A sunshade seems like a horrible idea. There are obvious implications from the increased motivation to use fossil fuels. Biodiversity will continue to plummet until there is an ecological collapse. The people with the keys to enable or disable the shade will be influenced by short term profit. Then once fossil fuels are gone there will be a giant energy crisis. Buying time is good only if that time is properly paid for. And there is the risk of unintended consequences.
https://en.wikipedia.org/wiki/Unintended_consequences