When Mount Pinatubo erupted in the Philippines in 1991, it spewed nearly 20 million tonnes of sulphur dioxide and ash so high into the atmosphere that it hung there for years, screening sunlight from reaching the Earth's surface.
As a result, the planet was about 0.5 deg C cooler until 1993.
That eruption has often been used by scientists as an analogue for geoengineering - an emerging field of science where deliberate changes to natural systems are made to help cool the planet.
In March, for instance, the National Academies of Sciences, Engineering, and Medicine in the United States urged the federal government to spend at least US$100 million (S$132 million) to conduct research on solar geoengineering strategies to reflect away some sunlight from reaching the planet's surface.
This can be done by injecting the stratosphere with certain aerosols like sulphur dioxide to increase the reflection of sunlight back into space - mimicking the effects of the volcanic eruption of 1991.
Particles in the stratosphere, which is higher than the clouds, take longer to dissipate to be "washed away" by rain. Clouds are in the troposphere - the layer of the atmosphere that ends at about 11km from the Earth's surface.
While the 0.5 deg C cooling caused by the Pinatubo eruption may not sound like much, such temperature changes are significant for the earth system.
Countries are now working to limit planetary warming to 1.5 deg C above pre-industrial levels, a threshold that scientists say if breached could have catastrophic consequences for lives and livelihoods worldwide - certain extreme weather events could get more intense, sea levels will rise faster and weather patterns get more erratic.
But solar geoengineering is also mired in controversy.
Scientists say geoengineering could detract attention from efforts to cut greenhouse gas emissions in the first place.
Others cite uncertainties in how the earth system will react to the introduction of yet another man-made substance into the air.
Volcanologist Fidel Costa from the Earth Observatory of Singapore at Nanyang Technological University said: "The main challenge is that the temperature effects from massive eruptions are temporary.
"So this means that we would have to continuously pump particles and dust to the atmosphere to keep the temperature down.
"There are a lot of ethical and political issues as well."
The New York Times reported that if solar geoengineering changes rain patterns, farming nations could suffer.
Associate Professor Benoit Taisne from the same institute added: "To geoengineer, you need factories to produce sulphur and aerosol particles. What are the environmental impacts of that?"
Shabana Begum
