🔗 Share this article Queensland Rainforest Forests Shift from Carbon Sink to Carbon Emitter in World First Australian tropical rainforest trees have achieved a global first by transitioning from acting as a carbon sink to turning into a carbon emitter, driven by rising heat extremes and drier conditions. The Tipping Point Identified This significant change, which impacts the trunks and branches of the trees but excludes the underground roots, began approximately 25 years ago, according to recent research. Trees naturally store carbon as they develop and release it upon decay and death. Overall, tropical forests are regarded as carbon sinks – taking in more carbon dioxide than they release – and this uptake is expected to grow with rising atmospheric concentrations. However, nearly 50 years of data gathered from tropical forests across Queensland has revealed that this essential carbon sink could be under threat. Study Insights Roughly 25 years ago, tree stems and limbs in these forests turned into a carbon source, with increased tree mortality and insufficient new growth, as the study indicates. “This marks the initial rainforest of its kind to show this symptom of change,” stated the principal researcher. “We know that the humid tropical regions in Australia exist in a slightly warmer, drier climate than tropical forests on other continents, and therefore it might serve as a future analog for what tropical forests will experience in global regions.” Worldwide Consequences A study contributor noted that it is yet unclear whether Australia’s tropical forests are a precursor for other tropical forests globally, and further research are required. But should that be the case, the findings could have major consequences for international climate projections, carbon budgets, and climate policies. “This research is the initial instance that this tipping point of a transition from a carbon sink to a carbon source in tropical rainforests has been definitively spotted – not merely temporarily, but for two decades,” remarked an authority on climate 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 numerous projections and policies. But should comparable changes – from absorber to emitter – were detected in other rainforests, climate projections may underestimate global warming in the coming years. “Which is bad news,” he added. Ongoing Role Even though the balance between growth and decline 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 “a lot harder”, and necessitate an even more rapid transition away from fossil fuels. Data and Methodology This study drew on a unique set of forest data dating back to 1971, including records monitoring roughly 11,000 trees across 20 forest sites. It focused on the carbon stored above ground, but excluded the changes in soil and roots. An additional expert highlighted the value of gathering and preserving extended datasets. “It was believed the forest would be able to absorb additional CO2 because [CO2] is increasing. But examining these long term empirical datasets, we discover that is not the case – it enables researchers to confront the theory with reality and improve comprehension of how these ecosystems work.”