Queensland Tropical Forests Shift from Carbon Sink to Carbon Emitter in Global Milestone

Trees in Australia's tropical rainforests have achieved a global first by shifting from acting as a carbon sink to turning into a carbon emitter, due to rising heat extremes and drier conditions.

Critical Change Discovered

This significant change, which impacts the stems and limbs of the trees but does not include the underground roots, began approximately 25 years ago, as per new studies.

Forests typically absorb carbon as they develop and emit it upon decay and death. Overall, tropical forests are considered carbon sinks – absorbing more CO2 than they emit – and this absorption is expected to grow with rising atmospheric concentrations.

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

Research Findings

Approximately 25 years ago, tree stems and limbs in these forests became a net emitter, with increased tree mortality and insufficient new growth, according to the research.

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

“It is understood 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

A study contributor mentioned that it remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests worldwide, and additional studies are needed.

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

“This research is the initial instance that this tipping point of a switch from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not just for one year, but for two decades,” remarked an expert in climate change science.

On a global scale, the portion 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 numerous projections and strategies.

But should comparable changes – from absorber to emitter – were detected in other rainforests, climate projections may underestimate global warming in the coming years. “This is concerning,” it was noted.

Ongoing Role

Even though the equilibrium between growth and decline had changed, 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 necessitate an accelerated shift from carbon-based energy.

Research Approach

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

Another researcher highlighted the value of collecting and maintaining long term data.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But looking at 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.”