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Australian tropical rainforest trees have achieved a global first by shifting from serving as a CO2 absorber to turning into a carbon emitter, due to increasingly extreme temperatures and drier conditions.

The Tipping Point Discovered

This crucial shift, which affects the stems and limbs of the trees but excludes the underground roots, began approximately 25 years ago, as per 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 release – and this absorption is expected to grow with higher CO2 levels.

However, close to five decades of data gathered from tropical forests across Queensland has shown that this vital carbon sink could be under threat.

Study Insights

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

“This marks the initial rainforest of its kind to display this sign of transformation,” commented the lead author.

“It is understood that the moist tropics in Australia occupy a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it might serve as a coming example for what tropical forests will experience in global regions.”

Worldwide Consequences

One co-author noted that it remains to be seen whether Australia’s tropical forests are a precursor for other tropical forests globally, and further research are required.

But if so, the results could have significant implications for international climate projections, CO2 accounting, 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 two decades,” stated an expert in climate change science.

Worldwide, the portion of carbon dioxide absorbed by forests, trees, and plants has been quite stable over the last 20 to 30 years, which was assumed to continue under many climate models and strategies.

But if similar shifts – from absorber to emitter – were observed in other rainforests, climate forecasts may understate heating trends in the future. “Which is bad news,” it was noted.

Continued Function

Although the balance between gains and losses had shifted, these forests were still playing an important role in soaking up CO2. But their diminished ability to take in additional CO2 would make emissions cuts “a lot harder”, and require an accelerated shift from carbon-based energy.

Data and Methodology

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

Another researcher highlighted the importance of gathering and preserving long term data.

“It was believed the forest would be able to store more carbon because [CO2] is increasing. But looking at these decades of recorded information, we discover that is not the case – it allows us to compare models with actual data and improve comprehension of how these systems work.”