“The warming of earth by the increasing concentrations of CO2 and other greenhouse gases is partially countered by some backscattering to space of solar radiation by the sulfate particles, which act as cloud condensation nuclei and thereby influence the micro-physical and optical properties of clouds, affecting regional precipitation patterns, and increasing cloud albedo” (Crutzen, 2006).
This form of geoengineering is inspired by observations of volcanic eruptions. By utilising this property of sulphate particles as a form of solar radiation management, we could to cool the planet and offset global warming. However it is important to consider some of the other properties of sulphur dioxide (SO2), which include acid rain, ozone depletion and significant health risks.
“SO2 can affect the respiratory system and the functions of the lungs, and causes irritation of the eyes. Inflammation of the respiratory tract causes coughing, mucus secretion, aggravation of asthma and chronic bronchitis and makes people more prone to infections of the respiratory tract. Hospital admissions for cardiac disease and mortality increase on days with higher SO2 levels. When SO2 combines with water, it forms sulfuric acid; this is the main component of acid rain which is a cause of deforestation.” (WHO, 2011).
The dangers of SO2 mean that there have been considerable efforts and legislation put in place to reduce emissions and this reduction in emissions has to some extent amplified global warming. The situation is something of Catch-22.
The side-effects of atmospheric sulphate injections could include changed precipitation patterns creating pressure on food and water resources, potentially aggravating the risk of famine and drought in areas of the developing world (Tuana et al., 2012)
Atmospheric sulphate injections would also do nothing to combat ocean acidification but would have a negative impact on the production of solar power due to the increase of diffuse light. So while Wigley (2006) stresses the importance of mitigation alongside solar radiation management it seems significant to note that this approach could diminish one carbon-free energy source.
Another impact would be a change in sky colour. Atmospheric sulphate injections would impact the Rayleigh Scattering. Cruzen (2006) describes this impact as “colorful sunsets and sunrises” but others have a less rose-tinted view.
There is a theory that the volcanic eruption of Krakatoa on August 27 1883, which resulted in “Magnificent fiery sunsets and sunrises”, inspired Edvard Munch’s iconic painting “The Scream”. Munch recounts his experience of his inspiration:
"I was walking along the road with two friends—then the Sun set—all at once the sky became blood red—and I felt overcome with melancholy. I stood still and leaned against the railing, dead tired—clouds like blood and tongues of fire hung above the blue-black fjord and the city. My friends went on, and I stood alone, trembling with anxiety. I felt a great, unending scream piercing through nature."
Image Source: Wikipedia.org
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