Arctic cryosphere response in the Geoengineering Model Intercomparison Project G3 and G4 scenarios

Abstract

We analyzed output from the Geoengineering Model Intercomparison Project for the two most "realistic" scenarios, which use the representative concentration pathway of 4.5 Wm À2 by 2100 (RCP4.5) as the control run and inject sulfate aerosol precursors into the stratosphere. The first experiment, G3, is specified to keep RCP4.5 top of atmosphere net radiation at 2020 values by injection of sulfate aerosols, and the second, G4, injects 5 Tg SO 2 per year. We ask whether geoengineering by injection of sulfate aerosols into the lower stratosphere from the years 2020 to 2070 is able to prevent the demise of Northern Hemispere minimum annual sea ice extent or slow spring Northern Hemispere snow cover loss. We show that in all available models, despite geoengineering efforts, September sea ice extents still decrease from 2020 to 2070, although not as quickly as in RCP4.5. In two of five models, total September ice loss occurs before 2060. Spring snow extent is increased from 2020 to 2070 compared to RCP4.5 although there is still a negative trend in 3 of 4 models. Because of the climate system lag in responding to the existing radiative forcing, to stop Arctic sea ice and snow from continuing to melt, the imposed forcing would have to be large enough to also counteract the existing radiative imbalance. After the cessation of sulfate aerosol injection in 2070, the climate system rebounds to the warmer RCP4.5 state quickly, and thus, any sea ice or snow retention as a result of geoengineering is lost within a decade.

Response to marine cloud brightening in a multi-model ensemble

“…At the end of these 20 years, temperatures are almost back at the RCP4.5 levels. Previous GeoMIP publications investigating stratospheric aerosol injections (see, e.g., Berdahl et al, 2014) have noted a much faster warming in the rebound or termination period than in the RCP4.5 scenario, and this we find also here: for years 2070 to 2090 there is a warming of 0.007 K yr −1 for RCP4.5 and a warming of 0.040 K yr −1 for G4cdnc. In a GeoMIP study of stratospheric aerosol injections using three global climate models, Aswathy et al (2015) find that comparing the mean temperatures of the years 2050-2069 to 2020-2079 (where the latter is the termination period), there was a strong Arctic amplification when looking at the RCP4.5 scenario, but a weaker amplification in the climate engineering scenario.…”

Impact of idealized future stratospheric aerosol injection on the large‐scale ocean and land carbon cycles

“…Compared to other SRM modeling studies, such as Kravitz et al [], the projected cooler surface air temperature in our study is generally consistent with stronger cooling at high latitudes. Relative to the preindustrial state, we also show that SAI is less efficient in suppressing the warming in the polar regions [ Kravitz et al , ; Berdahl et al , ]. The regional precipitation response is more diverse among the different models, but globally, SAI is projected to decrease the precipitation [ Jones et al , ].…”

Assessing the controllability of Arctic sea ice extent by sulfate aerosol geoengineering

“…The spatial pattern of precipitation changes is highly uncertain as our results, by design, are based on just one climate model realization. Unfortunately, even globally uniform SRM interventions [e.g., Berdahl et al ., ; Ammann et al ., ] suffer regional side effects. Further, they typically fail to prevent the decline in ASI area because CO 2 has a greater amplification of Arctic temperature change than SRM [ Berdahl et al ., ; Lunt et al ., 2008].…”