Future volcanic eruptions shift the timing of net-zero emissions

Volcanic eruptions are inevitable, unpredictable, and impact climate globally. During outbreaks, volcanic aerosols enter the stratosphere, modifying the planetary energy balance. How eruptions affect biosphere carbon uptake is unclear, as including the possible forcing trajectories in climate model projections is computationally expensive. Here, we show realistic future volcanic forcing increases projected regional temperature variability for the overshoot scenario SSP5-3.5-OS and adds uncertainty to biosphere carbon sink capacity estimates. We use intermittent eruption trajectories to derive 300 estimates of future climate and biosphere productivity from a computationally efficient, regionally explicit simulator. Global mean temperature pathway uncertainty relative to the internal component is, on average, 0.32°C (+89%) larger with intermittent forcing. Propagating this uncertainty into net carbon uptake through shared variances between climatic drivers and the biosphere’s response increases regional uncertainty by up to 34% of internal variability. Regionally, uncertainty in annual temperature is increased by 50%+ for half of the world’s population. Effects aggregate globally, potentially delaying or advancing net-zero emissions and planetary temperature stabilization.