Queensland Rainforest Trees Shift from Carbon Sink to Carbon Emitter in Global Milestone

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

Critical Change Discovered

This crucial shift, which impacts the stems and limbs of the trees but does not include the underground roots, started around 25 years ago, as per new studies.

Trees naturally store carbon as they develop and release it when they decompose. Generally, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they release – and this uptake is expected to increase with rising atmospheric concentrations.

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

Study Insights

Approximately 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.

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

“It is understood that the humid tropical regions in Australia exist in a somewhat hotter, arid environment than tropical forests on different landmasses, and therefore it might serve as a coming example for what tropical forests will experience in global regions.”

Global Implications

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

But if so, the findings could have major consequences for international climate projections, CO2 accounting, and climate policies.

“This research 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 just for one year, but for 20 years,” stated an authority on climate science.

Worldwide, the portion of carbon dioxide absorbed by forests, trees, and plants has been quite stable 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 future. “Which is bad news,” he added.

Ongoing Role

Although the equilibrium between gains and losses had changed, 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.

Research Approach

This study utilized a unique set of forest data starting from 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 in soil and roots.

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

“We thought the forest would be able to store more carbon because [CO2] is rising. But examining these long term empirical datasets, we find that is incorrect – it enables researchers to compare models with actual data and improve comprehension of how these ecosystems work.”