Equivalence between carbon dioxide emissions and removals: A framework for net-zero accounting

The climatic effect of fossil-fuel derived CO₂ emissions is not necessarily equivalent to that of CO₂ removals. Asymmetry often exists with respect to the long-term radiative forcing effect of the net balance between emissions (that persist in the coupled atmosphere-land-ocean system for millennia) and removals (that may only persist on decadal to centennial timescales, particularly in nature-based solutions on land). To align emissions and removals for credible net-zero claims, we introduce the concept of carbon dioxide removal equivalents (CDRe), a metric that quantifies the radiative effect of CO₂ removals in proportion to the warming potential of CO₂ emissions. This metric can be combined with traditional CO₂ equivalents (CO₂e) for emissions to obtain the net climate effect of greenhouse gas emissions and CO₂ removals in a unified net-zero accounting framework.