🔗 Share this article

Australian tropical rainforest trees have become the first worldwide by shifting from acting as a carbon sink to turning into a carbon emitter, due to rising heat extremes and drier conditions.

Critical Change Identified

This significant change, which affects the trunks and branches of the trees but does not include the underground roots, started around 25 years ago, according to new studies.

Forests typically absorb carbon during growth and emit it when they decompose. Generally, tropical forests are considered carbon sinks – absorbing more CO2 than they emit – and this absorption is expected to increase with higher CO2 levels.

However, close to five decades of data gathered from tropical forests across northern Australia has shown that this vital carbon sink may be at risk.

Research Findings

Roughly 25 years ago, tree stems and limbs in these forests became a net emitter, with more trees dying and insufficient new growth, as the study indicates.

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

“We know 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

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

But if so, the results could have significant implications for international climate projections, carbon budgets, and environmental regulations.

“This research is the first time 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 authority on climate science.

On a global scale, the portion of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the past few decades, which was expected to persist under numerous projections and strategies.

But if similar shifts – from absorber to emitter – were detected in other rainforests, climate forecasts may understate heating trends in the future. “Which is bad news,” it was noted.

Continued Function

Although the balance between growth and decline had shifted, these forests were still serving a vital function in soaking up CO2. But their reduced capacity to absorb extra carbon would make emissions cuts “more challenging”, and require an even more rapid transition away from fossil fuels.

Research Approach

This study utilized a unique set of forest data dating back to 1971, including records tracking roughly 11,000 trees across 20 forest sites. It focused on the carbon stored above ground, but not the gains and losses below ground.

An additional expert highlighted the importance of collecting and maintaining extended datasets.

“We thought the forest would be able to absorb additional CO2 because [CO2] is rising. But looking at these decades of recorded information, we find that is not the case – it enables researchers to confront the theory with reality and better understand how these systems work.”