Quantifying and Comparing Effects of Climate Engineering Methods on the Earth System

Abstract

To contribute to a quantitative comparison of climate engineering (CE) methods, we assess atmosphere‐, ocean‐, and land‐based CE measures with respect to Earth system effects consistently within one comprehensive model. We use the Max Planck Institute Earth System Model (MPI‐ESM) with prognostic carbon cycle to compare solar radiation management (SRM) by stratospheric sulfur injection and two carbon dioxide removal methods: afforestation and ocean alkalinization. The CE model experiments are designed to offset the effect of fossil‐fuel burning on global mean surface air temperature under the RCP8.5 scenario to follow or get closer to the RCP4.5 scenario. Our results show the importance of feedbacks in the CE effects. For example, as a response to SRM the land carbon uptake is enhanced by 92 Gt by the year 2100 compared to the reference RCP8.5 scenario due to reduced soil respiration thus reducing atmospheric CO2. Furthermore, we show that normalizations allow for a better comparability of different CE methods. For example, we find that due to compensating processes such as biogeophysical effects of afforestation more carbon needs to be removed from the atmosphere by afforestation than by alkalinization to reach the same global warming reduction. Overall, we illustrate how different CE methods affect the components of the Earth system; we identify challenges arising in a CE comparison, and thereby contribute to developing a framework for a comparative assessment of CE.

Impact of Solar Radiation Modification on Allowable CO2 Emissions: What Can We Learn From Multimodel Simulations?

“…However, recent studies such as Eliseev (2012) or Keith et al (2017) suggest that SRM might be understood as a form of carbon dioxide removal (CDR) technique because of its impacts on the global carbon cycle. This statement is also supported by former studies (Eliseev, 2012;Govindasamy et al, 2002;Keller et al, 2014;Lauvset et al, 2017;Matthews & Caldeira, 2007;Muri et al, 2015;Sonntag et al, 2018) which suggest that SRM is likely to strengthen carbon uptake by both ocean and terrestrial ecosystems. This finding is also supported by the modeled response of the carbon cycle to major volcanic eruptions (Brovkin et al, 2010;MacMartin et al, 2016;Rothenberg et al, 2012;Tjiputra & Otterå, 2011).…”

Land-use emissions play a critical role in land-based mitigation for Paris climate targets

“…The net biophysical effect depends on location: the albedo effect tends to dominate at high latitudes, while the ET effect tends to dominate in the Tropics. A reversal of past deforestation should result in a net cooling effect 13 , 38 . When bioenergy crops are placed on pre-existing agricultural land, the biophysical impacts are small.…”

“…A second study estimates greenhouse gas removal equivalent to 0.6–2.0 GtCyr −1 based on potentials from afforestation/reforestation, avoided deforestation, natural forest management, forest plantations, fire management, and avoided woodfuel harvesting 5 . The CO 2 removal potential of forests also depends on the background climate and atmospheric CO 2 concentration 13 .…”

Global streamflow and flood response to stratospheric aerosol geoengineering

“…CaMa-Flood is able to reproduce relatively realistic flow patterns in complex river regions, such as deltas (Ikeuchi et al, 2015;Yamazaki et al, 2011Yamazaki et al, , 2013. CaMa-Flood has been extensively validated and applied to many regional-and global-scale hydrological studies (e.g., Pappenberger et al, 2012;Hirabayashi et al, 2013;Mateo et al, 2014;Ikeuchi et al, 2015Ikeuchi et al, , 2017Trigg et al, 2016;Zsótér et al, 2016;Emerton et al, 2017;Suzuki et al, 2018;Yamazaki et al, 2017).…”