🔗 Share this article

Australian tropical rainforest trees have become the first worldwide by transitioning from acting as a carbon sink to turning into a carbon emitter, due to rising heat extremes and drier conditions.

Critical Change Discovered

This significant change, which affects the stems and limbs of the trees but does not include the root systems, started around a quarter-century back, as per recent research.

Forests typically absorb carbon during growth and release it upon decay and death. Generally, tropical forests are regarded as carbon sinks – absorbing more CO2 than they emit – and this absorption is expected to grow with rising atmospheric concentrations.

However, close to five decades of data collected from tropical forests across Queensland has shown that this vital carbon sink could be under threat.

Study Insights

Approximately 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.

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

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

Global Implications

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

But should that be the case, the results could have significant implications for international climate projections, CO2 accounting, and environmental regulations.

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

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

But if similar shifts – from absorber to emitter – were observed in other rainforests, climate forecasts may underestimate global warming in the coming years. “This is concerning,” he added.

Ongoing Role

Even though the balance 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 “more challenging”, and necessitate an accelerated transition away from fossil fuels.

Data and Methodology

The analysis utilized a distinct collection of forest data starting from 1971, including records tracking approximately 11,000 trees across 20 forest sites. It considered the carbon stored above ground, but not the changes in soil and roots.

Another researcher highlighted the value of collecting and maintaining extended datasets.

“It was believed the forest would be able to store more carbon because [CO2] is rising. But examining these long term empirical datasets, we discover that is not the case – it allows us to confront the theory with reality and better understand how these ecosystems work.”