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Trees in Australia's tropical rainforests have achieved a global first by transitioning from acting as a carbon sink to turning into a carbon emitter, due to increasingly extreme temperatures and drier conditions.

The Tipping Point Identified

This crucial shift, which affects the stems and limbs of the trees but does not include the underground roots, started around a quarter-century back, according to recent research.

Trees naturally store carbon during growth and emit it when they decompose. Overall, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they emit – and this uptake is expected to grow with rising atmospheric concentrations.

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

Research Findings

Approximately 25 years ago, tree stems and limbs in these forests became a net emitter, with increased tree mortality and inadequate regeneration, as the study indicates.

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

“We know that the humid tropical regions in Australia occupy a slightly warmer, drier climate than tropical forests on other continents, and therefore it could act as a coming example for what tropical forests will encounter in other parts of the world.”

Worldwide Consequences

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 needed.

But if so, the findings could have significant implications for international climate projections, carbon budgets, and environmental regulations.

“This research is the initial instance that this critical threshold 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.

Worldwide, the share of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the past few decades, which was expected to persist under numerous projections and policies.

But should comparable changes – from absorber to emitter – were detected in other rainforests, climate forecasts may underestimate global warming in the future. “This is concerning,” he added.

Continued Function

Even though the equilibrium between growth and decline had changed, these forests were still playing an important role in absorbing carbon dioxide. But their reduced capacity to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an accelerated shift from carbon-based energy.

Research Approach

The analysis drew on a distinct collection of forest data dating back to 1971, including records tracking roughly 11,000 trees across numerous woodland areas. It considered the carbon stored in trunks and branches, but not the gains and losses below ground.

An additional expert emphasized the value of gathering and preserving 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 discover that is incorrect – it allows us to confront the theory with reality and better understand how these systems work.”