Would adding sulfur dioxide to the atmosphere have a global cooling effect?

Question

There is reasonable evidence to suggest that the Earth is warming. The most probable cause appears to be increased CO₂ in the atmosphere, which has been reasoned about for quite some time.

There appear to have been some volcanic eruptions in the 1200s that lead to a mini-ice age. The cause appears to be increased sulfur dioxide (S02) in the atmosphere.

Could we engineer this?

My question is: Would adding sulfur dioxide to the atmosphere have a global cooling effect?

Answer 1

There have been a range of studies on the issue published in Atmospheric Chemistry and Physics and other scientific journals.

The short answer is "yes." The longer answer is "yes, but...."

In Climatic impacts of stratospheric geoengineering with sulfate, black carbon and titania injection, Jones, et. al. (2016) note:

In this paper, we examine the potential climatic effects of geoengineering by sulfate, black carbon and titania injection against a baseline RCP8.5 scenario. We use the HadGEM2-CCS model to simulate scenarios in which the top-of-the-atmosphere radiative imbalance due to rising greenhouse gas concentrations is offset by sufficient aerosol injection throughout the 2020–2100 period. We find that the global-mean temperature is effectively maintained at historical levels for the entirety of the period for all three aerosol-injection scenarios, though there is a wide range of side-effects which are discussed in detail.

Those side-effects would vary with the size of the particles used and the method and location of atmospheric injection, but would include:

• Impacts on human health from increased particulates.
• Changes in surface albedo from particulate deposition.
• Changes in the amount and location of precipitation across the globe.
• Increased stratospheric warming.
• Changes in stratospheric ozone levels.

There would be no amelioration for other climate impacts such as ocean acidification.

It is therefore important to note that the safest possible solution to avoiding the sort of climate change instantiated by, e.g., Fig. 6a of this report is to effectively mitigate greenhouse-gas emissions.

Other issues not addressed by this physics-based paper include:

• The requirement for any geoengineering scheme to be maintained for decades or centuries.
• The need for a substantial industrial base to manufacture and distribute the particulates involved.
• The (presumed) need for an international body to manage the process and address political concerns such as the costs and benefits of the geoengineering; such as if the process was going to increase or reduce rainfall to a particular region.

Answer 2

SO2 is a gas in the atmosphere, which does not cool the atmosphere. However, SO2 oxidizes to H2SO4, which gets involved with aqueous chemistry and often leads to sulfate (SO4). Sulfate is an aerosol that will reflect sunlight (like many aerosols) and block energy input to the Earth. If you increase the amount of sunlight being reflected back to space (reducing the amount of sunlight absorbed by the surface of the Earth), there is a net cooling affect.

So, yes, adding sulfur dioxide will have a net cooling affect, since a lot of it will convert to sulfate. However, increasing sulfur dioxide in the troposphere is the equivalent of polluting the air, which leads to health problems and acid rain problems. If you could inject sulfates into the stratosphere (which a very explosive volcanic eruption can do) then it won't affect the air we breathe (or cause acid rain) nearly as much. The real solution, though, to global warming is to limit carbon emissions (e.g. GHGs) so that significant polar ice and snow pack can be retained and do its job of reflecting light back to space.

http://www.sciencedirect.com/science/article/pii/S0021850296000638 http://www4.ncsu.edu/~franzen/public_html/Poland/Poznan08a/Sulfur_Cycle.pdf https://en.wikipedia.org/wiki/Stratospheric_sulfate_aerosols_(geoengineering)

Answer 3

One of the issues with adding sulfur dioxide to the air is that it produces acid rain, which in the past has had a detrimental effect on forests. This was a major issue during the 1960s to 1990s and it is still an issue.

One area that was badly affected, and is still dealing with the effects of acid rain is the Black Forest.