Why blocking the sun to cool the planet is bound to go wrong

An Israeli company called Stardust Solutions revealed details last week about their plan to cool the planet by blotting out the sun using microscopic particles — a plan they intend to sell to governments. Solar Engineering, as it is called, and the broader idea to technologically modulate global temperatures, have been around for a long time. For most of that time these ideas have not been taken very seriously by those calling the shots.

But in recent years climate interventions have been slowly making their way into the mainstream as greenhouse gas emissions and global temperatures continue to rise. In a way, it is an attractive idea. Spraying tiny particles 16km into the atmosphere by specially-designed high-altitude aeroplanes to reflect sunlight back into space can be done at relatively low cost (around €10bn a year). No large-scale tests have ever been carried out, but we know it is possible. In 1991, the Pinatubo volcano erupted , blasting vast amounts of sulphuric acid into the upper atmosphere. A year later, global temperatures were 0.7 degrees Celsius below average. The Pinatubo volcano erupts, 12 June 1991 – here seen from over 40km away (Pic: Wikimedia ) Stardust Solutions, the world’s first major geoengineering start-up, has raised $75m (€64m) in commercial funding and proposes to mimic this effect using amorphous silica, used in toothpaste and other consumer goods, and calcium carbonate, a compound found in chalk, at an expected annual cost of $1.5bn. The privately-owned company laid out its stall last week in six yet-to-be peer-reviewed academic papers, and substantial media coverage followed, including from the New York Times and Politico. The latter described it as a “closely-guarded plan,” that required scientists to sign nondisclosure agreements. The company intends to patent the particle. Since none of the research has been independently reviewed, there is no way to confirm that any of it is actually new. And there are good reasons for scepticism: research into solid aerosols, their reflective properties, and the risks of ozone depletion is over a decade old.

Key points

• But in recent years climate interventions have been slowly making their way into the mainstream as greenhouse gas emissions and global temperatures continue to rise.
• In a way, it is an attractive idea.
• Spraying tiny particles 16km into the atmosphere by specially-designed high-altitude aeroplanes to reflect sunlight back into space can be done at relatively low cost (around €10bn a year).
• No large-scale tests have ever been carried out, but we know it is possible.
• In 1991, the Pinatubo volcano erupted , blasting vast amounts of sulphuric acid into the upper atmosphere.