This is called Geoengineering, and we don't need volcanoes for that. Current approaches mostly consider injecting sulfates or other reflective aerosols directly into the atmosphere to influence how much solar radiation reaches the Earth. The principle is the same as behind volcanoes. This method is in fact already being employed and has been used in the past, albeit only for regional climate engineering.

Why don't we do this to stop climate change? As you yourself kinda noticed, the consequences could be very unpredictable and dangerous because the effects are difficult to model. However, maybe after everything else has failed Geoengineering could be a viable option.

Basically this:

geo engineering is a stopgap solution. it enables the continuation of fossil fuel burning, and rampant over consumption. it does nothing to prevent ecosystem collapse in our oceans, decline of breathable air or extinction of native species.

when you hear “geo engineering”, think of “clean coal” and “sustainable aviation fuel,” because they are one and the same

This guy thinks we can control volcanoes.

Watch Snowpiercer

Maybe take a bath next time!

Isn’t this what happened in the Matrix?

If you want to make a shade without choking life to death how about a big parasol in space? https://en.wikipedia.org/wiki/Space_sunshade