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Australian tropical rainforest trees have become the first worldwide by transitioning from acting as a carbon sink to turning into a carbon emitter, driven by increasingly extreme temperatures and arid environments.

The Tipping Point Identified

This significant change, which affects the stems and limbs of the trees but does not include the underground roots, started around a quarter-century back, according to new studies.

Trees naturally store carbon as they develop and release it when they decompose. Generally, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they release – and this absorption is expected to grow 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 stems and limbs in these forests became a net emitter, with more trees dying and insufficient new growth, as the study indicates.

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

“It is understood that the humid tropical regions in Australia exist in a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it could act as a future analog for what tropical forests will encounter in global regions.”

Global Implications

One co-author noted that it is yet unclear whether Australia’s tropical forests are a precursor for other tropical forests worldwide, and further research are needed.

But if so, the results could have significant implications for international climate projections, carbon budgets, and climate policies.

“This research is the initial instance that this tipping point of a switch from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not just for one year, but for 20 years,” 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 relatively constant over the past few decades, which was assumed to continue under many climate models 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,” it was noted.

Continued Function

Even though the balance between growth and decline had changed, these forests were still serving a vital function in soaking up CO2. But their diminished ability to absorb extra carbon would make emissions cuts “more challenging”, and necessitate an accelerated transition away from fossil fuels.

Data and Methodology

This study drew on a distinct collection of forest data starting from 1971, including records monitoring approximately 11,000 trees across numerous woodland areas. It focused on the carbon stored above ground, but excluded the changes below ground.

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

“It was believed the forest would be able to absorb additional CO2 because [CO2] is increasing. But examining these decades of recorded information, we discover that is not the case – it allows us to compare models with actual data and improve comprehension of how these ecosystems work.”