🔗 Share this article

Australian tropical rainforest trees have become the first worldwide by shifting from serving as a CO2 absorber to becoming a source of emissions, due to rising heat extremes and drier conditions.

Critical Change Identified

This significant change, which impacts the trunks and branches of the trees but excludes the root systems, began approximately a quarter-century back, as per recent research.

Trees naturally store carbon as they develop and emit it when they decompose. Overall, tropical forests are regarded as carbon sinks – absorbing more CO2 than they emit – and this uptake is assumed to grow with rising atmospheric concentrations.

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

Research Findings

Roughly 25 years ago, tree stems and limbs 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 principal researcher.

“We know that the humid tropical regions in Australia occupy a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it might serve as a future analog for what tropical forests will experience in other parts of the world.”

Global Implications

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

But should that be the case, the results could have major consequences for global climate models, carbon budgets, and climate policies.

“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 merely temporarily, but for two decades,” stated an authority on climate science.

On a global scale, the share of carbon dioxide taken in by forests, trees, and plants has been quite stable over the last 20 to 30 years, which was expected to persist under many climate models and policies.

But should comparable changes – from absorber to emitter – were observed 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 shifted, these forests were still playing an important role in soaking up CO2. But their diminished ability to take in additional CO2 would make emissions cuts “more challenging”, and require an even more rapid shift from carbon-based energy.

Research Approach

This study 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 above ground, but excluded the changes below ground.

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

“We thought the forest would be able to absorb additional CO2 because [CO2] is rising. But examining these long term empirical datasets, we discover that is incorrect – it allows us to compare models with actual data and better understand how these ecosystems work.”