🔗 Share this article

Trees in Australia's tropical rainforests 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.

The Tipping Point Identified

This significant change, which impacts the trunks and branches of the trees but does not include the root systems, began approximately a quarter-century back, according to recent research.

Forests typically absorb carbon during growth and emit it when they decompose. Overall, tropical forests are regarded as carbon sinks – absorbing more CO2 than they release – and this uptake is expected to grow with rising atmospheric concentrations.

However, close to five decades of data collected from tropical forests across Queensland has revealed that this essential carbon sink may be at risk.

Study Insights

Approximately 25 years ago, tree trunks and branches in these forests became a net emitter, with increased tree mortality and insufficient new growth, as the study indicates.

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

“It is understood that the humid tropical regions in Australia occupy a slightly warmer, drier climate 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 noted that it remains to be seen 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 major consequences for international climate projections, carbon budgets, and environmental regulations.

“This paper is the first time that this tipping point 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 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 relatively constant over the past few decades, which was assumed to continue under numerous projections and policies.

But should comparable changes – from sink to source – were observed in other rainforests, climate forecasts may underestimate global warming in the coming years. “Which is bad news,” he added.

Ongoing Role

Although the balance 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 accelerated transition away from fossil fuels.

Data and Methodology

This study drew on a distinct collection of forest data starting from 1971, including records tracking approximately 11,000 trees across numerous woodland areas. It considered the carbon stored in trunks and branches, but excluded the changes below ground.

Another researcher emphasized the importance of gathering and preserving extended datasets.

“We thought the forest would be able to absorb additional CO2 because [CO2] is rising. But looking at these long term empirical datasets, we find that is incorrect – it allows us to confront the theory with reality and better understand how these systems work.”