In pictures: Global sunshade

Each glass flyer weighs only one gram - the same as a large butterfly.

On each would be a computer, a small camera to align itself accurately between the Sun and the Earth, and solar sails to guide it.

They would be receiving signals and doing two jobs: the first, to hold themselves perpendicular to the Sun so they cause the maximum shadowing, and second, not to move very fast so they do not hit their fellow flyers.