🔗 Share this article

Trees in Australia's tropical rainforests have become the first worldwide by transitioning from acting as a carbon sink to turning into a carbon emitter, driven by increasingly extreme temperatures and drier conditions.

Critical Change Discovered

This significant change, which impacts the trunks and branches of the trees but excludes the underground roots, started around a quarter-century back, as per new studies.

Trees naturally store carbon as they develop and release it upon decay and death. Generally, tropical forests are considered carbon sinks – taking in more carbon dioxide than they release – and this uptake is expected to increase with higher CO2 levels.

However, close to five decades of data collected from tropical forests across Queensland has shown that this vital carbon sink could be under threat.

Research Findings

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

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

“We know that the humid tropical regions in Australia exist in a somewhat hotter, arid environment than tropical forests on different landmasses, and therefore it might serve as a future analog for what tropical forests will experience in global regions.”

Global Implications

A study contributor 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 results could have major consequences for global climate models, carbon budgets, and climate policies.

“This paper is the initial instance that this critical threshold of a switch from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not merely temporarily, but for 20 years,” stated an authority on climate 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 policies.

But if similar shifts – from sink to source – were observed in other rainforests, climate projections may underestimate global warming in the coming years. “This is concerning,” he added.

Ongoing Role

Although the equilibrium 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 “more challenging”, and necessitate an even more rapid transition away from fossil fuels.

Data and Methodology

The analysis drew on a unique set of forest data dating back to 1971, including records tracking roughly 11,000 trees across numerous woodland areas. It focused on the carbon stored above ground, but not the changes below ground.

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

“We thought the forest would be able to store more carbon because [CO2] is increasing. But looking at these decades of recorded information, we find that is incorrect – it allows us to compare models with actual data and better understand how these systems work.”