunks and branches of the trees but does not include the root systems, began approximately 25 years ago, according to recent research.

Trees naturally store carbon as they develop and release it when they decompose. Overall, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they emit – and this absorption is expected to grow with rising atmospheric concentrations.

However, close to five decades of data collected from tropical forests across northern Australia has revealed that this vital carbon sink could be under threat.

Study Insights

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

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

“We know that the moist tropics 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 experience in global regions.”

Global Implications

A study contributor mentioned that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests globally, and additional studies 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 switch from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not just for one year, but for two decades,” stated 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 last 20 to 30 years, which was expected to persist under many climate models and strategies.

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

Ongoing Role

Even though the balance between growth and decline had shifted, these forests were still serving a vital function in absorbing carbon dioxide. But their diminished ability to absorb extra carbon would make emissions cuts “more challenging”, and necessitate an accelerated shift from carbon-based energy.

Research Approach

This study drew on a distinct collection of forest data dating back to 1971, including records tracking roughly 11,000 trees across numerous woodland areas. It focused on the carbon stored above ground, but excluded the gains and losses in soil and roots.

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

“It was believed the forest would be able to absorb additional CO2 because [CO2] is increasing. But looking at these long term empirical datasets, we find that is incorrect – it allows us to confront the theory with reality and improve comprehension of how these ecosystems work.”