🔗 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 crucial shift, which impacts the trunks and branches of the trees but does not include the underground roots, began approximately a quarter-century back, as per recent research.

Forests typically absorb carbon as they develop and emit it upon decay and death. Overall, tropical forests are regarded as carbon sinks – absorbing more CO2 than they emit – and this uptake is expected to grow with higher CO2 levels.

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

Study Insights

Approximately 25 years ago, tree trunks and branches 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 display this sign of change,” commented the lead author.

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

Global Implications

One co-author 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 if so, the findings 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 switch 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.

Worldwide, 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 policies.

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

Continued Function

Even though the balance between growth and decline had changed, these forests were still serving a vital function in absorbing carbon dioxide. But their diminished ability to take in additional CO2 would make emissions cuts “a lot harder”, and necessitate an accelerated transition away from fossil fuels.

Data and Methodology

This study drew on a unique set of forest data starting from 1971, including records monitoring roughly 11,000 trees across 20 forest sites. It considered the carbon stored above ground, but excluded the gains and losses in soil and roots.

An additional expert emphasized the importance of gathering and preserving long term data.

“It was believed 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 allows us to confront the theory with reality and improve comprehension of how these ecosystems work.”