22 Aug 2022
22 Aug 2022
Status: this preprint is currently under review for the journal ESD.

Emit now, mitigate later? Earth system reversibility under overshoots of different magnitude and duration

Jörg Schwinger1, Ali Asaadi1, Norman Julius Steinert1, and Hanna Lee1,2 Jörg Schwinger et al.
  • 1NORCE Climate & Environment, Bjerknes Centre for Climate Research, Bergen, Norway
  • 2Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway

Abstract. Reversibility is, next to socio-economic feasibility and sustainability, key for assessing if carbon dioxide removal (CDR) could be considered to return the Earth system to a less dangerous state after a period of temperature overshoot above a level that is considered safe. Here, we use a state-of-the-art Earth system model that includes a representation of permafrost carbon to investigate the reversibility of the Earth system after overshoots of different duration and magnitude in idealized simulations. We find that atmospheric CO2 concentrations are slightly lower after an overshoot, compared to a reference simulation without overshoot, due to a near-perfect compensation of carbon losses from land by increased ocean carbon uptake during the overshoot periods. Many aspects of the Earth system including global average surface temperature, marine and terrestrial productivity, strength of the Atlantic meridional overturning circulation, surface ocean pH, surface O2 concentration, and permafrost extent are reversible on a centennial time scale except in the most extreme overshoot scenario considered in this study. Consistent with previous studies, we find irreversibility for permafrost carbon and deep ocean properties like sea water temperature, pH, and O2 concentrations. We do not find any indication of tipping points or self-reinforcing feedbacks that would put the Earth system on a significantly different trajectory after an overshoot. Hence, irreversibility might not be the main issue of CDR but rather the impacts and risks that would occur during the period of elevated temperatures during the overshoot.

Jörg Schwinger et al.

Status: open (until 07 Oct 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2022-39', Fortunat Joos, 29 Sep 2022 reply
  • RC2: 'Comment on esd-2022-39', Kirsten Zickfeld, 01 Oct 2022 reply

Jörg Schwinger et al.

Jörg Schwinger et al.


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Short summary
We test the reversibility the of the Earth system using idealized model simulations of overshoot pathways, where carbon dioxide is removed from the atmosphere to compensate for too large past and near term emissions. On a centennial time scale, we find a high degree of reversibility if the overshoot size remains small, and we do not find tipping points even for intense overshoots. We caution, however, that current ESMs are most likely not able to skillfully model tipping points in ecosystems.