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Australian tropical rainforest trees have become the first worldwide by shifting from serving as a CO2 absorber to turning into a carbon emitter, due to increasingly extreme temperatures and drier conditions.

Critical Change Discovered

This crucial shift, which affects the stems and limbs of the trees but excludes the root systems, started around a quarter-century back, according to new studies.

Forests typically absorb carbon during growth and emit it upon decay and death. Generally, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they emit – 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 revealed that this vital carbon sink may be at risk.

Study Insights

Approximately 25 years ago, tree trunks and branches in these forests turned into a carbon source, with more trees dying and inadequate regeneration, as the study indicates.

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

“It is understood that the moist tropics in Australia occupy a somewhat hotter, arid environment than tropical forests on different landmasses, and therefore it could act as a coming example for what tropical forests will experience in global regions.”

Worldwide Consequences

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

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

“This research is the initial instance that this critical threshold of a transition from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not just for one year, but for 20 years,” remarked an expert in climate change science.

Worldwide, the portion of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the last 20 to 30 years, 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 underestimate global warming in the coming years. “This is concerning,” it was noted.

Ongoing Role

Although the balance between gains and losses had changed, these forests were still playing an important role in absorbing carbon dioxide. But their diminished ability to absorb extra carbon would make emissions cuts “more challenging”, and necessitate an even more rapid shift from carbon-based energy.

Research Approach

The analysis drew on a unique set of forest data dating back to 1971, including records tracking approximately 11,000 trees across 20 forest sites. It focused on the carbon stored in trunks and branches, but not the changes in soil and roots.

An additional expert 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 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.”