Stratospheric aerosol injection (SAI) is an affordable and technically simple method of geoengineering. Using a balloons or drones lifting a hose into the stratosphere or modifying the fuel used in commercial planes would generate changes in the climate similar to a volcano. Volcano’s cool the climate over several years.
This approach is technically simple and 100 times cheaper than most other recommendations and provide several more decades for the switch from fossil fuels to be globally implemented. The fact that this simple approach exists along with other methods like using ten percent of the ocean for the growth seaweed means that climate doomsday is not going to happen. Technological interventions will be used. We should still get off fossil fuels but demands that the developing world stay poor (which costs millions of lives per year) or that everyone should upend their lives or that we should wreck the global economy to get to climate purity are stupid plans.
More detailed climate studies show that not only will surface temperature be reduced with stratospheric aerosol injection (SAI) geoengineering but if performed globally can also reduce tropical cyclones. However, large scale stratospheric aerosol injection in just one hemisphere would cause draught and other issues in the other hemisphere.
Delivery of precursor sulfide gases such as sulfuric acid, hydrogen sulfide (H2S) or sulfur dioxide (SO2) by artillery, aircraftand balloons has been proposed. It presently appears that this proposed method could counter most climatic changes, take effect rapidly, have very low direct implementation costs, and be reversible in its direct climatic effects.
One study calculated the impact of injecting sulfate particles, or aerosols, every one to four years into the stratosphere in amounts equal to those lofted by the volcanic eruption of Mount Pinatubo in 1991, but did not address the many technical and political challenges involved in potential solar radiation management efforts. If found to be economically, environmentally and technologically viable, such injections could provide a “grace period” of up to 20 years before major cutbacks in greenhouse gas emissions would be required, the study concludes.
According to estimates, one kilogram of well placed sulfur in the stratosphere would roughly offset the warming effect of several hundred thousand kilograms of carbon dioxide.
There are other more detailed geoengineering models that are now able to calculate how much sulfur dioxide is needed and roughly where it should be applied to achieve the desired temperature cooling.
The arguments in favor of this approach in comparison to other possible means of solar radiation management are:
Mimics a natural process: Stratospheric sulfur aerosols are created by existing natural processes (especially volcanoes), whose impacts have been studied via observations. This contrasts with other, more speculative solar radiation management techniques which do not have natural analogs (e.g., space sunshade).
Technological feasibility: In contrast to other proposed solar radiation management techniques, such as marine cloud brightening and space sunshades, much of the required technology is pre-existing: chemical manufacturing, artillery shells, high-altitude aircraft, weather balloons, etc.
Cost is 100 times less than climate change impact and most other recommended mitigation: The low-tech nature of this approach has led commentators to suggest it would cost less than many other interventions. Costs cannot be derived in a wholly objective fashion, as pricing can only be roughly estimated at an early stage. However, many sources suggest that it would be cheap relative to cutting emissions. The annual cost of delivering 5 million tons of an albedo enhancing aerosol to an altitude of 20 to 30 km is estimated at 2 to 8 billion USD. Around 5 million tons of SO2 delivered annually is predicted to sufficiently offset the expected warming over the next century. SO2 can be purchased online for as little as 500 USD per ton. In comparison, the annual cost estimates for climate damage or emission mitigation range from 200 billion USD to 2 trillion USD.
It would work: Most proposed solar radiation management techniques can only provide a limited intervention in the climate—one cannot reduce the temperature by more than a certain amount with each technique. New research by Lenton and Vaughan suggests that this technique may have a high radiative ‘forcing potential’.
Various techniques have been proposed for delivering the aerosol precursor gases (H2S and SO2). The required altitude to enter the stratosphere is the height of the tropopause, which varies from 11 kilometers (6.8 mi/36,000 ft) at the poles to 17 kilometers (11 mi/58,000 ft) at the equator.
Airliners could use lower-quality sulfur-rich fuels on higher altitudes. That approach would utilize regular flights and enable airlines to use cheaper fuels on long-distance flights. It would require using separate fuel tanks for takeoff and landing in populated areas, due to toxicity and olfactory sensations of sulfur oxides. This can be achieved in many airliners without difficulty, since they already have separate and selectable wing and fuselage fuel tanks.
Civilian aircraft including the Boeing 747-400 and Gulfstream G550/650, C-37A could be modified at relatively low cost to deliver sufficient amounts of required material.
Military aircraft such as the F15-C variant of the F-15 Eagle have the necessary flight ceiling, but limited payload. Military tanker aircraft such as the KC-135 Stratotanker and KC-10 Extender also have the necessary ceiling and have greater payload capacity
Modified artillery might have the necessary capability, but requires a polluting and expensive gunpowder charge to loft the payload. Railgun artillery could be a non-polluting alternative.
High-altitude balloons can be used to lift precursor gases, in tanks, bladders or in the balloons’ envelope. Balloons can also be used to lift pipes and hoses, but no moored balloon has ever been deployed to the necessary altitude.