Which 1815 volcanic eruption caused the Year Without a Summer?

Tambora, in Indonesia - the largest eruption in recorded history, an order of magnitude bigger than Krakatoa. It removed about 1,400 metres from the height of the mountain, killed perhaps 70,000 people directly and by the famine that followed, and put enough sulphur into the stratosphere to cool the entire planet.

1816 is the year without a summer. Snow fell in New England in June, crops failed across Europe and North America, food prices spiked, and there was famine in Switzerland and unrest across several countries. It was also the wet summer that kept Byron's party indoors at Lake Geneva, where a ghost-story competition produced Frankenstein and the fragment that became the modern vampire.

Its other consequences are more surprising. The failure of oat harvests and the cost of feeding horses is one proposed spur for Karl Drais to build the first two-wheeled human-powered vehicle in 1817 - so the bicycle may descend from a volcano. Turner's unusually vivid sunsets in the following years have been attributed to the same aerosols, and the whole episode is now the standard historical case study when anyone models what deliberately putting sulphur into the stratosphere would do.