Bill Gates wants to spray millions of tonnes of chalk into the stratosphere to reflect sunlight and slow global warming

The first test of a project backed to spray millions of tonnes of chalk into the stratosphere, in an attempt to ‘dim the sun’ and cool the Earth, could happen in June.

Harvard University experts will test the system by sending a large balloon 12 miles above the Swedish town of Kiruna and have it drop 2kg of chalk dust into the stratosphere.

The aim of the estimated $3 million mission, backed by billionaire Bill Gates, is to have the chalk deflect a portion of the sun’s radiation, stop it from hitting the surface, and cool the planet.

The idea has been heavily criticised since its inception, with project director Frank Keutsch even calling the need for this scale of geo-engineering ‘terrifying’.

And experts have warned that the unusual technique could be disastrous for weather systems in ways nobody can predict.

Backed by a range of private donors including Gates, the test mission is launching from Sweden as they could offer a launch by the end of this summer. 

The test balloon will lift 600kg of scientific equipment 12 miles above the surface of the Arctic town and if it all goes well, about 2kg of dust will be released. 

This will then create a dust plume several kilometres in length – not large enough to have any effect on the intensity of the sun’s rays hitting the Earth. 

During that first test the team would gather information on how particles of dust react with the air. 

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