🔗 Share this article Queensland Rainforest Trees Shift from Carbon Sink to Carbon Emitter in World First Australian tropical rainforest trees have become the first worldwide by shifting from acting as a carbon sink to turning into a carbon emitter, due to rising heat extremes and arid environments. Critical Change Identified This significant change, which affects the trunks and branches of the trees but excludes the root systems, started around 25 years ago, according to recent research. Trees naturally store carbon during growth and release it when they decompose. Generally, tropical forests are regarded as carbon sinks – absorbing more CO2 than they release – and this absorption is expected to increase with higher CO2 levels. However, close to five decades of data collected from tropical forests across northern Australia 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 inadequate regeneration, as the study indicates. “This marks the initial rainforest of its kind to show this symptom of transformation,” commented the lead author. “It is understood that the humid tropical regions in Australia exist in a slightly warmer, drier climate than tropical forests on different landmasses, and therefore it could act 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 precursor for other tropical forests globally, and additional studies are required. But should that be the case, the results could have significant implications for international climate projections, CO2 accounting, and environmental regulations. “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 identified clearly – not merely temporarily, but for two decades,” remarked an expert in climate change science. Worldwide, the share of carbon dioxide absorbed 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 if similar shifts – from absorber to emitter – were observed in other rainforests, climate projections may understate heating trends in the future. “Which is bad news,” he added. Ongoing Role Even though the balance between growth and decline had changed, 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 require an even more rapid shift from carbon-based energy. Research Approach The analysis utilized a unique set of forest data dating back to 1971, including records monitoring roughly 11,000 trees across numerous woodland areas. It focused on the carbon stored in trunks and branches, but not the gains and losses below ground. An additional expert emphasized the importance of gathering and preserving 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 better understand how these ecosystems work.”