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Australian tropical rainforest trees have become the first worldwide by transitioning from serving as a CO2 absorber to turning into a carbon emitter, due to increasingly extreme temperatures and drier conditions.

Critical Change Discovered

This crucial shift, which impacts the trunks and branches of the trees but does not include the root systems, began approximately a quarter-century back, according to new studies.

Trees naturally store carbon as they develop and release it when they decompose. Generally, tropical forests are considered carbon sinks – taking in more carbon dioxide than they emit – and this absorption 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.

Study Insights

Roughly 25 years ago, tree stems and limbs in these forests became a net emitter, with more trees dying and inadequate regeneration, as the study indicates.

“It’s the first tropical forest of its kind to display this sign of transformation,” stated 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 could act as a future analog for what tropical forests will experience in global regions.”

Worldwide Consequences

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

But should that be the case, the results could have significant implications for global climate models, carbon budgets, and climate policies.

“This research is the initial instance that this tipping point 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.

Worldwide, the share of carbon dioxide taken in by forests, trees, and plants has been quite stable over the past few decades, which was assumed to continue under numerous projections and strategies.

But should comparable changes – from absorber to emitter – were observed in other rainforests, climate projections may understate heating trends in the coming years. “Which is bad news,” he added.

Continued Function

Although the equilibrium between gains and losses had changed, these forests were still playing an important role in absorbing carbon dioxide. But their diminished ability to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an even more rapid shift from carbon-based energy.

Data and Methodology

This study utilized a distinct collection of forest data starting from 1971, including records tracking approximately 11,000 trees across 20 forest sites. It focused on the carbon stored in trunks and branches, but excluded the gains and losses in soil and roots.

An additional expert highlighted the importance of collecting and maintaining long term data.

“We thought the forest would be able to store more carbon because [CO2] is increasing. But examining these long term empirical datasets, we find that is not the case – it enables researchers to confront the theory with reality and better understand how these ecosystems work.”