It could be very ugly.
http://scied.ucar.edu/shortcontent/mount-tambora-and-year-without-summer
“Mount Tambora and the Year Without a Summer”
The summer of 1816 was not like any summer people could remember. Snow fell in New England. Gloomy, cold rains fell throughout Europe. It was cold and stormy and dark - not at all like typical summer weather. Consequently, 1816 became known in Europe and North America as “The Year Without a Summer.”
Why was the summer of 1816 so different? Why was there so little warmth and sunshine in Europe and North America? The answer could be found on the other side of the planet - at Indonesia’s Mount Tambora.
On April 5, 1815, Mount Tambora, a volcano, started to rumble with activity. Over the following four months the volcano exploded - the largest volcanic explosion in recorded history. Many people close to the volcano lost their lives in the event. Mount Tambora ejected so much ash and aerosols into the atmosphere that the sky darkened and the Sun was blocked from view.
Sounds like the solution to global warming. /sarc