How can a small-scale deployment be achieved? Most stratospheric scientific studies of aerosol injection assume that the operating material is sulfur dioxide (SO2) gaseous, which contains 50% sulfur by mass. Another plausible option is hydrogen sulfide (H2S), which almost halves the mass requirement, although it is more dangerous to ground and aircrew than the SO2 and could therefore be eliminated from consideration. Carbon disulfide (CS2) gas reduces mass requirement by 40% and is generally less hazardous than SO2. It is also possible to use elemental sulfur, which is the safest and easiest to handle, but this would require an onboard combustion method before venting or using afterburner. No one has yet done the technical studies necessary to determine which of these sulfur compounds would be the best choice.
Using assumptions confirmed by Gulfstream, we estimate that any one of its G500/600 aircraft could transport approximately 10 kilotons of material per year over 15.5 kilometers. If CS high mass yield2 were used, a fleet of up to 15 aircraft could transport up to 100 kilotons of sulfur per year. Aged but functional used G650s cost around $25 million. Adding the cost of modification, maintenance, spare parts, salaries, fuel, materials and insurance, we project that the average total cost of a small-scale deployment over a decade would be d 'about 500 million dollars per year. A large-scale deployment would cost at least 10 times more.
How much is 100 kilotons of sulfur per year? This represents only 0.3% of current global annual emissions of sulfur pollution into the atmosphere. Its contribution to the health impact of particulate air pollution would be significantly less than a tenth of what it would be if the same amount were emitted to the surface. As for its impact on the climate, it represents approximately 1% of the sulfur injected into the stratosphere by the eruption of Mount Pinatubo in the Philippines in 1992. This well-studied event supports the assertion that no unknown effects with serious consequences would occur. .
At the same time, 100 kilotons of sulfur per year is not negligible: it would be more than twice the natural flux of sulfur from the troposphere to the stratosphere, in the absence of unusual volcanic activity. The cooling effect would be enough to delay global temperature rise by about a third of a year, a lag that would last as long as small-scale deployment was maintained. And because solar geoengineering is more effective at countering increasing extreme precipitation than increasing temperatures, its deployment would delay the increasing intensity of tropical cyclones by more than six months. These benefits are not insignificant for those most exposed to climate impacts (although none of these benefits would necessarily be apparent due to the natural variability of the climate system).
It is worth mentioning that our scenario of 100 kilotons per year is arbitrary. We define a small-scale deployment as one large enough to significantly increase the amount of aerosols in the stratosphere while being well below the level required to delay warming by a decade. With this definition, such a deployment could be several times larger or smaller than our example scenario.
Of course, no amount of solar geoengineering can eliminate the need to reduce the concentration of greenhouse gases in the atmosphere. At best, solar geoengineering is a complement to emissions reductions. But even the small-scale deployment scenario we consider here would be an important complement: over a decade, it would have a cooling effect about half as large as that of eliminating all EU emissions.
The policy of small-scale deployment
The small-scale deployment we have described here could serve several plausible scientific and technological goals. It would demonstrate storage, lofting and dispersion technologies for larger-scale deployment. If combined with an observation program, it would also assess monitoring capabilities. This would directly clarify how sulfate is transported in the stratosphere and how sulfate aerosols interact with the ozone layer. After a few years of such small-scale deployment, we would have a much better understanding of the scientific and technological obstacles to large-scale deployment.
At the same time, a small-scale deployment would present risks for the deployer. This could trigger political instability and invite retaliation from other countries and international bodies that would not react well to entities manipulating the planet's thermostat without global coordination and oversight. Opposition could come from a deep-seated aversion to environmental modification or from more pragmatic concerns that large-scale deployment would be detrimental to certain regions.
Deployers may be motivated by a wide range of considerations. Clearly, a state or coalition of states could conclude that solar geoengineering could significantly reduce climate risk and that such small-scale deployment would effectively balance the goals of pushing the world toward deployment. on a large scale and to minimize the risk of political disruption. backlash.