🔗 Share this article

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

Critical Change Discovered

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

Trees naturally store carbon during growth and release it when they decompose. Generally, tropical forests are regarded as carbon sinks – absorbing more CO2 than they release – and this uptake is assumed to increase with higher CO2 levels.

However, nearly 50 years of data gathered from tropical forests across northern Australia has revealed that this vital 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 more trees dying and inadequate regeneration, as the study indicates.

“It’s the first tropical forest of its kind to show this symptom of change,” stated the lead author.

“We know that the moist tropics 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

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 required.

But if so, the findings could have significant implications for global climate models, 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 identified clearly – not just for one year, but for 20 years,” remarked an expert in climate change science.

On a global scale, the portion of carbon dioxide taken in by forests, trees, and plants has been relatively constant over the past few decades, which was assumed to continue under many climate models and policies.

But should comparable changes – from absorber to emitter – were detected in other rainforests, climate projections may underestimate global warming in the future. “This is concerning,” he added.

Ongoing Role

Although the equilibrium between gains and losses had changed, these forests were still playing an important role in soaking up CO2. But their reduced capacity 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 unique set of forest data starting from 1971, including records tracking roughly 11,000 trees across numerous woodland areas. It focused on the carbon stored in trunks and branches, but not the changes below ground.

Another researcher highlighted the value of gathering and preserving long term data.

“We thought the forest would be able to absorb additional CO2 because [CO2] is increasing. But looking at these long term empirical datasets, we find that is incorrect – it allows us to confront the theory with reality and improve comprehension of how these systems work.”