Durability of carbon dioxide removal is critical for Paris climate goals
Cyril Brunner, Zeke Hausfather, Reto Knutti
Abstract
Abstract Carbon Dioxide Removal is essential for achieving net zero emissions, as it is required to neutralize any residual CO 2 emissions. The scientifically recognized definition of Carbon Dioxide Removal requires removed atmospheric CO 2 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 CO 2 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 CO 2 emissions with 6 GtCO 2 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 CO 2 storage period of less than 1000 years is insufficient for neutralizing remaining fossil CO 2 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.