🔗 Share this article Australian Rainforest Forests Shift from CO2 Absorber to Carbon Emitter in World First Trees in Australia's tropical rainforests have achieved a global first by shifting from acting as a carbon sink to becoming a source of emissions, due to increasingly extreme temperatures and drier conditions. The Tipping Point Identified This crucial shift, which affects the trunks and branches of the trees but does not include the underground roots, started around a quarter-century back, according to recent research. Forests typically absorb carbon during growth and release it upon decay and death. Generally, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they release – and this absorption is expected to grow with rising atmospheric concentrations. However, close to five decades of data collected from tropical forests across Queensland 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 more trees dying and inadequate regeneration, according to the research. “This marks the initial rainforest of its kind to display this sign of transformation,” stated the lead author. “It is understood that the moist tropics in Australia exist in a slightly warmer, drier climate 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.” Global Implications A study contributor noted that it remains to be seen whether Australia’s tropical forests are a harbinger for other tropical forests globally, and further research are required. But should that be the case, the findings could have major consequences for global climate models, carbon budgets, and climate policies. “This research 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 two decades,” stated an expert in climate change science. On a global scale, the portion of carbon dioxide absorbed by forests, trees, and plants has been relatively constant over the last 20 to 30 years, which was assumed to continue under many climate models and strategies. But if similar shifts – from sink to source – were observed in other rainforests, climate projections may understate heating trends in the future. “This is concerning,” it was noted. Continued Function Even though the equilibrium between gains and losses had shifted, these forests were still playing an important role in absorbing carbon dioxide. But their diminished ability to take in additional CO2 would make emissions cuts “a lot harder”, and necessitate an accelerated shift from carbon-based energy. Research Approach This study utilized a distinct collection of forest data dating back to 1971, including records monitoring roughly 11,000 trees across 20 forest sites. It considered the carbon stored in trunks and branches, but excluded the changes in soil and roots. An additional expert emphasized the importance of collecting and maintaining extended datasets. “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 find that is incorrect – it allows us to compare models with actual data and improve comprehension of how these ecosystems work.”