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Australian tropical rainforest trees have become the first worldwide by transitioning from serving as a CO2 absorber to becoming a source of emissions, driven by increasingly extreme temperatures and drier conditions.

The Tipping Point Identified

This significant change, which impacts the trunks and branches of the trees but excludes the underground roots, started around 25 years ago, as per recent research.

Trees naturally store carbon as they develop and release it when they decompose. Generally, tropical forests are considered carbon sinks – absorbing more CO2 than they emit – and this absorption is assumed to increase with higher CO2 levels.

However, nearly 50 years of data collected from tropical forests across Queensland has shown that this essential carbon sink could be under threat.

Study Insights

Approximately 25 years ago, tree trunks and branches in these forests turned into a carbon source, with increased tree mortality and insufficient new growth, according to the research.

“This marks the initial rainforest of its kind to display this sign of change,” commented the principal researcher.

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

Worldwide Consequences

One co-author mentioned that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests globally, 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 research is the first time 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,” stated an authority on climate science.

On a global scale, the portion of carbon dioxide taken in by forests, trees, and plants has been quite stable over the past few decades, which was assumed to continue under many climate models and strategies.

But if similar shifts – from sink to source – were detected in other rainforests, climate projections may understate heating trends in the coming years. “Which is bad news,” it was noted.

Continued Function

Even though the balance between gains and losses had shifted, 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 utilized a unique set of forest data dating back to 1971, including records tracking approximately 11,000 trees across 20 forest sites. It considered the carbon stored above ground, but not the gains and losses below ground.

Another researcher highlighted the importance of gathering and preserving 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 discover that is incorrect – it allows us to compare models with actual data and better understand how these systems work.”