How would possibly subscale deployment be completed? Most stratospheric scientific research of aerosol injection assume the operative materials is sulfur dioxide (SO2) gasoline, which is 50% sulfur by mass. One other believable choice is hydrogen sulfide (H2S), which cuts the mass requirement nearly in half, although it’s extra hazardous to floor and flight crews than SO2 and thus could be eradicated from consideration. Carbon disulfide (CS2) gasoline cuts the mass requirement by 40% and is usually much less hazardous than SO2. It’s also potential to make use of elemental sulfur, which is the most secure and best to deal with, however this is able to require a technique of combusting it on board earlier than venting or using afterburners. Nobody has but executed the engineering research required to find out which of those sulfur compounds could be the only option.
Utilizing assumptions confirmed with Gulfstream, we estimate that any of its G500/600 plane may loft about 10 kilotons of fabric per yr to fifteen.5 kilometers. If extremely mass-efficient CS2 had been used, a fleet of not more than 15 plane may carry up 100 kilotons of sulfur a yr. Aged however operable used G650s price about $25 million. Including in the price of modification, upkeep, spare elements, salaries, gasoline, supplies, and insurance coverage, we count on the common complete price of a decade-long subscale deployment could be about $500 million a yr. Massive-scale deployment would price not less than 10 occasions as a lot.
How a lot is 100 kilotons of sulfur per yr? It’s a mere 0.3% of present international annual emissions of sulfur air pollution into the ambiance. Its contribution to the well being impression of particulate air air pollution could be considerably lower than a tenth of what it might be if the identical quantity had been emitted on the floor. As for its impression on local weather, it might be about 1% of the sulfur injected within the stratosphere by the 1992 eruption of Mount Pinatubo within the Philippines. That well-studied occasion helps the assertion that no high-consequence unknown results would happen.
On the similar time, 100 kilotons of sulfur per yr isn’t insubstantial: it might be greater than twice the pure background flux of sulfur from the troposphere into the stratosphere, absent uncommon volcanic exercise. The cooling impact could be sufficient to delay international rise in temperature for a few third of a yr, an offset that will final so long as the subscale deployment was maintained. And since photo voltaic geoengineering is simpler at countering the rise in excessive precipitation than the rise in temperature, the deployment would delay the rising depth of tropical cyclones by greater than half a yr. These advantages are usually not negligible to these most in danger from local weather impacts (although none of those advantages would essentially be obvious as a result of local weather system’s pure variability).
We should always point out that our 100 kilotons per yr situation is bigoted. We outline a subscale deployment to imply a deployment massive sufficient to considerably enhance the quantity of aerosol within the stratosphere whereas being effectively beneath the extent that’s required to delay warming by a decade. With that definition, such a deployment could possibly be a number of occasions bigger or smaller than our pattern situation.
In fact no quantity of photo voltaic geoengineering can remove the necessity to scale back the focus of greenhouse gases within the ambiance. At greatest, photo voltaic geoengineering is a complement to emissions cuts. However even the subscale deployment situation we take into account right here could be a big complement: over a decade, it might have roughly half the cooling impact as eliminating all emissions from the European Union.
The politics of subscale deployment
The subscale deployment we’ve outlined right here may serve a number of believable scientific and technological targets. It could display the storage, lofting, and dispersion applied sciences for larger-scale deployment. If mixed with an observational program, it might assess monitoring capabilities as effectively. It could straight make clear how sulfate is carried across the stratosphere and the way sulfate aerosols work together with the ozone layer. After a couple of years of such a subscale deployment, we might have a much better understanding of the scientific and technological limitations to large-scale deployment.
On the similar time, subscale deployment would pose dangers for the deployer. It may set off political instability and invite retribution from different international locations and worldwide our bodies that will not reply effectively to entities fidgeting with the planet’s thermostat with out international coordination and oversight. Opposition would possibly stem from a deep-rooted aversion to environmental modification or from extra pragmatic issues that large-scale deployment could be detrimental to some areas.
Deployers could be motivated by a variety of concerns. Most clearly, a state or coalition of states would possibly conclude that photo voltaic geoengineering may considerably scale back their local weather danger, and that such a subscale deployment would strike an efficient steadiness between the targets of pushing the world towards large-scale deployment and minimizing the chance of political backlash.