🔗 Share this article

Trees in Australia's tropical rainforests have achieved a global first by shifting from serving as a CO2 absorber to becoming a source of emissions, due to increasingly extreme temperatures and drier conditions.

Critical Change Discovered

This significant change, which affects the trunks and branches of the trees but does not include the underground roots, began approximately 25 years ago, according to recent research.

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

However, nearly 50 years of data collected from tropical forests across Queensland has shown that this vital carbon sink could be under threat.

Study Insights

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

“This marks the initial rainforest of its kind to show this symptom of change,” commented the lead author.

“It is understood that the humid tropical regions in Australia occupy a slightly warmer, drier climate than tropical forests on other continents, and therefore it could act as a future analog for what tropical forests will encounter in global regions.”

Global Implications

One co-author noted that it is yet unclear whether Australia’s tropical forests are a precursor for other tropical forests worldwide, and additional studies are required.

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

“This research is the first time 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 20 years,” remarked an expert in climate change science.

On a global scale, the share of carbon dioxide taken in 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 if similar shifts – from absorber to emitter – were observed in other rainforests, climate forecasts may understate heating trends in the coming years. “Which is bad news,” it was noted.

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 take in additional CO2 would make emissions cuts “a lot harder”, and require an accelerated transition away from fossil fuels.

Research Approach

This study utilized a distinct collection of forest data starting from 1971, including records tracking approximately 11,000 trees across numerous woodland areas. It focused on the carbon stored above ground, but not the gains and losses in soil and roots.

An additional expert emphasized the importance of collecting and maintaining long term data.

“We thought the forest would be able to absorb additional CO2 because [CO2] is increasing. But examining these decades of recorded information, we discover that is incorrect – it enables researchers to confront the theory with reality and better understand how these systems work.”