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

The Tipping Point Discovered

This significant change, which impacts the stems and limbs of the trees but does not include the underground roots, started around 25 years ago, as per recent research.

Forests typically absorb carbon during growth and emit it upon decay and death. Generally, tropical forests are considered carbon sinks – taking in more carbon dioxide than they release – and this uptake is assumed to increase with higher CO2 levels.

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

Research Findings

Roughly 25 years ago, tree stems and limbs in these forests turned into a carbon source, with more trees dying and insufficient new growth, as the study indicates.

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

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

Worldwide Consequences

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

But if so, the findings could have significant implications for international climate projections, CO2 accounting, and environmental regulations.

“This paper is the initial instance that this tipping point of a switch from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not merely temporarily, but for 20 years,” stated an expert in climate change science.

On a global scale, the portion of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the last 20 to 30 years, which was assumed to continue under many climate models and policies.

But if similar shifts – from absorber to emitter – were detected in other rainforests, climate projections may understate heating trends in the future. “Which is bad news,” he added.

Continued Function

Even though the equilibrium between gains and losses had shifted, these forests were still playing an important role in absorbing carbon dioxide. But their reduced capacity to absorb extra carbon would make emissions cuts “more challenging”, and necessitate an accelerated transition away from fossil fuels.

Data and Methodology

This study utilized a unique set of forest data starting from 1971, including records tracking roughly 11,000 trees across 20 forest sites. It focused on the carbon stored above ground, but excluded the changes below ground.

An additional expert emphasized the value of gathering and preserving extended datasets.

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