Most people probably will not have heard 1816 referred to as the Year Without a Summer, but that is exactly what the eruption of Mount Tambora in what is now Indonesia seems to have made it. That May, frost killed or ruined most of the summer crops. In June, two large snow storms produced substantial numbers of human casualties. Hungary and Italy got red snow, mixed with ash, while China experienced famine associated with sharply reduced rice production. In total, about 92,000 people died and the global mean temperature fell by 3°C.
One random yet positive consequence was constant rain causing Lord Byron to propose a writing contest, which Mary Shelley eventually won with Frankenstein. The increased cost of oats may also have driven a German man named Karl Drais to invent the first bicycle. (He called it the ‘velocipede,’ which sounds like a fast-moving and dangerous insect.)
Such incidents are inevitable on a planet that remains geologically active, but they certainly demonstrate the degree to which natural patterns can change rapidly, as well as the degree to which human beings are dependant upon them not doing so.