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Australian tropical rainforest trees have become the first worldwide by transitioning from acting as a carbon sink to becoming a source of emissions, due to increasingly extreme temperatures and arid environments.

Critical Change Identified

This crucial shift, which impacts the trunks and branches of the trees but excludes the underground roots, started around a quarter-century back, according to new studies.

Forests typically absorb carbon as they develop and emit it when they decompose. Overall, tropical forests are regarded as carbon sinks – absorbing more CO2 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 vital carbon sink could be under threat.

Research Findings

Roughly 25 years ago, tree stems and limbs in these forests turned into a carbon source, with more trees dying and insufficient new growth, as the study indicates.

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

“We know that the moist tropics in Australia occupy a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it could act as a coming example for what tropical forests will experience in global regions.”

Worldwide Consequences

A study contributor mentioned that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests worldwide, and further research are required.

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

“This paper is the initial instance 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 expert in climate change science.

Worldwide, the share of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the last 20 to 30 years, which was expected to persist under many climate models and strategies.

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

Ongoing Role

Even though the equilibrium between gains and losses had shifted, these forests were still playing an important role in absorbing carbon dioxide. But their reduced capacity to take in additional CO2 would make emissions cuts “more challenging”, and require an accelerated shift from carbon-based energy.

Research Approach

This study utilized a distinct collection of forest data starting from 1971, including records tracking approximately 11,000 trees across numerous woodland areas. It considered the carbon stored above ground, but not the gains and losses below ground.

Another researcher emphasized the value of collecting and maintaining long term data.

“We thought the forest would be able to absorb additional CO2 because [CO2] is increasing. But looking at these decades of recorded information, we discover that is incorrect – it enables researchers to compare models with actual data and better understand how these systems work.”