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Australian tropical rainforest trees have become the first worldwide by shifting from serving as a CO2 absorber to becoming a source of emissions, driven by increasingly extreme temperatures and drier conditions.

The Tipping Point Identified

This crucial shift, which impacts the stems and limbs of the trees but excludes the root systems, began approximately 25 years ago, as per new studies.

Trees naturally store carbon during growth and release it upon decay and death. Generally, tropical forests are considered carbon sinks – absorbing more CO2 than they emit – and this absorption is assumed to grow with rising atmospheric concentrations.

However, close to five decades of data collected from tropical forests across northern Australia has shown that this vital carbon sink may be at risk.

Research Findings

Approximately 25 years ago, tree trunks and branches in these forests turned into a carbon source, with increased tree mortality and inadequate regeneration, according to the research.

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

“It is understood that the moist tropics in Australia exist in 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 experience in other parts of the world.”

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 additional studies are required.

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

“This paper is the first time that this tipping point of a switch from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not just for one year, but for 20 years,” remarked an expert in climate change science.

Worldwide, the portion of carbon dioxide taken in by forests, trees, and plants has been quite stable over the last 20 to 30 years, which was expected to persist under numerous projections and strategies.

But should comparable changes – from sink to source – were observed in other rainforests, climate forecasts may understate heating trends in the future. “This is concerning,” it was noted.

Continued Function

Even though the balance between growth and decline had shifted, these forests were still serving a vital function in soaking up CO2. But their reduced capacity to absorb extra carbon would make emissions cuts “a lot harder”, and necessitate an even more rapid shift from carbon-based energy.

Research Approach

The analysis utilized a distinct collection of forest data dating back to 1971, including records tracking roughly 11,000 trees across 20 forest sites. It focused on the carbon stored above ground, but not the gains and losses below ground.

An additional expert emphasized the value of gathering and preserving long term data.

“It was believed the forest would be able to absorb additional CO2 because [CO2] is rising. But looking at these decades of recorded information, we discover that is incorrect – it allows us to confront the theory with reality and improve comprehension of how these ecosystems work.”