Volcanoes erupt all the time, all over the world. However, the majority of these eruptions are from minor ones, hardly impacting the environment. The typical volcano sends sulphur dioxide into the troposphere, the atmospheric layer closest to the earth’s surface. The gas stays in the sky for a week before falling back to the ground as acid rain, just a few hundred miles from the volcano.
A large volcano however, shoots the sulphur dioxide into the stratosphere, which begins at seven miles above the earth’s surface. In that height, rather than falling back to the ground, the sulphur dioxide mingles with the stratospheric water vapour and forms a sulphur aerosol cloud. Aerosols are simply a combination of dispersed, fine and solid particles from different substances connected through water vapour. These sulphur aerosols can stay in the stratosphere for over a year and therefore have a significant impact on global climate.
This is exactly what happened after June 15th 1991, when Mount Pinatubo erupted in the Philippines. It injected more than 20 million tons of sulphur dioxide into the stratosphere, more than any eruption since Krakatoa in 1883. Following the eruption, the sulphur aerosol spread across the whole stratosphere through natural winds and covered the earth like a blanket. The result was a drop in the global temperature by 0.5°C in the years between 1991 and 1993 as this layer of sulphur dioxide increased what scientists call the planet’s albedo, or reflective power. The sulphur aerosol blanket reflected 1% of the sunlight coming towards the earth back into space and thus partially offset the warming effects caused by rising levels of greenhouse gases.
This phenomenon led many scientists to believe, that through controlled injections of sulphur dioxide into the stratosphere, global warming could be controlled and global temperatures could be reduced. A major advantage of this possibility is its cost effectiveness. According to calculations, 100 thousand tons of sulphur dioxide per year would effectively reverse warming in the arctic and reduce warming in the Northern Hemisphere. This number may seem a lot but is dwarfed when compared to the annual output of 250 million tons of sulphur dioxide ejected by volcanoes, motor vehicles and coal powered plants. So, the question researchers were asking themselves was essentially: How do we spray 128 litres of sulphur dioxide into the stratosphere every minute in order to stop global warming?
A group of scientists from the US that loves cheap and simple solutions proposed a very long hose for the cure. At a base station, sulphur would be burned into sulphur dioxide and then liquefied. The hose, which would only be a couple of centimetres in diameter would be about 18 miles long, reaching from the base station into the stratosphere. In order to keep the hose vertical, helium balloons would be attached to the hose. Additionally, small pumps would be attached to the hose in an 80-metre interval to elevate the sulphur dioxide to the top of the hose. At the end of the hose, the sulphur dioxide would be sprayed into the stratosphere, where natural wind patterns would disperse the aerosols over the globe.
This layer of aerosols would reduce the effects of global warming caused by greenhouse gases drastically. However, researchers and scientists agree, that using geoengineering does not mean that we should stop worrying about reducing our carbon dioxide emissions. The warming caused by atmospheric carbon dioxide build-up is practically irreversible, as climate change is directly correlated to the total cumulative emissions. So even if we were to immediately stop any carbon dioxide emissions, the elevated concentrations of the gas in the atmosphere will persist for decades and increase global warming.
Until now the method of injecting sulphuric aerosols in to the stratosphere seems too good to be true. And it is. Firstly, the ethical and governance issues of the proposed method are huge. Solving a problem, that only exists because of humans emitting gas into the atmosphere, by injecting a different gas into the atmosphere, doesn’t seem like a very good idea. Also, injecting sulphur into the stratosphere could have dangerous consequences such as disrupting precipitation patterns, whitening the sky or destroying the ozone layer.
The impact on ozone is probably the most worrisome outcome, as the ozone layer absorbs most of the Sun’s ultraviolet radiation and hinders it from reaching Earth’s surface. Ultraviolet radiation is very harmful to all living organisms as it can lead to genetic damages, skin diseases and immune system suppression. David Keith, a Harvard professor and a pioneer in geoengineering said that “the uncertainties are substantial. You could get very bad [ozone] outcomes, but there are also ways where you could have no impact, or even a positive impact, on ozone.” In any case, he says, it is “just crazy” not to begin conducting experiments on solar geoengineering to find out more.
Another idea worth considering is the “space sunshade”- a climate engineering method for mitigating global warming through solar radiation management. It is based on the idea that we would just need to divert 2-4% of the Sun’s rays, to take Earth back to its preindustrial climate. This would be achieved by placing trillions of tiny disks at the Sun-Earth Lagrange L1 point. This is a position in between the Sun and the Earth, where the gravitational pulls of both the bodies are in such a way that they balance out perfectly. This means that a small object, placed at the L1 point, could remain in that position without using too much fuel. The disks are proposed to have a 60cm diameter and a thickness of five micrometres and will weigh about a gram each. These disks would contain transparent lenses in order to deflect the light coming from the sun so it does not hit earth.
The estimated cost of this method, which is commonly referred to the “Venetian Space Blind”, runs at around $5 trillion, which could be spent on developing alternative energy. Another downside is that the construction time of the whole operation would be very long and replacing faulty disks could prove to be a severe challenge. Another difficulty, scientists assume is convincing governments and people that the cloud of disks could not be used as a weapon to change sunlight on various parts of the earth.
Of course, geoengineering methods have their downsides, however so do most of the options currently available for reducing or reversing global warming. David Keith stated that ”there is a realistic chance that solar geoengineering technologies could actually reduce climate risk significantly, and we would be negligent if we didn’t look at that. I’m not saying it will work, and I’m not saying we should do it.” But “it would be reckless not to begin serious research on it,” he adds. “The sooner we find out whether it works or not, the better.”