Durability of carbon dioxide removal is critical for Paris climate goals

Carbon Dioxide Removal is essential for achieving net zero emissions, as it is required to neutralize any residual CO₂ emissions. The scientifically recognized definition of Carbon Dioxide Removal requires removed atmospheric CO₂ to be stored “durably”; however, it remains unclear what is meant by durably, and interpretations have varied from decades to millennia. Using a reduced-complexity climate model, here we examined the effect of Carbon Dioxide Removal with varying CO₂ storage durations. We found that storage duration substantially affects whether net zero emissions achieve the desired temperature outcomes. With a typical 100-year storage duration, net zero CO₂ emissions with 6 GtCO₂ per year residual emissions result in an additional warming of 0.8 °C by 2500 compared to permanent storage, thus putting the internationally agreed temperature limits at risk. Our findings suggest that a CO₂ storage period of less than 1000 years is insufficient for neutralizing remaining fossil CO₂ emissions under net zero emissions. These results reinforce the principle that credible neutralization claims using Carbon Dioxide Removal in a net zero framework require balancing emissions with removals of similar atmospheric residence time and storage reservoir, e.g., geological or biogenic.