This is where people who think space access is only for satellites and LEO space stations have no imagination. We’re at a place now where if global warming did suddenly start to run away, within a year, we could realistically launch enough solar shades to meaningfully impact the situation. It’s far fetched, but this is why innovation in general is important. Not for what we know now, but for all the unknown ways it could be used in the future.

For those purposes, why would it need to be mirrors? We don't care to coherently reflect the light; we just want to block it.

(For reference, I think all of these are likely to be somewhere between moderately and incredibly bad ideas...)