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# 3.4 Fake volcanoes

Injecting sulfate aerosols into the stratosphere to create fake volcanoes is a geoengineering solution which aims to reflect sunlight directly but as you studied in Session 3, they also have indirect effects on climate by influencing cloud formation.

“A paper in Science concluded that a Pinatubo-size [volcanic] eruption every few years would ‘offset much of the anthropogenic warming expected over the next century.’ … The 1992 NAS [National Academy of Sciences] report [Policy Implications of Global Warming] … raised the possibility of intentionally spreading sulfur dioxide in the stratosphere. … All that would be needed to produce a globe-changing effect is one-twentieth of 1 percent of current sulfur emissions, simply relocated to a higher point in the sky. … The task of reversing global warming boils down to a straightforward engineering problem: how to get thirty-four gallons per minute of sulfur dioxide into the stratosphere?

The answer: a very long hose.

… And it would be startlingly cheap. … this plan could be up and running in about three years, with a startup cost of $150 million and annual operating costs of$100 million.”

(Levitt and Dubner, 2009, pp. 176–96)

This chapter attracted widespread criticisms of oversimplifying the issues of climate change and geoengineering, under-emphasising the risks, misquoting a climate scientist, and making a number of factual errors and misleading statements. However, not only is it part of the history of the global conversation about engineering the climate (due to its huge popularity and criticism), but the method described in the extract – stratospheric sulfate aerosol injection, acting as a kind of artificial volcano – has been much discussed as a possible action to counter climate change.

• Having read the extract, would this method be limited in how much CO2 forcing it could offset (like urban albedo), or unlimited (like the solar shield)?

• Only a small amount of sulfur dioxide would be needed, meaning any amount of CO2 forcing could be offset.

Figure 6 illustrates some proposed methods of injecting aerosols into the stratosphere: a hose might be supported by a tall tower or suspended by balloons, although Robock et al. (2009) consider the aeroplanes and artillery shell methods more realistic for the near-term.

Figure 6 Proposed methods of stratospheric aerosol injection – artillery shells, a tall tower, aeroplanes and balloons – on a mountain, with supplies arriving by train.

Just like the urban albedo method, there are potential co-benefits. When aerosols scatter sunlight, it makes the light more diffuse. So although less sunlight reaches the surface (as is intended), more of that light comes from other directions than the Sun. This means more of it can reach into plant canopies, and the shadows are less sharp. Plants can photosynthesise more efficiently and this may lead to more growth.

• How might an increase in plant growth be a co-benefit for (a) humans and (b) counteracting global warming?

• An increase in plant growth may help agriculture to be more efficient, i.e. increases food security. It may also increase the amount of CO2 removed by vegetation from the atmosphere.

Sulfate aerosols can also lead to more spectacular sunsets (Figure 7).

Figure 7 Hong Kong sunset after the eruption of Pinatubo.

Another method that acts by intentionally changing the clouds is ocean spray.

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