🔗 Share this article

Trees in Australia's tropical rainforests have become the first worldwide by shifting from acting as a carbon sink to turning into a carbon emitter, due to increasingly extreme temperatures and arid environments.

The Tipping Point Identified

This significant change, which impacts the trunks and branches of the trees but excludes the root systems, started around 25 years ago, as per new studies.

Trees naturally store carbon as they develop and release it upon decay and death. Generally, tropical forests are regarded as carbon sinks – absorbing more CO2 than they release – and this absorption is assumed to grow with higher CO2 levels.

However, nearly 50 years of data collected from tropical forests across northern Australia 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 insufficient new growth, according to the research.

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

“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 coming example for what tropical forests will experience in other parts of the world.”

Global Implications

A study contributor mentioned that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests worldwide, and additional studies are needed.

But if so, the results could have major consequences for international climate projections, CO2 accounting, and climate policies.

“This research is the initial instance that this tipping point of a switch from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not merely temporarily, but for two decades,” remarked an authority on climate science.

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

But should comparable changes – from absorber to emitter – were observed in other rainforests, climate forecasts may underestimate global warming in the future. “Which is bad news,” it was noted.

Ongoing Role

Although the equilibrium between gains and losses had changed, these forests were still playing an important role in absorbing carbon dioxide. But their reduced capacity to take in additional CO2 would make emissions cuts “more challenging”, and require an even more rapid transition away from fossil fuels.

Research Approach

This study utilized a unique set of forest data dating back to 1971, including records monitoring roughly 11,000 trees across 20 forest sites. It focused on the carbon stored in trunks and branches, but not the changes below ground.

An additional expert highlighted the importance of collecting and maintaining long term data.

“We thought the forest would be able to absorb additional CO2 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 ecosystems work.”