On 10 April 1815, on the Indonesian island of Sumbawa, Mount Tambora exploded in the largest volcanic eruption in modern history. The force of the blast created a plume of aerosol sulfates, covering roughly nine million square kilometers, that reached the stratosphere and cooled temperatures in the northern hemisphere by approximately three degrees Centigrade for three years. In his recent study, Tambora: The Eruption that Changed the World, Gillen D’Arcy Wood documents Tambora's far-ranging effects in Switzerland, North America, Ireland, India and Yunnan Province in China: unseasonable cold, anomalous precipitation patterns, crop failures, famine, and millions of deaths worldwide from starvation and disease. As Wood demonstrates, Tambora created a worldwide climatological catastrophe that paradoxically went nearly unrecognized at the time; there were only a handful of first-hand reports about the eruption from British ships in the vicinity of the island, and only one eyewitness account by the Raja of Sanngar, whose kingdom on Sumbawa was buried under meters of pyroclastic lava flows and ash. Across the northern hemisphere, from Thomas Jefferson's estate in Virginia to the Swiss Alps, where Byron and the Shelleys spent a wet, cold, and miserable summer in 1816, commentators grimly noted devastatingly unseasonable cold, crop failures, and the impoverishment of peasants and small farmers who found themselves starving, even as grain prices soared. Yet without eyewitness reports of the eruption and without a modern scientific understanding of volcanology, writers across Eurasia and North America interpreted the Year without a Summer in moral terms: the cascading effects of Tambora were seen, at once, as political failures of regimes in power; as proof of the moral and socioeconomic corruption of entire societies; and as evidence of divine or heavenly retribution. Tambora emerged as a climatological phenomenon only with the development in the late twentieth century of tree ring and ice core analyses and sophisticated computer modeling. Therefore, as Wood suggests, the significance of this massive eruption for nineteenthcentury global history – and for our understanding of ‘future impacts of multidecadal climate change’ – only recently has begun to reshape how scientists and now humanists can study the wide-ranging ecological effects of the Year without a Summer.