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Trees in Australia's tropical rainforests have become the first worldwide by transitioning from serving as a CO2 absorber to turning into a carbon emitter, due to rising heat extremes and drier conditions.

The Tipping Point Discovered

This crucial shift, which impacts the stems and limbs of the trees but does not include the underground roots, began approximately 25 years ago, according to new studies.

Forests typically absorb carbon during growth and emit it upon decay and death. Overall, tropical forests are considered carbon sinks – taking in more carbon dioxide than they emit – and this absorption is assumed to increase with higher CO2 levels.

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

Study Insights

Roughly 25 years ago, tree stems and limbs in these forests became a net emitter, with increased tree mortality and inadequate regeneration, as the study indicates.

“This marks the initial rainforest of its kind to display this sign of transformation,” stated the principal researcher.

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

Worldwide Consequences

A study contributor mentioned that it is yet unclear whether Australia’s tropical forests are a precursor for other tropical forests worldwide, and additional studies are needed.

But if so, the results could have significant implications for global climate models, carbon budgets, and environmental regulations.

“This paper is the first time 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 authority on climate science.

On a global scale, the portion of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the last 20 to 30 years, which was assumed to continue under numerous projections and policies.

But if similar shifts – from absorber to emitter – were detected in other rainforests, climate forecasts may understate heating trends in the future. “This is concerning,” it was noted.

Continued Function

Even though the balance between gains and losses 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 “more challenging”, and necessitate an even more rapid transition away from fossil fuels.

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 considered the carbon stored above ground, but not the gains and losses in soil and roots.

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

“We thought the forest would be able to absorb additional CO2 because [CO2] is rising. But examining these decades of recorded information, we discover that is incorrect – it allows us to compare models with actual data and improve comprehension of how these ecosystems work.”