Implications of temperature overshoot dynamics for climate and carbon dioxide removal policies in the DICE model

Wilfried Rickels,Jörg Schwinger

doi:10.1088/1748-9326/ac22c0

Abstract

Assessing climate policies that involve temporary overshoot of temperature targets requires an accurate representation of carbon cycle and climate dynamics. Here, we compare temperature overshoot climate policies obtained with the dynamic integrated climate–economy (DICE) integrated assessment model using two different climate-carbon cycle sub-models: first, the original DICE implementation, and second an implementation of the finite amplitude impulse response (FaIR) simple climate model. We analyze in a cost-effectiveness framework the minimum abatement and carbon dioxide removal costs for compliance against a (future) ceiling on temperatures. In our setup, the magnitude of the overshoot is not limited by temperature impacts, but simply by the temperature dynamics such that from a certain compliance date onwards a temperature ceiling cannot be exceeded anymore. We show that the rather sluggish temperature response and underestimation of carbon sinks in the most recent version of DICE implies that the additional future temperature change after a cessation of a given CO2 emission scenario is significantly overestimated compared to the zero emission commitments obtained with FaIR and complex earth system models. However, investigating climate policies which allow for a temporary temperature overshoot, this inertia translates into more than twice as high optimal carbon prices compared to FaIR and consequently in rather strict climate policies. For compliance with the 1.5 °C target from 2100 onward and non-CO2-warming of 0.2 °C, the mean optimal carbon prices in the year 2030 are 173USD/tCO2 and 56USD/tCO2 for DICE and FaIR, respectively. Still, the dynamics towards the target suggest that improved understanding of and accounting for (limited) reversibility of vulnerable Earth system components is required to derive appropriate overshoot climate policies.

Highlights

The dynamic integrated climate–economy (DICE) model (Nordhaus 1992, 2008, 2014, 2017, 2019) has been criticized for underestimating the economic impacts of climate change (Stern 2007, Burke et al 2015, Hänsel et al 2020)
The effect of the rather sluggish temperature response and underestimation of carbon sinks in the most recent version of DICE is demonstrated in figure 1: In the simulation where emissions abruptly cease following the consumption of the 1.5 ◦C CO2 budget, all DICE calibrations underestimate the initial carbon uptake by sinks before emissions cease compared to finite amplitude impulse response (FaIR) as a reference
We analyze climate policies with respect to global emissions abatement and carbon dioxide removal (CDR) deployment using the most recent DICE model and a version of DICE amended with the carbon cycle and climate dynamics represented by the FaIR-Geoffroy model

Summary

Introduction

The dynamic integrated climate–economy (DICE) model (Nordhaus 1992, 2008, 2014, 2017, 2019) has been criticized for underestimating the economic impacts of climate change (Stern 2007, Burke et al 2015, Hänsel et al 2020). The smaller carbon sink and sluggish temperature response in DICE compared to FaIR-Geoffroy translate into increased CO2 prices, e.g. in the year 2030 from 41 to 48 USD/tCO2 in optimal cost-benefit climate policies (for non-CO2-forcing as specified in DICE). These limitations of the carbon and climate system in DICE are in particular relevant in the context of ambitious temperature targets which are potentially achieved after a temporary temperature overshoot

Methods

Results

Discussion

Conclusion