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Australian tropical rainforest trees have become the first worldwide by transitioning from acting as a carbon sink to becoming a source of emissions, driven by increasingly extreme temperatures and drier conditions.

Critical Change Discovered

This significant change, which affects the trunks and branches of the trees but excludes the root systems, started around a quarter-century back, according to recent research.

Trees naturally store carbon during growth and emit it when they decompose. Generally, tropical forests are regarded as carbon sinks – absorbing more CO2 than they emit – and this absorption is expected to grow with rising atmospheric concentrations.

However, close to five decades 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 became a net emitter, with more trees dying and inadequate regeneration, according to the research.

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

“It is understood that the humid tropical regions in Australia occupy 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 experience in other parts of the world.”

Global Implications

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 if so, the findings could have major consequences for global climate models, carbon budgets, and environmental regulations.

“This research is the initial instance that this tipping point of a transition from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not merely temporarily, but for two decades,” remarked 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 past few decades, which was assumed to continue under many climate models and policies.

But if similar shifts – from absorber to emitter – were observed in other rainforests, climate projections may underestimate global warming in the future. “Which is bad news,” it was noted.

Ongoing Role

Although the equilibrium between gains and losses had changed, these forests were still playing an important role in soaking up CO2. But their diminished ability to absorb extra carbon would make emissions cuts “more challenging”, 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 tracking roughly 11,000 trees across 20 forest sites. It focused on the carbon stored in trunks and branches, but excluded the gains and losses in soil and roots.

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

“We thought the forest would be able to absorb additional CO2 because [CO2] is rising. But examining these decades of recorded information, we discover that is not the case – it allows us to confront the theory with reality and improve comprehension of how these ecosystems work.”