Queensland Rainforest Trees Shift from Carbon Sink to Emissions Source in Global Milestone

Australian tropical rainforest trees have become the first worldwide by transitioning from serving as a CO2 absorber to becoming a source of emissions, driven by increasingly extreme temperatures and drier conditions.

The Tipping Point Identified

This crucial shift, which impacts the stems and limbs of the trees but does not include the root systems, began approximately a quarter-century back, as per recent research.

Forests typically absorb carbon during growth and emit it upon decay and death. Overall, tropical forests are regarded as carbon sinks – absorbing more CO2 than they release – and this uptake is assumed to grow with higher CO2 levels.

However, close to five decades of data collected from tropical forests across Queensland has revealed that this essential carbon sink may be at risk.

Research Findings

Roughly 25 years ago, tree trunks and branches in these forests became a net emitter, with increased tree mortality and insufficient new growth, as the study indicates.

“This marks the initial rainforest of its kind to show this symptom of change,” commented the lead author.

“It is understood that the humid tropical regions in Australia exist in a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it might serve as a coming example for what tropical forests will experience in other parts of the world.”

Worldwide Consequences

A study contributor noted that it is yet unclear whether Australia’s tropical forests are a precursor for other tropical forests globally, and additional studies are needed.

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

“This paper is the first time that this tipping point of a transition 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 authority on climate science.

On a global scale, the share 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 numerous projections and policies.

But should comparable changes – from sink to source – were observed in other rainforests, climate projections may underestimate global warming in the coming years. “This is concerning,” it was noted.

Continued Function

Even though the equilibrium between gains and losses had shifted, these forests were still serving a vital function in absorbing carbon dioxide. But their diminished ability to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an accelerated shift from carbon-based energy.

Data and Methodology

This study utilized a distinct collection of forest data dating back to 1971, including records tracking approximately 11,000 trees across 20 forest sites. It focused on the carbon stored above ground, but not the gains and losses below ground.

Another researcher highlighted the value 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 discover that is incorrect – it enables researchers to confront the theory with reality and better understand how these ecosystems work.”