Differing precipitation response between solar radiation management and carbon dioxide removal due to fast and slow components

Anton Laakso,Antti-Ilari Partanen,Stefan Liess,Dylan B Millet,Peter K Snyder

doi:10.5194/esd-11-415-2020

Anton Laakso, Antti-Ilari Partanen + Show 3 more

Open Access

https://doi.org/10.5194/esd-11-415-2020

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Abstract

Abstract. Solar radiation management (SRM) and carbon dioxide removal (CDR) are geoengineering methods that have been proposed to mitigate global warming in the event of insufficient greenhouse gas emission reductions. Here, we have studied temperature and precipitation responses to CDR and SRM with the Representative Concentration Pathway 4.5 (RCP4.5) scenario using the MPI-ESM and CESM Earth system models (ESMs). The SRM scenarios were designed to meet one of the two different long-term climate targets: to keep either global mean (1) surface temperature or (2) precipitation at the 2010–2020 level via stratospheric sulfur injections. Stratospheric sulfur fields were simulated beforehand with an aerosol–climate model, with the same aerosol radiative properties used in both ESMs. In the CDR scenario, atmospheric CO2 concentrations were reduced to keep the global mean temperature at approximately the 2010–2020 level. Results show that applying SRM to offset 21st century climate warming in the RCP4.5 scenario leads to a 1.42 % (MPI-ESM) or 0.73 % (CESM) reduction in global mean precipitation, whereas CDR increases global precipitation by 0.5 % in both ESMs for 2080–2100 relative to 2010–2020. In all cases, the simulated global mean precipitation change can be represented as the sum of a slow temperature-dependent component and a fast temperature-independent component, which are quantified by a regression method. Based on this component analysis, the fast temperature-independent component of the changed atmospheric CO2 concentration explains the global mean precipitation change in both SRM and CDR scenarios. Based on the SRM simulations, a total of 163–199 Tg S (CESM) or 292–318 Tg S (MPI-ESM) of injected sulfur from 2020 to 2100 was required to offset global mean warming based on the RCP4.5 scenario. To prevent a global mean precipitation increase, only 95–114 Tg S was needed, and this was also enough to prevent global mean climate warming from exceeding 2∘ above preindustrial temperatures. The distinct effects of SRM in the two ESM simulations mainly reflected differing shortwave absorption responses to water vapour. Results also showed relatively large differences in the individual (fast versus slow) precipitation components between ESMs.

Highlights

It is widely recognized that fast greenhouse gas (GHG) emission reductions, especially for carbon dioxide (CO2), are needed if ongoing global warming is to be slowed down
Global mean precipitation increased by 1.76 %–1.78 % under RCP4.5, below the CMIP5 multimodel mean (2.66 %)
We carried out simulations using two Earth system models, Max Planck Institute Earth System Model (MPI-ESM) and Community Earth System Model (CESM), with solar radiation management (SRM) based on stratospheric aerosols first simulated with the aerosol–climate model ECHAM-HAMMOZ

Summary

Introduction

It is widely recognized that fast greenhouse gas (GHG) emission reductions, especially for carbon dioxide (CO2), are needed if ongoing global warming is to be slowed down. The aim of the 2015 Paris Agreement was to maintain the global mean temperature increase within 2 ◦C of the preindustrial level and to pursue efforts to limit the mean increase to 1.5 ◦C (UNFCCC, 2015). Millar et al (2017) and Rogelj et al (2018) have shown that limiting warming to 1.5 ◦C is still possible, but it would require a fast and significant reduction in the use of fossil fuels complemented with carbon dioxide removal. Air quality legislation will likely lead to decreased cooling from anthropogenic aerosols, which might by itself be enough to increase global mean temperatures over the 1.5 ◦C target (Hienola et al, 2018)

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