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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 increasingly extreme temperatures and arid environments.

The Tipping Point Discovered

This crucial shift, which affects the trunks and branches of the trees but excludes the root systems, began approximately a quarter-century back, as per recent research.

Trees naturally store carbon during growth and emit it when they decompose. Overall, tropical forests are considered carbon sinks – taking in more carbon dioxide than they release – and this uptake is assumed to grow with rising atmospheric concentrations.

However, nearly 50 years of data collected from tropical forests across Queensland 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 increased tree mortality and insufficient new growth, according to the research.

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

“It is understood that the moist tropics in Australia exist in a slightly warmer, drier climate than tropical forests on other continents, 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 remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests worldwide, and additional studies are needed.

But if so, the results could have significant implications for global climate models, CO2 accounting, and climate policies.

“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 identified clearly – not just for one year, but for 20 years,” stated an authority on climate science.

On a global scale, the share of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the last 20 to 30 years, which was expected to persist under numerous projections and policies.

But if similar shifts – from absorber to emitter – were detected in other rainforests, climate projections may underestimate global warming in the coming years. “Which is bad news,” he added.

Continued Function

Even though the equilibrium between growth and decline had changed, these forests were still serving a vital function in absorbing carbon dioxide. But their diminished ability to take in additional CO2 would make emissions cuts “a lot harder”, and require an accelerated transition away from fossil fuels.

Data and Methodology

The analysis drew on a distinct collection of forest data starting from 1971, including records monitoring approximately 11,000 trees across numerous woodland areas. It considered the carbon stored in trunks and branches, but excluded the gains and losses in soil and roots.

Another researcher highlighted the importance of gathering and preserving extended datasets.

“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 not the case – it allows us to compare models with actual data and improve comprehension of how these systems work.”