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Australian tropical rainforest trees have become the first worldwide by shifting from serving as a CO2 absorber to turning into a carbon emitter, driven by increasingly extreme temperatures and arid environments.

The Tipping Point Identified

This crucial shift, which impacts the stems and limbs of the trees but excludes the underground roots, started around 25 years ago, according to new studies.

Forests typically absorb carbon during growth and release it when they decompose. Generally, tropical forests are considered carbon sinks – absorbing more CO2 than they emit – and this absorption is expected to increase with higher CO2 levels.

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

Research Findings

Roughly 25 years ago, tree trunks and branches in these forests became a net emitter, with increased tree mortality and inadequate regeneration, according to the research.

“This marks the initial rainforest of its kind to show this symptom of change,” stated the lead author.

“It is understood that the humid tropical regions in Australia occupy a somewhat hotter, arid environment than tropical forests on other continents, and therefore it might serve as a coming example for what tropical forests will experience 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 additional studies are required.

But if so, the results could have significant implications for global climate models, CO2 accounting, 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 20 years,” remarked an expert in climate change science.

On a global scale, the portion of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the past few decades, which was expected to persist under numerous projections and strategies.

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

Ongoing Role

Even though the balance between gains and losses had shifted, these forests were still playing an important role in soaking up CO2. But their reduced capacity to take in additional CO2 would make emissions cuts “a lot harder”, and require an accelerated transition away from fossil fuels.

Research Approach

This study utilized a distinct collection of forest data starting from 1971, including records monitoring roughly 11,000 trees across 20 forest sites. 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.

“We thought the forest would be able to store more carbon because [CO2] is rising. But looking at these long term empirical datasets, we discover that is incorrect – it allows us to compare models with actual data and improve comprehension of how these ecosystems work.”