🔗 Share this article

Trees in Australia's tropical rainforests have achieved a global first by transitioning from serving as a CO2 absorber to becoming a source of emissions, driven by rising heat extremes and drier conditions.

The Tipping Point Identified

This significant change, which affects the trunks and branches of the trees but excludes the root systems, began approximately 25 years ago, according to new studies.

Forests typically absorb carbon as they develop and emit it upon decay and death. Generally, tropical forests are considered carbon sinks – taking in more carbon dioxide than they release – and this uptake is expected to grow with higher CO2 levels.

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

Research Findings

Approximately 25 years ago, tree stems and limbs in these forests turned into a carbon source, with more trees dying and insufficient new growth, as the study indicates.

“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 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 is yet unclear whether Australia’s tropical forests are a harbinger for other tropical forests worldwide, and additional studies are required.

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 definitively spotted – not just for one year, but for two decades,” remarked an expert in climate change science.

On a global scale, the share of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the past few decades, which was assumed to continue under numerous projections and strategies.

But should comparable changes – from sink to source – were detected in other rainforests, climate projections may underestimate global warming in the future. “This is concerning,” he added.

Ongoing Role

Even though the balance between growth and decline had shifted, these forests were still serving a vital function in absorbing carbon dioxide. But their reduced capacity to take in additional CO2 would make emissions cuts “a lot harder”, and necessitate an even more rapid shift from carbon-based energy.

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 numerous woodland areas. It considered the carbon stored in trunks and branches, but not the gains and losses below ground.

An additional expert highlighted the value of gathering and preserving extended datasets.

“We thought the forest would be able to store more carbon because [CO2] is increasing. But examining these decades of recorded information, we find that is incorrect – it allows us to confront the theory with reality and improve comprehension of how these systems work.”