Older volcanic rocks tend to emit less infrared, say the researchers, because carbon dioxide and sulphur dioxide in the planet's atmosphere weather the rocks and change their composition.
The researchers are also working with the regulator in Maharashtra, a neighbouring state, to introduce a market for sulphur dioxide, another pollutant.
For years, its power stations had been emitting large amounts of sulphur dioxide, which was falling back to Earth as acid rain, causing harm to plants, aquatic animals and infrastructure.
The idea is to inject sulphur dioxide—or perhaps other chemicals such as calcium carbonate or powders made of aluminium or diamonds—not into the troposphere, but the stratosphere, which begins up to 20km above the surface.
This would involve using sulphur or hydrogen sulphide aerosols so that sulphur dioxide would form clouds, which would, in turn, lead to a global dimming.
Sulphur dioxide is particularly influential because of how it combines with water to form sulphuric aerosols—a light-scattering haze which hangs in the sky.