(WHTM) — It was called the Year Without a Summer.

In 1816, the average global temperature dropped about one degree Fahrenheit. In the United States, there was snow in June across New England and New York. In July and August, lakes and rivers in northwestern Pennsylvania iced over. On Aug. 20 and 21, Virginia had frost. Many crops froze and withered in the fields, and because of constant cold rain, much of what could be harvested was so moldy it couldn’t be used for anything, even feeding animals.

It was the same all around the globe. In Europe, the crop failures triggered the continent’s worst famine of the 19th century and a series of typhus epidemics that killed thousands. China, too, suffered crop failures and famine. Disrupted monsoons in India caused three crop failures, famine, and cholera. And everywhere, people reported the same phenomenon — a reddish “dry fog” that dimmed the light from the sun, sometimes to the point where people could see sunspots with the naked eye.

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So what caused this worldwide catastrophe?

On April 5, 1815, in what was then called the Dutch East Indies and is now called Indonesia, the volcano Mount Tambora erupted. The eruption built up for several days until, on April 10, a massive explosion blew the top off the volcano, reducing its height from 14,100 feet to 9,354. An immense plume of ash — over 30 cubic miles worth — shot over 27 miles into the air. It’s the biggest volcanic eruption in recorded human history.

The cloud from the eruption stayed in the upper atmosphere and spread across the world. This included a great deal of Sulphur dioxide, which was the primary cause of the reddish “dry fog.” It not only dimmed the light from the sun but also reflected it back into space, so the energy of the sun couldn’t warm the Earth.

But while the Tambora eruption was the prime cause of the Year Without a Summer, it was not the only cause. In the years leading up to Tambora, a series of smaller volcanic eruptions pumped ash into the air: an 1808 eruption whose location has not yet been determined, La Soufrière on Saint Vincent in the Caribbean in 1812, Awu in the Sangihe Islands, Dutch East Indies in 1812, Suwanosejima in the Ryukyu Islands, Japan in 1813, and Mayon in the Philippines in 1814.

In addition, the “Little Ice Age” factored in. This was a period of cold weather lasting from the 16th to 19th centuries. Scientists believe the Tambora eruption aggravated the effects of this cooling.

The world was also experiencing the effects of the Dalton Minimum, a period of low sunspot activity which ran from the late 1700s to 1820. Minimums tend to correspond with global temperatures lower than average, though scientists are still trying to figure out why.

So many factors came together to make the Year Without a Summer happen, but there’s little doubt the Tambora eruption was the main trigger.

How many people died from the Tambora eruption? Estimates — and they really are estimates — are all over the place, depending on whether you count just those who died near the volcano or also those who died from the bad weather. Death tolls range from 10,000 to 90,000. We’ll probably never get an exact count since people at the time had other concerns.

By the way, Tambora is still an active volcano, though it’s unlikely to produce a similar explosion any time soon.

Information for this story was sourced from Wikipedia, University of Huston, Seasia.co, CNN, Smithsonian Magazine, History Daily, University Corporation for Atmospheric Research, USA Today, unbelievableinfo.com, University of Bern, The Old Farmer’s Almanac, The Washington Post, christopherroosen.com.