Australian Rainforest Forests Shift from Carbon Sink to Emissions Source in Global Milestone

Trees in Australia's tropical rainforests have achieved a global first by transitioning from serving as a CO2 absorber to turning into a carbon emitter, due to increasingly extreme temperatures and arid environments.

Critical Change Discovered

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.

Trees naturally store carbon as they develop and release it when they decompose. Generally, tropical forests are considered 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 Queensland has shown that this essential carbon sink may be at risk.

Research Findings

Roughly 25 years ago, tree stems and limbs in these forests became a net emitter, with increased tree mortality and insufficient new growth, according to the research.

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

“It is understood that the moist tropics in Australia exist in a somewhat hotter, arid environment than tropical forests on different landmasses, and therefore it could act as a future analog for what tropical forests will experience in global regions.”

Worldwide Consequences

One co-author noted 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 significant implications for global climate models, carbon budgets, and environmental regulations.

“This paper is the initial instance 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 20 years,” remarked an authority on climate science.

Worldwide, the portion of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the past few decades, which was expected to persist under many climate models and strategies.

But should comparable changes – from sink to source – were detected in other rainforests, climate forecasts may understate heating trends in the future. “This is concerning,” he added.

Ongoing Role

Although the equilibrium between growth and decline had shifted, these forests were still playing an important role in soaking up CO2. But their reduced capacity to take in additional CO2 would make emissions cuts “more challenging”, and necessitate an even more rapid shift from carbon-based energy.

Research Approach

This study drew on a distinct collection of forest data starting from 1971, including records monitoring approximately 11,000 trees across numerous woodland areas. It considered the carbon stored in trunks and branches, but not the changes in soil and roots.

An additional expert highlighted the value of collecting and maintaining extended datasets.

“We thought the forest would be able to absorb additional CO2 because [CO2] is rising. But examining these long term empirical datasets, we discover that is not the case – it enables researchers to compare models with actual data and better understand how these systems work.”