🔗 Share this article

Australian tropical rainforest trees have achieved a global first by transitioning from acting as a carbon sink to turning into a carbon emitter, driven by increasingly extreme temperatures and arid environments.

The Tipping Point Discovered

This crucial shift, which affects the trunks and branches of the trees but excludes the root systems, began approximately 25 years ago, as per recent research.

Trees naturally store carbon during growth and release it when they decompose. Overall, tropical forests are considered carbon sinks – absorbing more CO2 than they emit – and this absorption is assumed to grow with rising atmospheric concentrations.

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

Research Findings

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.

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

“It is understood that the moist tropics 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.”

Global Implications

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

But if so, the results could have significant implications for global climate models, carbon budgets, and climate policies.

“This paper is the initial instance that this tipping point of a transition from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not just for one year, 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 expected to persist under many climate models and strategies.

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

Ongoing Role

Even though 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 “more challenging”, and require an accelerated transition away from fossil fuels.

Data and Methodology

The analysis utilized a distinct collection of forest data starting from 1971, including records tracking roughly 11,000 trees across numerous woodland areas. It focused on the carbon stored above ground, but excluded the changes in soil and roots.

Another researcher emphasized the value of gathering and preserving extended datasets.

“We thought the forest would be able to store more carbon because [CO2] is rising. But examining these long term empirical datasets, we discover that is incorrect – it enables researchers to compare models with actual data and improve comprehension of how these ecosystems work.”