Optimal Climate Strategy with Mitigation, Carbon Removal, and Solar Geoengineering

TL;DR

This paper extends an integrated climate-economy model to include mitigation, carbon removal, and solar geoengineering, revealing that geoengineering can be used alongside mitigation early on, rather than only as a last resort.

Contribution

It introduces a novel extension of the DICE model to analyze the combined and temporal deployment of mitigation, CDR, and SG in climate policy.

Findings

SG is used alongside mitigation during peak CO2 levels.

CDR is employed after mitigation to reduce concentrations.

SG can be phased out after CDR reduces climate risks.

Abstract

Until recently, analysis of optimal global climate policy has focused on mitigation. Exploration of policies to meet the 1.5{\deg}C target have brought carbon dioxide removal (CDR), a second instrument, into the climate policy mainstream. Far less agreement exists regarding the role of solar geoengineering (SG), a third instrument to limit global climate risk. Integrated assessment modelling (IAM) studies offer little guidance on trade-offs between these three instruments because they have dealt with CDR and SG in isolation. Here, I extend the Dynamic Integrated model of Climate and Economy (DICE) to include both CDR and SG to explore the temporal ordering of the three instruments. Contrary to implicit assumptions that SG would be employed only after mitigation and CDR are exhausted, I find that SG is introduced parallel to mitigation temporary reducing climate risks during the era of peak CO2 concentrations. CDR reduces concentrations after mitigation is exhausted, enabling SG phasing out.