The sustainability of carbon dioxide removal is critical to Paris' climate goals

Carbon dioxide removal is essential to achieving net zero emissions as any residual CO emissions need to be neutralized ₂ . The scientifically accepted definition of carbon dioxide removal requires that atmospheric CO be removed ₂ stored "permanently"; however, what is meant by durability remains unclear, and interpretations have varied from decades to millennia. Using a reduced-complexity climate model, we investigated here the effect of carbon dioxide removal with different storage lengths _CO2 . We found that storage time significantly affects whether net zero emissions achieve the desired temperature results. With typical 100-year storage, they lead to net zero CO emissions _{2 with residual emissions of 6 Gt CO 2} per year to an additional warming of 1.1 °C by 2,500 compared to permanent storage, putting internationally agreed temperature limits at risk. Our findings suggest that the storage period of CO ₂ less than 1000 years is insufficient to neutralize the remaining fossil CO emissions ₂ with net zero emissions. These results reinforce the principle that credible claims of neutralization by carbon dioxide removal within net zero require balancing emissions with removals of similar atmospheric residence time and storage, e.g. geological or biogenic. (Cyril Brunner , Zeke Hausfather & Reto Knutt, more at nature.com)