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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, driven by increasingly extreme temperatures and arid environments.

The Tipping Point Discovered

This significant change, which impacts the trunks and branches of the trees but does not include the root systems, started around a quarter-century back, as per new studies.

Forests typically absorb carbon during growth and emit it when they decompose. Overall, tropical forests are considered carbon sinks – taking in more carbon dioxide than they emit – and this absorption is assumed to increase with rising atmospheric concentrations.

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

Research Findings

Approximately 25 years ago, tree trunks and branches in these forests became a net emitter, with more trees dying and inadequate regeneration, as the study indicates.

“It’s the first tropical forest of its kind to display this sign of transformation,” commented the lead author.

“It is understood that the humid tropical regions in Australia exist in a slightly warmer, drier climate than tropical forests on other continents, and therefore it might serve as a coming example for what tropical forests will encounter in other parts of the world.”

Worldwide Consequences

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

But should that be the case, the findings could have significant implications for international climate projections, carbon budgets, and environmental regulations.

“This research 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 two decades,” remarked 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 policies.

But should comparable changes – from sink to source – were detected in other rainforests, climate projections may underestimate global warming in the coming years. “Which is bad news,” it was noted.

Continued Function

Although the equilibrium between gains and losses had shifted, these forests were still serving a vital function in absorbing carbon dioxide. But their diminished ability to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an accelerated shift from carbon-based energy.

Data and Methodology

The analysis 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 in trunks and branches, but excluded the changes in soil and roots.

An additional expert emphasized the importance of collecting and maintaining long term data.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But looking at these decades of recorded information, we find that is incorrect – it allows us to confront the theory with reality and better understand how these systems work.”