Current forest carbon offset buffer pools do not adequately insure against disturbance-driven carbon losses

Nature-based climate solutions in Earth’s forests could strengthen the land carbon sink and contribute to climate mitigation, but must adequately account for climate risks to the durability of carbon storage. Forest carbon offset protocols use a ‘buffer pool’ to insure against disturbance risks that may compromise durability. However, current buffer pool tools and allocations are not based on existing scientific data or models. Here, we use a tropical forest stand biomass model and an extensive set of long-term tropical forest plots to test whether current buffer pools are adequate to insure against observed disturbance regimes. We find that forest age and disturbance regime both influence necessary buffer pool sizes. In the vast majority of disturbance scenarios, current buffer pools are substantially smaller than required by carbon cycle science. Buffer pool estimates urgently need to be updated based on rigorous, open scientific datasets for nature-based climate solutions to succeed. Plain Language Summary Forests could contribute to climate mitigation through conservation and restoration activities. Carbon offsets are a widespread pathway to fund these nature-based climate solutions in forests, but must account for the risks to durability that forests face in a changing climate. Current carbon offset protocols have a buffer pool to insure against risk in different disturbance regimes, but the buffer pool contributions have not been tested with observed disturbance regimes and rigorous models. We tested these contributions using widespread tropical forest plot data and a carbon cycle model and find that the current buffer pool contributions are generally not adequate for most disturbance regimes. Our results highlight that better datasets, models, and tools are urgently needed in forest carbon offset protocols. Key points ### Competing Interest Statement The authors have declared no competing interest.