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Australian tropical rainforest trees have achieved a global first by transitioning from serving as a CO2 absorber to turning into a carbon emitter, driven by increasingly extreme temperatures and drier conditions.

Critical Change Identified

This significant change, which affects the stems and limbs of the trees but excludes the root systems, started around 25 years ago, according to recent research.

Forests typically absorb carbon during growth and release it upon decay and death. Overall, tropical forests are considered carbon sinks – absorbing more CO2 than they release – and this uptake is expected to grow with higher CO2 levels.

However, nearly 50 years of data gathered from tropical forests across northern Australia has revealed that this essential carbon sink may be at risk.

Study Insights

Approximately 25 years ago, tree trunks and branches in these forests turned into a carbon source, with increased tree mortality and insufficient new growth, according to the research.

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

“We know that the humid tropical regions in Australia occupy 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 encounter in other parts of the world.”

Worldwide Consequences

A study contributor mentioned that it is yet unclear whether Australia’s tropical forests are a harbinger for other tropical forests worldwide, and further research are required.

But if so, the results could have major consequences for international climate projections, CO2 accounting, and environmental regulations.

“This paper 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 merely temporarily, but for 20 years,” stated an expert in climate change science.

On a global scale, the share 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. “This is concerning,” he added.

Ongoing Role

Although the balance between growth and decline 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 require an accelerated transition away from fossil fuels.

Data and Methodology

This study utilized a unique set of forest data starting from 1971, including records monitoring roughly 11,000 trees across numerous woodland areas. It considered the carbon stored in trunks and branches, but not the gains and losses below ground.

An additional expert highlighted the value of collecting and maintaining long term data.

“It was believed the forest would be able to store more carbon because [CO2] is rising. But examining these long term empirical datasets, we discover that is incorrect – it enables researchers to compare models with actual data and improve comprehension of how these systems work.”