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Australian tropical rainforest trees have become the first worldwide by transitioning from acting as a carbon sink to becoming a source of emissions, due to rising heat extremes and drier conditions.

Critical Change Discovered

This crucial shift, which impacts the stems and limbs of the trees but excludes the root systems, began approximately 25 years ago, according to recent research.

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

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

Study Insights

Roughly 25 years ago, tree trunks and branches in these forests became a net emitter, with more trees dying and insufficient new growth, according to the research.

“This marks the initial rainforest of its kind to display this sign of transformation,” commented the lead author.

“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 future analog for what tropical forests will encounter in other parts of the world.”

Worldwide Consequences

A study contributor mentioned that it remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests worldwide, and further research are required.

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

“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 merely temporarily, but for 20 years,” remarked an authority on climate science.

Worldwide, the share of carbon dioxide taken in by forests, trees, and plants has been relatively constant over the last 20 to 30 years, which was expected to persist under many climate models and policies.

But if similar shifts – from absorber to emitter – were observed in other rainforests, climate projections may underestimate global warming in the future. “Which is bad news,” he added.

Continued Function

Even though the balance between growth and decline had shifted, these forests were still serving a vital function in soaking up CO2. But their reduced capacity to take in additional CO2 would make emissions cuts “a lot harder”, and necessitate an accelerated shift from carbon-based energy.

Research Approach

This study utilized 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 in trunks and branches, but excluded the gains and losses below ground.

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

“It was believed the forest would be able to store more carbon because [CO2] is rising. But examining these decades of recorded information, we discover that is incorrect – it allows us to confront the theory with reality and better understand how these ecosystems work.”