A long-term study of protected rainforests in northeast Australia found that woody biomass has shifted from a carbon sink to a net carbon source. Tree mortality has doubled since around the year 2000, driven by extreme heat, drier air, drought, and more severe cyclones. The forests are losing more carbon than they absorb, even though they haven't been logged in nearly 40 years. Scientists used a dataset dating back to 1971 to track the same forest plots. The reversal was gradual and went unnoticed on the ground. The findings challenge assumptions about how reliable forest sinks are for offsetting emissions and meeting climate targets. If similar shifts occur in other tropical forests, global carbon budgets may need significant revision. The study highlights that even intact, protected ecosystems are vulnerable to climate stress. For carbon markets and policy, this raises questions about the permanence of forest-based offsets and the need for more conservative accounting of natural carbon sinks.
