Net-zero approaches must consider Earth system impacts to achieve climate goals

Commitments to net-zero carbon dioxide (CO2) or greenhouse gas (GHG) emissions targets now cover 88% of countries' emissions. Underlying the accounting behind net-zero frameworks is the assumption that emissions can be balanced with removals such that their net climate effect is zero. However, when considering the full climate impacts of CO2 emissions and removals, there are reasons to expect that the two are not equivalent in terms of their climate outcomes. We identify potential contributors to non-equivalence, including impermanence, biogeophysical and non-CO2 GHG effects, and argue that these non-equivalencies need to be accounted for to achieve climate goals. Given key uncertainties about the full climate impact of CO2 removal, it is prudent to prioritize emission reductions over removals. Underlying net-zero GHG accounting approaches is the assumption that emissions can be balanced by removals such that their net climate effect is zero. However, CO2 removals may not be equal and opposite to CO2 emissions in their climate impact, indicating the need to consider non-CO2 effects.