We’re trained to love summer. From the moment you start school, the year splits neatly into term time and those long empty months, and even after you’re grown and stuck in an office, summer still means barbecues, beaches, and being outside.Losing a few weekends to rain is annoying. Losing the entire season is something else.Because that happened. Two hundred years ago the world went through a stretch history now calls the year without a summer.In 1815, Mount Tambora in Indonesia erupted.Volcanic eruptions get measured on something called the Volcanic Explosivity Index, which works a bit like the Richter scale does for earthquakes, tracking explosivity, the volume of ash thrown out, and how high that ash climbs into the atmosphere.For comparison, Mount St. Helens and Vesuvius both rated a 5. Tambora rated a 7, making it the largest volcanic eruption in recorded history.It threw 160 cubic kilometers of material into the atmosphere, and the explosion was reportedly heard 2600 km away.Over 10,000 people died immediately, with the total death toll estimated above 70,000. Those numbers only cover the eruption itself, though. What came afterward reached considerably further.What Can a Little Volcano DoChaos theory has that famous image of the butterfly effect, where a butterfly flapping its wings sets off a chain of events ending in a hurricane on the other side of the planet.Now make the butterfly a volcano.Close to Tambora, plant life simply burned. Further out, crops disappeared under ash, which was found as far as 1300 km away, wrecking harvests across Indonesia.The eruption was powerful enough to disrupt the monsoon season, which agriculture across southeast Asia depends on entirely. Torrential rain arrived late, cold snaps hit in between, and crops failed across the region.Then came the part nobody expected. The combination of strange weather and famine created ideal conditions for cholera, and the disease spread from the Bay of Bengal and the Ganges all the way to Moscow.Hold that thought, because cholera isn’t finished with this story.Moving west, ash in the atmosphere produced brown snow in Hungary and red snow in Italy. Cool temperatures and heavy rain swept across Europe, and the crops failed there too.Yields collapsed in Germany, Britain, and Ireland. Switzerland declared a state of emergency over famine. Together it became the worst famine Europe experienced in the entire 19th century.And cholera followed the trade routes, arriving on merchant ships and killing many more.North America didn’t escape either. 1816 wasn’t the coldest year on record, but the frosts and cold snaps landed at the worst possible time, right through the growing season.New England took heavy frosts on June 7 and 8. Philadelphia saw snow drifts of 45 to 51 cm, and parts of Canada got over 60 cm. Frost kept returning through July and August, alternating with sudden swings back to normal summer heat.Some farmers managed to harvest something. Between reduced production and the difficulty of moving food in that weather, prices went vertical anyway.A bushel of oats cost the equivalent of $1.57 in 1815. The same bushel cost $12.98 in 1816.Farmers in the region started calling that year eighteen hundred and starve to death. In some areas the disruption lasted until 1818, and the Germans named 1817 the Year of the Beggar.The Strange Things That Came Out of ItHistory is messier than it looks, and people are unexpectedly resilient. So while a volcano was blocking the sun, a few remarkable things happened anyway.Medicine took a step forward. The cholera epidemics Tambora helped trigger killed enormous numbers of people, but in London they also prompted serious debate about how disease actually works, laying groundwork that John Snow later used to figure out how cholera spreads. It remains a threat today, though we fight it far better because of research that began back then.We also got Frankenstein. The famous writing contest between Mary Shelley, Percy Shelley, and Lord Byron happened precisely because the weather was so miserable that the three of them were stuck indoors looking for something to do.Even the bicycle traces back to it. Failed harvests drove food prices up, which made keeping horses expensive, which pushed people to look for other ways to get around. Baron Karl Drais of Mannheim built the Laufmaschine, known in French as the Draisine, and that machine was the ancestor of the bicycle.Arctic exploration got a push too. Earth’s climate runs on interconnected wind and water currents, so when one region cools others can warm, and Tambora contributed to warming in the Arctic that encouraged expeditions searching for the Northwest Passage.The Part Worth RememberingClimate gets argued about endlessly in politics, considerably less so among scientists. What Tambora demonstrates is how fast these systems can shift.Every bit of the misery of 1816, the famines, the epidemics, the snow in June, followed an average temperature drop of somewhere between 0.4 and 0.7 degrees Celsius.Less than one degree. And we’re still talking about it two centuries later.