The plan sounds like science fiction — but could be fact within a decade; every day more than 800 giant aircraft would lift millions of tonnes of chalk dust to a height of 12 miles above the Earth’s surface and then sprinkle the lot high around the stratosphere.

In theory, the airborne dust would create a gigantic sunshade, reflecting some of the Sun’s rays and heat back into space, dimming those that get through and so protecting Earth from the worsening ravages of climate warming.

This is not the crackpot plan of a garden-shed inventor. The project is being funded by billionaire and Microsoft founder Bill Gates and pioneered by scientists at Harvard University.

This initial $3 million test, known as Stratospheric Controlled Perturbation Experiment (SCoPEx) would use a high-altitude scientific balloon (pictured) to raise around 2kg of calcium carbonate dust — the size of a bag of flour — into the atmosphere 12 miles above the desert of New Mexico

This initial $3 million test, known as Stratospheric Controlled Perturbation Experiment (SCoPEx) would use a high-altitude scientific balloon (pictured) to raise around 2kg of calcium carbonate dust — the size of a bag of flour — into the atmosphere 12 miles above the desert of New Mexico

Indeed, the plans are so well advanced that the initial ‘sky-clouding’ experiments were meant to have begun months ago.

This initial $3 million test, known as Stratospheric Controlled Perturbation Experiment (SCoPEx) would use a high-altitude scientific balloon to raise around 2kg of calcium carbonate dust — the size of a bag of flour — into the atmosphere 12 miles above the desert of New Mexico.

This would seed a tube-shaped area of sky half a mile long and 100 yards in diameter. For the ensuing 24 hours, the balloon would be steered by propellers back through this artificial cloud, its onboard sensors monitoring both the dust’s sun-reflecting abilities and its effects on the thin surrounding air.

SCoPEx is, however, on hold, amid fears that it could trigger a disastrous series of chain reactions, creating climate havoc in the form of serious droughts and hurricanes, and bring death to millions of people around the world.

One fear is that spreading dust (pictured) into the stratosphere may damage the ozone layer that protects us from hazardous ultraviolet radiation which can damage human DNA and cause cancers

One fear is that spreading dust (pictured) into the stratosphere may damage the ozone layer that protects us from hazardous ultraviolet radiation which can damage human DNA and cause cancers

One of the Harvard team’s directors, Lizzie Burns, admits: ‘Our idea is terrifying… But so is climate change.’ An advisory panel of independent experts is to assess all the possible risks associated with it.

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