The size and composition of residual emissions in integrated assessment scenarios at net-zero CO2

Abstract

Residual emissions are an important category of analysis in climate targets and scenarios, describing the emissions that would need to be compensated by carbon dioxide removal to reach net zero CO _2 . This article sheds light on the size and composition of residual emissions in integrated assessment modelling (IAM) scenarios at net-zero CO _2 , using the Intergovernmental Panel on Climate Change 6th assessment report (AR6) scenario database. I find that IAMs depict residual greenhouse gas emissions levels of 16 [12–26] GtCO _2 e/yr across below 1.5 °C, below 1.5 °C with overshoot, and below 2 °C scenarios—representing gross emissions reductions of 72 [55–78] % from 2020 to the point of net zero CO _2 . Emissions from livestock, agriculture, transport, waste and industrial processes remain most prevalent at net zero, with scenario averages tending to depict significantly lower reduction rates and higher residual emissions than those recently published in corporate net zero standards. Nonetheless, scenarios depict a wide range of outcomes across all of these ‘hard-to-abate’ sectors, with lower values characterised by demand-side shifts in the food and energy system, alongside the rapid electrification of end-use sectors and limits on CDR scaling. Current scenario reporting does not easily facilitate the calculation of gross emissions from the AR6 database, which would be a prerequisite to a more systematic exploration of the residual emissions frontier and its implications for climate policy.

Keywords

• climate change
• greenhouse gas emissions
• residual emissions
• carbon dioxide removal