Despite potential positive effects from SRM, there are also several concerns suggested by many studies.
Controversies over stratospheric aerosol injection
One of the widely discussed concerns include the side effects of stratospheric aerosol injection.
Impacts on regional climate
The idea of stratospheric aerosol injection has been initiated after analysing the effects of major volcanic eruptions such as Mt. Pinatubo eruption (1991), which cooled down the earth's temperature globally for few years without significant adverse impacts. However, later studies investigated that actually, there were major adverse effects following the Mt. Pinatubo eruption, suggested by Trenberth and Dai (2007):
After examining precipitation and streamflow records between 1950 and 2004, the study indicated that there has been a 'substantial decrease in precipitation over land and a record decrease in runoff and river discharge into the ocean' between October 1991 and September 1992 (Trenberth and Dai, 2007). Furthermore, it is also suggested that drought may arise as an adverse effect of geoengineering application.
Confining the geoengineering region
Even if it is possible to control the exact amounts of aerosols injecting into the atmosphere - preferably less than amounts injected by volcanic eruptions - some questions still remain for answers; for example, is it possible to 'geoengineer' the isolated regions such as the Arctic and will the application be confined there? (Robock, 2008) Also, will the engineers and scientists be able to predict all the (adverse) effects beforehand while the question of confined geoengineering is unresolved? The adverse impacts of stratospheric aerosol injection may or may not be worse than predicted, but current simulations using different climate models reveal reduced precipitation over wide regions leading to the possibility of drought.
Ozone depletion
Some scientists propose a threat of ozone depletion from stratospheric aerosol injection, since aerosol particles can serve as a surface for chemical reactions that may destroy the ozone layer of the Earth (Robock, 2008). If this happens, devastating effects on crops and natural flora will be massive.
Yet, potential of SRM exerting positive influence also exists
However, other studies such as Modak and Bala (2014) signify that aerosol injection with different latitudinal distribution may be effective in reducing the impacts of climate change and global warming, although uncertainties in the process of injection/ transportation itself and particle size evolution over time exist.
Even though there are lots of concerns raised for different SRM approaches, stratospheric aerosol injection seems to receive greater attention than others. It seems to me that further studies on adverse effects should continue to be researched, since it is better to know all the possible side effects that could happen before the actual application of SRM technologies; preventing before it cannot be reversed.
