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

The Tipping Point Discovered

This significant change, which impacts the trunks and branches of the trees but excludes the root systems, 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 – taking in more carbon dioxide than they release – and this absorption is assumed to increase with rising atmospheric concentrations.

However, close to five decades of data collected from tropical forests across Queensland has shown that this vital carbon sink could be under threat.

Study Insights

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

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

“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 could act as a coming example for what tropical forests will encounter in other parts of the world.”

Global Implications

One co-author mentioned that it remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests globally, and further research are needed.

But if so, the findings could have significant implications for international climate projections, 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 just for one year, but for 20 years,” remarked an authority on climate science.

Worldwide, the share 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 should comparable changes – from sink to source – were detected in other rainforests, climate forecasts may understate heating trends in the future. “Which is bad news,” it was noted.

Ongoing Role

Even though 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 “a lot harder”, and necessitate an even more rapid transition away from fossil fuels.

Data and Methodology

This study drew on a unique set of forest data dating back to 1971, including records monitoring roughly 11,000 trees across 20 forest sites. It considered the carbon stored above ground, but not the changes in soil and roots.

An additional expert highlighted the importance of collecting and maintaining long term data.

“It was believed the forest would be able to absorb additional CO2 because [CO2] is increasing. But examining these decades of recorded information, we discover that is not the case – it enables researchers to confront the theory with reality and better understand how these ecosystems work.”