Implications of delayed actions in addressing carbon dioxide emission reduction in the context of geo-engineering

Carbon dioxide emissions need to be reduced well below current emissions if atmospheric concentrations are to be stabilised at a level likely to avoid dangerous climate change. We investigate how delays in reducing CO₂ emissions affect stabilisation scenarios leading to overshooting of a target concentration pathway. We show that if geo-engineering alone is used to compensate for the delay in reducing CO₂ emissions, such an option needs to be sustained for centuries even though the period of overshooting emissions may only last for a few decades. If geo-engineering is used for a shorter period, it has to be associated with emission reductions significantly larger than those required to stabilise CO₂ without overshooting the target. In the presence of a strong climate–carbon cycle feedback the required emission reductions are even more drastic.