The experiment has already been done (by Mother Nature). In 1816 a volcano exploded in the south sea area and put so much ash in the air it blocked the sun for over a year. It was known as the year without summer.
Results were no crops and the temperature dropped. People died of starvation and of the cold! The experiment does not need to be repeated.
https://en.wikipedia.org/wiki/Year_Without_a_Summer
Never knew about that, thank you for posting.