Stratospheric Aerosol Injection

What is it?

In 1991, Mount Pinatubo the Philippines erupted, throwing millions of tonnes of ash and sulphur into the upper atmosphere, cooling the earth by 0.4 degrees Celsius for close to a year. Stratospheric aerosol injection(SAI) hopes to simulate this phenomenon by injecting millions of tonnes of oversold( fine solid particles), which is normally sulphur, into the upper atmosphere (the stratosphere). This will block out enough of the sun's light and heat to artificially cool or stabilise the earth's temperature. This could be done relatively easily with technologies already available, and will probably use planes to deliver the aerosol, and could reduce temperatures in a matter of months.

Any problems?

One of the key concerns with SAI is the idea that it may benefit some areas, whilst having negative impacts on other areas. For example, many studies have shown that SAI would decrease rainfall, possibly causing droughts. However, these models do fail to consider that global warming itself will increase rainfall, so decreasing rainfall may keep rainfall at close to present day levels.

Many studies have indicates that cooling would be uneven, such as favouring the tropics over higher latitudes, and that SAI may cause increases in extreme weather. However, a recent study (Irvine et al. 2019) found that, in a very idealised model, water availability, extreme weather and temperature were reduced almost universally over all land, and in no where was warming exacerbated. However, it must be noted this is only one highly idealised study.

Many criticise the fact that SAI only masks warming, and doesn’t eliminate the threat. This means if, for any reason, it was stopped, then warming would be seen at a rate far faster than if it was never used in the first place. This would mean we would have to carry on implementing it until we reduce the amount of CO2 in the atmosphere to safe levels, which may be a long time.  Moreover, as it doesn’t address CO2, only warming, the acidification of oceans that cause coral reefs to be destroyed, and may destroy much more sea life, will continue.

Moreover, there are serious concerns about the impact of SAI and the ozone layer, and whether it may cause another hole in the ozone layer to form.

Many worry about the potential of SAI to cause a global conflict over who controls the ‘global thermostat. Worldward is working to try and create a safe governance system for SAI and other solar geoengineering techniques to avoid such a danger, but many may argue the danger will exist as long as the technology exists. Because of how cheap it can be implemented, some have theorised it could not only be implemented by one country by itself, but even by a few wealthy individuals.

Finally, many worry about the unforeseen side effects of SAI, and the fact that we may not be able to find these out until SAI is deployed. Moreover, as the aerosol takes months to fall from the upper atmosphere, it may not be able to be reversed for months if we notice something going wrong.

Potential Benefits

  • Could potential reverse up to half of global warming if we double CO2 levels

  • Could result in an increase in water availability and a decrease in extreme rainfall in almost every large region

  • May be extremely cheaply- possibly only about $2 billion a year to about $5 billion a year

  • The technology for SAI is far more developed than the technology for any other solar geoengineering solution, and SAI is best understood

  • This means that is Solar Geoengineering is needed to reverse catastrophic warming, SAI may be the best suited to work, no matter how imperfect and awful SAI is, we may have no choice but to implement it