🔗 Share this article

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

The Tipping Point Identified

This crucial shift, which impacts the stems and limbs of the trees but excludes the underground roots, started around 25 years ago, as per recent research.

Trees naturally store carbon during growth and emit it upon decay and death. Overall, tropical forests are regarded as carbon sinks – absorbing more CO2 than they release – and this uptake is assumed to increase with higher CO2 levels.

However, nearly 50 years of data gathered 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 became a net emitter, with more trees dying and inadequate regeneration, according to the research.

“It’s the first tropical forest of its kind to show this symptom of transformation,” commented the principal researcher.

“It is understood that the humid tropical regions in Australia exist in a somewhat hotter, arid environment than tropical forests on other continents, and therefore it might serve as a coming example for what tropical forests will encounter in other parts of the world.”

Worldwide Consequences

One co-author noted that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests globally, and further research are needed.

But if so, the findings could have significant implications for international climate projections, carbon budgets, and climate policies.

“This research is the first time 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,” stated an expert in climate change science.

Worldwide, the portion of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the past few decades, 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 understate heating trends in the future. “Which is bad news,” he added.

Continued Function

Even though the balance between gains and losses had shifted, these forests were still serving a vital function in soaking up CO2. But their diminished ability to absorb extra carbon would make emissions cuts “more challenging”, and necessitate an accelerated shift from carbon-based energy.

Research Approach

This study utilized a unique set of forest data dating back to 1971, including records monitoring roughly 11,000 trees across 20 forest sites. It considered the carbon stored in trunks and branches, but not the gains and losses below ground.

Another researcher emphasized the value of gathering and preserving long term data.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But examining these decades of recorded information, we discover that is incorrect – it enables researchers to compare models with actual data and better understand how these ecosystems work.”