# Will 100 gigagrams of sulphur be injected into the atmosphere, as part of a single geoengineering effort, by the end of 2023?

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Climate change geoengineering, defined by the United Kingdom’s Royal Society as “the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change” (Shepherd et al., 2009). Solar radiation management (SRM) supposes that deliberate addition of aerosol to the stratosphere could reduce climate risks by partially offsetting the radiative forcing from accumulating greenhouse gases. The deployment stratospheric sulfate aerosols have been proposed as a method to reflect more energy away from the planet, by increasing the planetary albedo, and thereby cool the planet, ameliorating some of the effects of increasing CO2 concentrations (Rasch et al., 2008).

According to (Rasch et al., 2008), sulphate aerosols have at least two cooling effects:

In the stratosphere they act to reflect incoming solar energy (the ‘aerosol direct effect’), but also act as cloud condensation nuclei, influencing the size of cloud droplets and the persistence or lifetime of clouds (the ‘aerosol indirect effect’) and thus the reflectivity of clouds.

Using the Mount Pinatubo eruption as an analogue, Crutzen, 2006 estimated a constant inflow of 5 teragrams (Tg) of Sulphur per year would be sufficient to balance the warming associated with a doubling of CO2. Rasch et al., 2008 suggested that 1.5 Tg S per year might suffice to balance the GHG warming. Finally, Robock et al., 2008 arrived at a figure of between 1.5 and 5 Tg S per year.

For reference, the net inflow of sulphur to the stratosphere is believed to be of the order of 100 gigagrams of per year when no volcanic eruptions occur (Rasch et al., 2008).

Will 100 gigagrams of sulphur be intentionally injected into the atmosphere, as part of a single geoengineering effort, by the end of 2023?

Resolution

This resolves positively when it is credibly reported that 100 gigagrams, i.e. $10^{11}$ grams, of sulphur is intentionally injected into the atmosphere in a single year as part of a single geoengineering effort, by the end of 2023. For the injection to qualify as a geoengineering effort, reporting must strong reveal evidence that that the parties responsible for the effort have the intent to bring about long-term effects on the regional or global climate.

For the purpose of this question, sulfur emissions are specified according to the equivalent weight of sulphur. For the purpose of this question we'll use the conversion of sulfur emissions and burdens found in (Rasch et al., 2008): 100 Gg S = 300 Gg of sulfur dioxide (SO₂) = 300 Gg of Sulfate (SO₄2) = 400 Gg aerosol particles (Gg = gigagram).

Moreover, a single geoengineering effort is defined as a project in which the relevant actors act on behalf of a various organisations (e.g. national government or research organisation) that coordinate in precise terms on the employed geoengineering methods as well as the the extent to, and the duration for which these are to be deployed.

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