🔗 Share this article

Trees in Australia's tropical rainforests have achieved a global first by transitioning from serving as a CO2 absorber to turning into a carbon emitter, driven by rising heat extremes and arid environments.

The Tipping Point Discovered

This crucial shift, which impacts the stems and limbs of the trees but excludes the root systems, started around a quarter-century back, according to 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 release – and this uptake is assumed to increase with rising atmospheric concentrations.

However, close to five decades of data gathered from tropical forests across northern Australia has revealed that this essential 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 increased tree mortality and inadequate regeneration, according to the research.

“This marks the initial rainforest of its kind to display this sign of transformation,” commented the principal researcher.

“We know that the moist tropics in Australia occupy a somewhat hotter, arid environment than tropical forests on other continents, and therefore it could act as a future analog for what tropical forests will experience in other parts of the world.”

Global Implications

One co-author mentioned that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests globally, and further research are required.

But should that be the case, the findings could have major consequences for international climate projections, CO2 accounting, and climate policies.

“This research is the first time 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 20 years,” remarked an authority on climate science.

On a global scale, the share of carbon dioxide absorbed 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 should comparable changes – from absorber to emitter – were observed in other rainforests, climate projections may understate heating trends in the coming years. “Which is bad news,” he added.

Continued Function

Although the balance between growth and decline had shifted, 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 require an accelerated shift from carbon-based energy.

Data and Methodology

This study utilized a unique set of forest data dating back to 1971, including records monitoring approximately 11,000 trees across numerous woodland areas. 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 absorb additional CO2 because [CO2] is increasing. But examining these decades of recorded information, we discover that is not the case – it enables researchers to compare models with actual data and improve comprehension of how these systems work.”