A deep trough of low pressure spanned the Great Lakes. Behind it, a wall of cold air built and folded over itself, layer upon layer, until it was both towering and poised. Finally, it broke free to race east toward New England, where it would linger for 36 hours and create the most memorable weather event in the region’s history. Temperatures plunged more than 40˚. An American mistral howled from the northwest. Snow fell heavily, with hail added for variety. By the time it was done, the storm had extended west to Pittsburgh, Pennsylvania. Nobody, no matter how old, could recall any weather like it — in June.

And so it was that in June 1816, New England farmers stood in falling snow and watched ponds crust over with ice and buds on plants droop and then die. Hummingbirds, martins, and sparrows became “so benumbed, as to be taken by the hand, and great numbers… actually perished in the cold.”

People groped for an explanation. “Everybody seems to be at a loss to account for this strange weather,” noted one newspaper, “which…has got into a strange sort of a jumble.” That was an understatement. People would remember 1816 as “Eighteen Hundred and Starve to Death” because of the killing frosts that devastated crops in the crucial growing months of June, July, and August. People with a broader view would remember it as “the year without summer.”

Despite what anyone called it, everyone struggled to find a cause. Some argued that the growing accumulation of ice in the far North had become so large that the sun could no longer melt it. The chill of 1816 was for them a harbinger of a time when there would be “no summer at all,” a prelude to a rampage of nature that would leave man extinct in its wake.

The gullible were inclined to accept that conclusion. Doomsayers could point to the extraordinary amount of natural phenomena in recent years, especially in 1811 and 1812. The Ohio River had breached its banks to flood enormous parts of its valley wilderness. Plagues that put people in mind of biblical retribution felled pioneers across the frontier. The violent New Madrid earthquake caused the Mississippi River Valley to roll like an ocean. A large comet hung in the night sky, and an eclipse spooked the superstitious. “Many persons,” noted one observer in 1816, “suppose that the seasons have not thoroughly recovered from the shock they experienced at the time of the late total eclipse of the sun.”

Condescending scientists shook their heads over such nonsense. Blaming an eclipse for the wintry summer was the logic of the foolish amateur and the partially educated rube. No, they explained, “the peculiarities of the season [in] the present year” were the result of “spots on the sun.” They even had compelling evidence for the claim. In April 1816, a dark sport did indeed appear on the sun. Everyone could see it because of a thick haze that made viewing the sun safe with the naked eye. There, scientists assured everyone: Done and done; they had a consensus.

Of course, the consensus was as wrong about the year without summer as were eclipse advocates and doom-mongers, which isn’t surprising. Science is a bumbling art that stumbles on the truth more often than it proves a hypothesis. The scientific method cannot produce certainty. It can only eliminate the implausible. Cocksure science is junk freight, especially when it is the cargo of those both condescending and supremely confident.

And that makes the actual explanation for the weather that year ironic. It had nothing to do with the sunspots but had everything to do with the ability to see them. Nobody thought it strange that people could look at the sun with unprotected eyes. They noticed the sunspot, but they didn’t seem to notice the thick, persistent haze that allowed them to see the spot on the sun.

Yet having said that, concluding that the dense haze was causing the strange weather would have been only partly correct. The haze was simply another piece of evidence pointing to the real cause of Eighteen Hundred and Starve to Death. It was something that happened — or had happened — on the other side of the world.

Mount Tambora still dominates the landscape of Indonesia’s island of Sumbawa. Before 1815, though, it was an imposing promontory that rivaled anything in the Swiss Alps or Himalayan ranges in Nepal. Tambora, however, is a volcano, and in April 1815, it blew a good part of itself to smithereens with an eruption audible 2,000 miles away.

To put the event in perspective, volcanic eruptions are measured on a scale from 1 to 8. The Mount Vesuvius eruption in 99 AD that buried ancient Pompeii was a 5. The 1980 Mount St. Helens eruption in Washington State was also a 5. Krakatoa in 1883 was only a 6, but using “only” in this context does the event an injustice, for the scale’s gradations are geometric rather than linear. In other words, a 6 is much more intense than a 5. Krakatoa’s explosion struck the crews of distant sailing ships stone-cold deaf. Only four volcanic incidents in the last 2,000 years have been of a higher magnitude than Krakatoa.

Mount Tambora was one of them, coming in (or going out, as it were) at a whopping 7, which made it at least four times more intense than Krakatoa. It is the most violent volcano in recorded history. The April 1815 eruption turned the Indonesian day to night, devastated the region, set off lethal tsunamis, and filled surrounding waters with miles of floating pumice mistaken for seaweed by heedless mariners or for looming black icebergs by puzzled lookouts sweating in crow’s nests.

The pumice remained a menace to navigation for a decade, but the ash caused trouble worldwide. Tambora hurled an enormous quantity of ash skyward. The volcano threw solid and molten rock thousands of feet upward by some estimates, but it propelled ash upward forty miles or more. In the stratosphere, the ash spread first along the equator and then expanded as a cloud. It became an aerosol mist chemically transformed into particles of almost molecular miniaturization. In only a few months, the ash veiled the entire earth from Pole to Pole. Mount Tambora’s seismic cataclysm immediately altered the land and seascape for hundreds of miles around it. The more subtle atmospheric changes it caused were to alter people’s lives all over the world for years to come.

