A new study published in Nature shows Australia’s tropical forests are shifting, with climate change driving a loss of their role as carbon sinks. Led by Hannah Carle of Western Sydney University, the team analysed repeated forest inventories from 1971 to 2019. Between 1971 and 2000, the forests stored about 0.62 Mg C ha−1 yr−1; by 2010–2019, they were losing roughly 0.93 Mg C ha−1 yr−1. Over the full study period, the authors estimate the sink declined by about 0.041 Mg C ha−1 yr−1 on average, with uncertainty ranges reported around those figures.
Rising tree mortality linked to hotter temperatures and more frequent climate extremes was identified as the principal cause. The paper reports no convincing evidence that elevated atmospheric CO2 has driven enough extra woody growth to offset these losses.
Severe weather is compounding the problem. In some plots, cyclone and storm damage produced biomass losses comparable to the accumulated effect of gradual climate‑driven mortality.
The researchers relied on long‑running permanent plots, high‑resolution climate records and causal‑inference methods to separate climate‑driven impacts from other factors, increasing confidence that the observed trends are climate related.
These results echo concerning signals from other tropical regions and suggest intact tropical forests may be approaching critical thresholds. If the pattern is widespread across the tropics, the global land carbon sink could weaken substantially.
The authors call for expanded long‑term monitoring, improved models that include extreme events and species vulnerabilities, and urgent cuts to greenhouse‑gas emissions to give forests a better chance of remaining carbon stores.
For more information: Carle, H., Bauman, D., Evans, M.N. et al. Aboveground biomass in Australian tropical forests is now a net carbon source. Nature 646, 611–618 (2025). https://doi.org/10.1038/s41586-025-09497-8.
