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

Abstract

Abstract. The Greenland Ice Sheet (GrIS) will be losing mass at an accelerating pace throughout the 21st century, with a direct link between anthropogenic greenhouse gas emissions and the magnitude of Greenland mass loss. Currently, approximately 60 % of the mass loss contribution comes from surface melt and subsequent meltwater runoff, while 40 % are due to ice calving. Where most of the surface melt occurs (in the ablation zone), most of the energy for the surface melt is provided by absorbed shortwave fluxes, which could be reduced by solar geoengineering measures. However, so far very little is known about the potential impacts of an artificial reduction of the incoming solar radiation on the GrIS surface energy budget and the subsequent change in meltwater production. By forcing the regional climate model MAR with the latest CMIP6 future scenarios ssp245, ssp585 and associated G6solar experiment from the Earth System Model CNRM-ESM2-1, we evaluate the local changes due to the reduction of the solar constant on the projected GrIS surface mass balance (SMB) decrease. Overall, our results show that even in case of low mitigation greenhouse gas emissions scenario (ssp585), the Greenland surface mass loss can be brought in line with the medium mitigation emissions scenario (ssp245) by reducing the solar downward flux at the top of the atmosphere by ~40 W/m2 or ~1.5 % (using the G6solar experiment). In addition to reduce Global Warming in line with ssp245, G6solar also decreases the efficiency of surface meltwater production over the Greenland ice sheet by damping the well-known positive melt-albedo feedback which mitigates the projected Greenland ice sheet surface melt increase by 6 %. However, only more constraining geoengineering experiments than G6solar allows to maintain positive SMB till the end of this century without any reduction in our greenhouse gas emissions.

Identifying the sources of uncertainty in climate model simulations of solar radiation modification with the G6sulfur and G6solar Geoengineering Model Intercomparison Project (GeoMIP) simulations

“…Different spatial distributions of the aerosol layer, while yielding similar global values, might result in different ef- ficiency and would produce different responses of the surface climate (MacMartin et al, 2017;Kravitz et al, 2019;Visioni et al, 2020b). Reasons for a different aerosol distribution with similar injection locations and height of SO 2 can be the different dynamical features of the simulated stratosphere and/or differences in the aerosol microphysics schemes (Pitari et al, 2014;Niemeier et al, 2020;Franke et al, 2021) resulting in different aerosol growth, transport and sedimentation, as already shown for simulations of explosive volcanic eruptions (Marshall et al, 2018;Clyne et al, 2021). The response to the presence of the aerosols themselves can in turn produce differences in stratospheric dynamics, for instance, interacting with the quasi-biennial oscillation (Aquila et al, 2014;Richter et al, 2017), strengthening the tropical confinement of the aerosols (Niemeier and Schmidt, 2017;Visioni et al, 2018b).…”

“…Even when pursuing the same global mean temperature-oriented goal, it has been shown in simulations with CESM1(WACCM) that differences in the latitudinal (Kravitz et al, 2019 andseasonal (Visioni et al, 2020b) distribution of the aerosols can result in significant differences in surface climate. If different models simulate different distributions of the aerosols (as for the G4 experiment; Pitari et al, 2014) due to different stratospheric processes (both dynamical and chemical; Niemeier et al, 2020;Franke et al, 2021), the simulated surface climate would also be different. Furthermore, even given similar simulated aerosol distribution, the stratospheric response might differ due to differences in aerosol optics and in the radiative transfer calculation and in the representation of chemical processes in the stratosphere (i.e., if interactive chemistry is considered in the stratosphere; Franke et al, 2021) resulting in a different dynamical and ultimately surface response (Simpson et al, 2019;Jiang et al, 2019;Banerjee et al, 2021), which we discuss in Sect.…”

Meteorological effects and impacts of the 10 June 2021 solar eclipse over the British Isles, Iceland and Greenland

“…MAR was forced every 6 hours at its lateral boundaries by temperature, wind and specific humidity data from the European Centre for Medium Range Weather Forecasts (ECMWF) ERA5 reanalysis (Hersbach et al, 2020). The solar constant was reduced in the MAR radiative scheme (Fettweis et al, 2021) to take the effect of the eclipse into account, with a correction varying in space and time according to Figure 1. This methodology has previously been used to simulate meteorological effects of previous eclipses (Gray and Harrison, 2012) but is extended here to consider eclipse effects on the Greenland Ice Sheet.…”

Impact of the melt–albedo feedback on the future evolution of the Greenland Ice Sheet with PISM-dEBM-simple

“…Melt rates are calculated by PISM-dEBM-simple using periodic monthly temperature fields given by the climatological mean over the period 1971 to 1990 from the regional climate model MAR v3.11. MAR was forced with ERA reanalysis data (ERA-40 from 1958-1978 and ERA-5 after) (Kittel et al, 2021;Fettweis et al, 2021). In the warming experiments, scalar temperature anomalies are applied uniformly over the entire ice sheet.…”