Queensland Rainforest Forests Switch from CO2 Absorber to Carbon Emitter in World First

Australian tropical rainforest trees have become the first worldwide by shifting from serving as a CO2 absorber to turning into a carbon emitter, driven by rising heat extremes and arid environments.

Critical Change Identified

This significant change, which impacts the trunks and branches of the trees but excludes the root systems, began approximately 25 years ago, according to new studies.

Forests typically absorb carbon as they develop and release it when they decompose. Generally, tropical forests are regarded as carbon sinks – absorbing more CO2 than they release – and this absorption is expected to increase with higher CO2 levels.

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

Research Findings

Roughly 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.

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

“We know that the humid tropical regions 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 experience in other parts of the world.”

Global Implications

A study contributor noted that it is yet unclear 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 significant implications for international climate projections, carbon budgets, and climate policies.

“This paper is the first time that this critical threshold of a switch from a carbon sink to a carbon source in tropical rainforests has been identified clearly – not merely temporarily, but for 20 years,” stated 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 last 20 to 30 years, which was assumed to continue under many climate models and policies.

But if similar shifts – from sink to source – were detected in other rainforests, climate projections may underestimate global warming in the future. “Which is bad news,” he added.

Continued Function

Although the equilibrium between growth and decline had shifted, these forests were still serving a vital function in soaking up CO2. But their reduced capacity to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an even more rapid transition away from fossil fuels.

Data and Methodology

The analysis drew on a unique set of forest data dating back to 1971, including records tracking approximately 11,000 trees across numerous woodland areas. It focused on the carbon stored above ground, but excluded the gains and losses in soil and roots.

An additional expert highlighted the value of gathering and preserving extended datasets.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But looking at these decades of recorded information, we discover that is incorrect – it allows us to compare models with actual data and improve comprehension of how these ecosystems work.”