🔗 Share this article

Trees in Australia's tropical rainforests have achieved a global first by transitioning from acting as a carbon sink to becoming a source of emissions, due to increasingly extreme temperatures and arid environments.

Critical Change Identified

This significant change, which impacts the trunks and branches of the trees but does not include the root systems, began approximately 25 years ago, as per recent research.

Trees naturally store carbon as they develop and emit it upon decay and death. Overall, tropical forests are considered carbon sinks – taking in more carbon dioxide than they emit – and this absorption is assumed to grow with higher CO2 levels.

However, nearly 50 years of data gathered from tropical forests across Queensland has shown that this vital carbon sink may be at risk.

Study Insights

Roughly 25 years ago, tree stems and limbs in these forests became a net emitter, with more trees dying and inadequate regeneration, according to the research.

“It’s the first tropical forest of its kind to display this sign of transformation,” commented the lead author.

“It is understood that the humid tropical regions in Australia occupy a somewhat hotter, arid environment than tropical forests on other continents, and therefore it might serve as a future analog for what tropical forests will experience in other parts of the world.”

Worldwide Consequences

A study contributor mentioned that it is yet unclear whether Australia’s tropical forests are a precursor for other tropical forests worldwide, and further research are required.

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

“This paper is the first time that this critical threshold 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 two decades,” stated an authority on climate science.

Worldwide, the share of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the last 20 to 30 years, which was expected to persist under numerous projections and strategies.

But should comparable changes – from sink to source – were detected in other rainforests, climate forecasts may underestimate global warming in the coming years. “This is concerning,” he added.

Continued Function

Although the balance between gains and losses had shifted, these forests were still serving a vital function in absorbing carbon dioxide. But their reduced capacity to absorb extra carbon would make emissions cuts “more challenging”, and necessitate an even more rapid transition away from fossil fuels.

Research Approach

The analysis utilized a unique set of forest data dating back to 1971, including records monitoring approximately 11,000 trees across 20 forest sites. It focused on the carbon stored above ground, but excluded the gains and losses below ground.

An additional expert emphasized the value of gathering and preserving long term data.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But looking at these long term empirical datasets, we discover that is incorrect – it allows us to confront the theory with reality and improve comprehension of how these ecosystems work.”