🔗 Share this article

Trees in Australia's tropical rainforests have achieved a global first by shifting from serving as a CO2 absorber to turning into a carbon emitter, due to increasingly extreme temperatures and arid environments.

Critical Change Identified

This crucial shift, which affects the trunks and branches of the trees but excludes the underground roots, started around 25 years ago, according to recent research.

Forests typically absorb carbon during growth and release it upon decay and death. Generally, tropical forests are considered carbon sinks – absorbing more CO2 than they emit – and this uptake is assumed to increase with higher CO2 levels.

However, close to five decades of data gathered from tropical forests across northern Australia has revealed that this essential carbon sink may be at risk.

Study Insights

Roughly 25 years ago, tree stems and limbs in these forests became a net emitter, with more trees dying and inadequate regeneration, as the study indicates.

“This marks the initial rainforest of its kind to display this sign of change,” stated the lead author.

“We know that the moist tropics in Australia occupy a slightly warmer, drier climate than tropical forests on other continents, and therefore it might serve as a coming example for what tropical forests will experience in other parts of the world.”

Global Implications

A study contributor noted that it is yet unclear whether Australia’s tropical forests are a harbinger for other tropical forests worldwide, and further research are needed.

But should that be the case, the results could have major consequences for global climate models, carbon budgets, and environmental regulations.

“This paper is the initial instance that this tipping point of a switch from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not just for one year, but for two decades,” stated an authority on climate science.

On a global scale, the portion 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 many climate models and strategies.

But if similar shifts – from absorber to emitter – were observed in other rainforests, climate forecasts may underestimate global warming in the future. “Which is bad news,” he added.

Ongoing Role

Although the balance between gains and losses had changed, these forests were still serving a vital function in soaking up CO2. But their diminished ability to absorb extra carbon would make emissions cuts “a lot harder”, and require an accelerated transition away from fossil fuels.

Data and Methodology

The analysis drew on a distinct collection 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 highlighted the importance of gathering and preserving extended datasets.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But looking at these decades of recorded information, we discover that is incorrect – it allows us to compare models with actual data and improve comprehension of how these systems work.”