It did this by first tweaking temperatures and then radically altering established weather patterns. The aerosol cloud did not block sunlight as much as it reflected and distorted it. The optical effects were dazzling, especially in sunsets that Technicolor technicians would have rejected as too gaudy. Brilliant reds and purples during the summer and fall after Tambora’s eruption transfixed Londoners.

But Tambora’s ash was also in the process of transforming the tremendous weather-making apparatuses of the earth. The heaviest snow in memory fell that winter across Europe, lengthy storms that were made all the more peculiar (and alarming) by the strange coloring of red and yellow snowflakes. Drifts reached the eaves of houses and smothered livestock as if in an avalanche.

Yet, the strangest aspect of the winter of 1815-1816 was how Tambora’s ash made winter milder in North America while it was pasting Europe with weirdly colored snowfalls of abnormal intensities. Abstruse explanations of how atmospheric conditions and weather patterns interact can account for this, at least according to people who say they can predict as well as clarify the weather. Whatever the case, the aerosol ash interfered with the way the sun’s seasonal position warms cool regions and cools warm regions. In short, the ash turned everything either upside down or sideways, and the weather lost even a fraction of predictability.

The cloud affected more than sunlight; it dampened solar energy and caused continents and oceans to cool. The effect on polar air circulation temporarily blocked seasonally cold air in the upper United States, which was the reason for America’s mild winter in 1815-16. While the ash’s reflective properties cooled the lower atmosphere, they also impeded the seasonal flow of arctic air during the winter.

With the onset of spring in 1816, the cooling continued, and the arctic air did not do what it was supposed to. Rather than retreat, it advanced just as the seasonal shifting of the earth exposed the Northern Hemisphere to the sun’s energy. The return of solar energy to the Arctic rapidly dissipated the unique wind patterns that the ash cloud had produced. Liberated arctic air flowed south over Canada in one hemisphere and over Scandinavia in another to make springtime vaguely different for everybody. It would make summer memorably so.

Québec had a foot of snow in April, the product of a front marching south toward New York and the Ohio River Valley. Both places had early and heavy snowfalls, but warm weather returned by the end of the month. On the other hand, Western Europe had no spring and lost April and May to intense cold that descended and stayed. Meanwhile, New England was on a see-saw. As April had done, May brought brutal cold hurtling down from Canada, but it was late enough to find budding plants and fruit trees to freeze. As it had in April, the cold abated and was replaced by humidity and spring rains throughout New England. Farmers were hopeful.

The winter storm in June all but dashed their hopes, but hot weather returned at the end of the month. Then Fourth of July celebrations saw men in overcoats and women wrapped up and wearing mittens. In Canada, ponds froze, and on July 8, frost killed crops in New England while chilly weather stunted the fields of the mid-Atlantic. It also stopped raining (or snowing) because less heat meant less evaporation from land and water. Virginia buckled under a severe drought. In the second week of August, a killing frost burned the Yankee corn crop, the final blow to an already abbreviated growing season. Harvests did not happen that fall, and fodder was scarce and food scanty in the coming winter.

Faulty memories can exaggerate, and people often make the ordinary dramatic in recollection. But contemporary temperature measurements provide hard data to bear out the fantastic stories of old-timers recalling summer snow and killing frosts in August. Data suggests the ash cloud reflected enough sunlight to lower the average temperature in 1816 by some 3˚ Fahrenheit, and the running temperature on many days was often 5 to 7˚ lower than usual. Even that tells only part of the story. The steep drop of the thermometer during cold fronts and the “winter storm” of June started a calamitous agricultural crisis for the entire world. Grain prices quadrupled in Central Europe, and starving Asian peasants watched rice patties either dry up or skim with ice.

In America, hard-bitten Yankees and debt-ridden southern planters prayed for sunshine or rain or warmth on any given day, and occasionally all of those things within a span of hours. Their desperation was real. Seed corn from 1815 soon sold for $5 a bushel, almost $100 in today’s money.

Aerosol clouds from volcanic eruptions have a 3-5 year life span and are densest in their second to third year. They then gradually diminish. Mount Tambora’s ash did this, and by 1818 seasons returned to their routines of cold in winter and warmth in summer. As life settled back into traditional patterns of planting, nurturing, and harvesting, the Americans who had endured the year without summer reflected on 1816 with their characteristic humor. They dubbed it “Eighteen Hundred and Starve to Death,” while educated observers pinned the cause on sunspots.

It’s easy to look back at 1816 and chuckle over those poor scientists, comically ignorant and without a computer model to call their own, yammering about sunspots while overlooking the actual cause of the weather. We know so much more than they, we think, cocksure and confident.

Yet 1816 is something more than a year without summer. It is, in fact, a warning about something other than the climate. Cocksure consensus isn’t a thing isolated in the ignorant past, as Hamlet warned Horatio. As we remind ourselves that there are indeed more things in heaven and earth than we can know, we should look at 1816.

It is a mirror.