Blocking the sun is not a practical solution. Putting something up in the atmosphere is untested and super dangerous. It could cause all life on Earth to die out like the Matrix.

Physically blocking the sun is also practically impossible. It requires that we put an object in space in a Lagrange point (gravitationally stable points around Earth) which is very far away and the sun shield would have to be approximately the size of Brazil. Launching that much material into space and getting it into position, and then unfurling it would be a HUUUUUUGE undertaking the likes of which we have never seen. Plus, launching all those rockets, mining the materials, etc, would emit so many tonnes of green house gasses that by the time we actually did it we might be in an even worse position.