Geo-engineering schemes have been proposed to alleviate the consequences of global warming by continuous injection of sulfur into the stratosphere. Volcanic eruptions in the past have shown that strongly enhanced sulfate aerosols in the stratosphere result in a higher planetary albedo, leading to surface cooling. However, model simulations show significant local temperature changes embedded in the global cooling as a result of geoengineering. Also large local precipitation changes, may occur in case of geoengineering. In addition to the impact on the tropospheric climate, the significant increase of stratospheric sulfate aerosol densities caused by geoengineering approaches enhances heterogeneous reactions in the stratosphere that lead to ozone loss. The potential for exceedingly high Arctic ozone depletion in the context of geo-engineering is known. On the other hand, decreasing halogen compounds in the atmosphere, brought about by the Montreal Protocol, result in a recovery of the ozone layer and lessen the potential impact of aerosols.
The sensitivity of in the stratosphere to a proposed geo-engineering scheme is presented for future halogen conditions. Based on results of the NCAR, Whole Atmosphere Community Climate Model (WACCM), the enhanced volcanic aerosol loading in the geo-engineering simulation result in a one-to two-fold increase of the chemical ozone depletion for the Northern Hemisphere due to chemical and dynamical changes. A significant increase of ozone depletion in the Arctic polar vortex up to the end of this century was estimated from observations, likely resulting in dangerous increase in UV radiation at the Earth's surface that harmful impacts the biosphere. Further, the recovery of the Antarctic ozone hole would be delayed by several decades in case of geoengineering using sulfate aerosols.