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Australian tropical rainforest trees have achieved a global first by transitioning from serving as a CO2 absorber to becoming a source of emissions, driven by increasingly extreme temperatures and arid environments.

The Tipping Point Identified

This crucial shift, which affects the trunks and branches of the trees but does not include the underground roots, started around a quarter-century back, according to recent research.

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

However, nearly 50 years of data gathered from tropical forests across northern Australia has revealed that this vital carbon sink could be under threat.

Research Findings

Roughly 25 years ago, tree trunks and branches in these forests turned into a carbon source, with increased tree mortality and insufficient new growth, as the study indicates.

“It’s the first tropical forest of its kind to display this sign of change,” stated the principal researcher.

“We know that the moist tropics in Australia exist in a somewhat hotter, arid environment than tropical forests on other continents, and therefore it might serve as a coming example for what tropical forests will experience in global regions.”

Global Implications

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

But should that be the case, the results could have major consequences for global climate models, carbon budgets, 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 definitively spotted – not merely temporarily, but for two decades,” stated an authority on climate science.

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

But should comparable changes – from sink to source – were observed 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 growth and decline had shifted, these forests were still serving a vital function in soaking up CO2. 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

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 considered the carbon stored in trunks and branches, but excluded the changes in soil and roots.

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

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But looking at these long term empirical datasets, we discover that is not the case – it enables researchers to compare models with actual data and improve comprehension of how these ecosystems work.”