Greenland Ice Sheet Response to Stratospheric Aerosol Injection Geoengineering

Abstract

The Greenland ice sheet is expected lose at least 90% of its current volume if ice sheet summer temperatures warm by around 1.8°C above pre-industrial. Geoengineering by stratospheric sulfate aerosol injection might slow Greenland ice sheet melting and sea level rise by reducing summer temperature and insolation; however, such schemes could also reduce precipitation and affect large-scale climate drivers such as the Atlantic Meridional Over-turning Circulation (AMOC). Earlier work found that AMOC increased under geoengineering and that might lead to greater mass loss from Greenland than under greenhouse gas forcing alone. We simulated Greenland ice sheet climates using four Earth system models running the stratospheric sulfate aerosol injection experiment GeoMIP G4 and the CMIP RCP4.5 and RCP8.5 greenhouse gas scenarios that were then used to drive the surface energy and mass balance model, SEMIC. Simulated runoff is 20% lower under G4 than RCP4.5, while under RCP8.5 it is 17% higher. The mechanism is through increased Arctic sea ice concentration and reduced humidity leading to surface cooling of the ablation zone. Reduced absorption of outgoing longwave radiation caused by hydrological cycle weakening dominates associated decreases in precipitation under geoengineering and stronger AMOC than under RCP4.5. An ice dynamics model simulates 15% lower ice losses under G4 than RCP4.5. Thus, total sea level rise by 2070 from the Greenland ice sheet under G4 geoengineering is about 15-20% lower than under the RCP4.5 scenario. Plain Language SummaryMass loss from the Greenland ice sheet is expected to raise sea levels by tens of centimeters this century and far more in the further future. Rising seas are one of the most damaging aspects of the warming climate, affecting hundreds of millions, and costing $ trillions by 2100, and geoengineering might be one approach that could be used against this threat. But the North Atlantic climate is a complex region where the flux of warm tropical waters is being reduced by greenhouse warming, which geoengineering would reverse. Hence, how Greenland would likely respond is a key factor in deciding the potential utility of doing geoengineering. We examine the impact of stratospheric aerosol geoengineering on both the surface ice sheet water runoff (which accounts for half of present-day ice loss) and the dynamic loss of ice from fast-flowing glaciers that are being accelerated by warming ocean currents (accounting for the other half). We find that aerosol injection equivalent to about ¼ Pinatubo volcanic eruption per year can slow mass loss from Greenland by 15-20% compared with greenhouse gas forcing alone, mainly due to reduced surface melting.

Mitigation of Arctic permafrost carbon loss through stratospheric aerosol geoengineering

“…The ESMs differ in very many ways and Table 1 lists only a few of them. Moore et al 36 found that 4 of the same models as used here also produce a similar spread of differences (RCP4.5-G4) in mass balance for Greenland as found for C release from permafrost. This results from combinations of reasons: differences in the sensitivities of ESMs to greenhouse gas and SAI forcing means that simulated changes in AMOC, seasonal sea ice, cloud cover, specific humidity and hence longwave radiative absorption and accumulation rates all differ.…”

“…Reversing the greenhouse gas forced Arctic amplification effect seen now in warming northern soils 4 . Furthermore, geoengineering mitigates against the greenhousegas induced weakening of the Atlantic meridional overturning circulation 34 , thus the mild climate conditions produced by the North Atlantic Drift in Northwestern Europe are maintained under SAI, but otherwise weakened under greenhouse gas forcing 35,36 . Moreover, the losses of permafrost C storage are unevenly distributed with depth ( Supplementary Fig.…”

“…the 15-40 Tg CH 4 year −1 estimates of current permafrost wetland CH 4 emissions 46 . Since climate under G4 would be drier than under RCP4.5 36,47 , assuming the same proportionate release of CH 4 under both scenarios might tend to minimize (RCP4.5-G4) differences, and so be regarded as a conservative estimate. Figure 4 shows the changes of permafrost CH 4 emissions, due to PCF under the RCP4.5 and G4 scenarios.…”

Review of Solar Geoengineering for the Developing World: A Discourse on the State of Research and the Effects on Policy and Livelihoods for Africa

“…While seen as a viable option to curbing the adverse effects of global warming, its relative impacts and risks are still generally unclear, making it particularly controversial (Barrett, 2014:249;Reynolds et al, 2017:10). A considerable number of studies have explored the potential of solar geoengineering in reducing temperature as well as keeping the global mean temperature below the IPCC 1.5 o C projection (Irvine et al, 2010;Kravitz et al, 2011Kravitz et al, , 2013Jones et al, 2018;Moore et al, 2019). Many others are sceptical about its practicability and application in terms of financial commitments, human and environmental security implications (Horton and Reynolds, 2016:440).…”

Brief Communication: Reduction of the future Greenland ice sheet surface melt with the help of solar geoengineering

“…Until now, the precise impact of such solar geoengineering measures on the future Greenland ice sheet surface melt remains highly uncertain because it was evaluated only with global models run at too coarse spatial resolution not resolving the ablation zone and using very simple snow models (Irvine et al, 2018;Moore et al;. As shown in Fettweis et al (2020), the polar regional climate models offer a unique opportunity to refine these estimates with a polar-oriented sophisticated physics, a full representation of the snow-atmosphere interactions as well as a spatial resolution adequate to explicitly resolve the narrow GrIS ablation zone .…”