Blocking the sun isn't any kind of a big idea. More than likely, all that talk by anybody who could do it is just fuel for the 'blab' fire they are trying to scare us with. If they wanted to bring on rapid world cooling, in an easy way, simply nuke two giant, dormant volcanoes into action, one in the Atlantic and one in the Pacific. Look up Krakatoa to see what the volcano result was back in the 1800s.