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Trees in Australia's tropical rainforests have become the first worldwide by shifting from acting as a carbon sink to turning into a carbon emitter, due to rising heat extremes and arid environments.

The Tipping Point Identified

This crucial shift, which affects the trunks and branches of the trees but excludes the root systems, began approximately 25 years ago, according to new studies.

Trees naturally store carbon as they develop and release it when they decompose. Overall, tropical forests are considered carbon sinks – taking in more carbon dioxide than they release – and this absorption is assumed to increase with higher CO2 levels.

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

Study Insights

Roughly 25 years ago, tree trunks and branches in these forests turned into a carbon source, with more trees dying and inadequate regeneration, 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 other continents, and therefore it might serve as a future analog for what tropical forests will encounter in global regions.”

Worldwide Consequences

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

But should that be the case, the results could have significant implications for global climate models, CO2 accounting, and environmental regulations.

“This paper is the first time that this critical threshold 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 authority on climate science.

On a global scale, the share of carbon dioxide taken in 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 projections may underestimate global warming in the coming years. “Which is bad news,” he added.

Continued Function

Even though 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 take in additional CO2 would make emissions cuts “more challenging”, and require an even more rapid transition away from fossil fuels.

Data and Methodology

The analysis drew on a distinct collection of forest data dating back to 1971, including records tracking roughly 11,000 trees across 20 forest sites. It considered the carbon stored above ground, but excluded the gains and losses below ground.

An additional expert emphasized the value of gathering and preserving long term data.

“It was believed the forest would be able to absorb additional CO2 because [CO2] is increasing. But looking at these long term empirical datasets, we find that is incorrect – it enables researchers to compare models with actual data and improve comprehension of how these systems work.”