🔗 Share this article

Australian tropical rainforest trees have achieved a global first by shifting from acting as a carbon sink to becoming a source of emissions, due to increasingly extreme temperatures and arid environments.

The Tipping Point Identified

This significant change, which affects the trunks and branches of the trees but excludes the root systems, started around 25 years ago, as per new studies.

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

However, close to five decades of data gathered from tropical forests across northern Australia has shown that this essential carbon sink could be under threat.

Research Findings

Approximately 25 years ago, tree trunks and branches in these forests turned into a carbon source, with increased tree mortality and inadequate regeneration, as the study indicates.

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

“It is understood that the moist tropics in Australia occupy a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it could act as a future analog for what tropical forests will encounter in other parts of the world.”

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 findings could have major consequences for global climate models, carbon budgets, and climate policies.

“This research is the initial instance that this critical threshold of a transition from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not merely temporarily, but for two decades,” stated an expert in climate change science.

On a global scale, the portion of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the last 20 to 30 years, which was expected to persist under numerous projections and policies.

But if similar shifts – from sink to source – were observed in other rainforests, climate forecasts may underestimate global warming in the future. “This is concerning,” it was noted.

Continued Function

Even though the equilibrium between growth and decline had shifted, these forests were still serving a vital function in absorbing carbon dioxide. 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 utilized a unique set of forest data dating back to 1971, including records tracking approximately 11,000 trees across numerous woodland areas. It focused on the carbon stored in trunks and branches, but excluded the changes below ground.

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

“We thought the forest would be able to store more carbon because [CO2] is rising. But examining these long term empirical datasets, we discover that is not the case – it enables researchers to compare models with actual data and better understand how these ecosystems work.”