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Head to shopify.com/scishow to learn more and for a 14-day free trial. [♪ INTRO] For as long as people have existed on this planet, volcanoes have been a kind of wildcard that could change the course of human history with a single explosion. Mount Vesuvius is probably the most famous example of this: It wiped out Pompeii and most of its inhabitants within minutes in 79 CE.

In 1600 BCE, the eruption that created the famous caldera on the Greek island of Santorini is thought to have destroyed the Minoan civilization. But not all volcanoes change history so quickly or dramatically. For decades, scientists have been exploring how volcanic eruptions can alter the climate across the whole planet for months, or even years.

Research suggests that these climate changes had major effects on the societies that experienced them, leading to things like famine, violence, and societal unrest. While these brief periods of climate change are different from the long-term and human-caused climate change that’s going on today, they can still give us insight into how human populations react to sudden environmental change. And maybe that can help us predict how modern society might react to the climate crisis that’s happening now.

Volcanoes are famous for the destruction they cause in their immediate surroundings. But their effects can reach way further. Volcanic eruptions fill the air with ash, which blocks sunlight and creates a cooling effect that can stretch around the globe if the eruption is big enough.

And just like global warming, this global cooling can have all sorts of consequences for ecosystems, weather systems, and the people who depend on them. . For instance, the land cools faster than water, so global cooling can reduce the temperature difference between the land and the sea. In parts of Asia, that can weaken monsoon rains.

Less rainfall can lead to drought and smaller crop yields, which can in turn lead to famines. And at that point, societal unrest often isn’t far away. And there are clear connections between environmental stress and societal unrest, both in the present and the past.

And knowing this led some scientists to wonder how major volcanic eruptions could be connected with historical events. One 2017 study on Ancient Egypt explored this question by comparing the timing of eruptions to the water levels in the Nile. The authors found that major volcanic eruptions all over the globe were linked with lower water levels in the Nile.

Flooding seems to have regularly decreased following eruptions. Less flooding would have been bad for crops, which depended on floods to bring in water and nutrients every year. But that may not have been the only consequence.

The team took their analysis one step further and studied Ancient Egyptian documents that held information about, like, what was going on in society at the time. They concluded that the environmental stresses caused by the reduced water levels following volcanoes may have led to riots during the time of Cleopatra. In other words, according to their findings, social unrest may have been directly related to faraway volcanoes that they would not have even known about.

Now, not all scientists were totally convinced that the social unrest in Ancient Egypt could be tied back to volcanoes, but this idea was intriguing. And in a 2022 study, one team of researchers from China conducted a similar study, focusing on the effect of volcanoes on Chinese history. Specifically, they wanted to answer the question of whether or not volcanic eruptions systematically topple governments.

To answer this question, they looked at a broad swathe of Chinese history, covering most of the last two millennia. Their first task was to find out around what year each Chinese dynasty fell. Fortunately, Chinese historical records are incredibly comprehensive.

China is an old society, and record keepers took note of everything: historical events, weather, climate, and even astronomical phenomena, going back at least 3500 years. So the researchers were able to pin down the approximate date that each dynasty ended. But figuring out the timing of nearby volcanic eruptions was a little more complicated.

For this part, they turned to evidence that was preserved in layers of ice in Greenland and Antarctica. See, after volcanoes throw a bunch of ash into the air, it eventually settles back down to Earth. In most of the world, that ash mixes back in with the soil and disappears.

But in places where the ground is covered in ice, that ash doesn’t go away. It stays in the ice, and over time, new layers of ice cover up the older ones. So, today, scientists can drill into the ice and extract a long cylinder, known as an ice core, which contains all these layers going way back in time.

By looking at the amount of ash in different layers, researchers can figure out approximately when significant volcanic eruptions took place. They can sometimes even figure out which volcano erupted. That’s because each volcano has a different chemical signature, depending on what kinds of materials it spews into the air, and this can serve as a kind of volcanic fingerprint.

So, the authors of this study examined a set of ice cores and searched and searched for eruptions that happened in the Northern Hemisphere between year 1 CE and 1915, a few years after the fall of China’s last dynasty and they found 158. Generally speaking, when they compared these eruption dates to Chinese historical records, they found that eruptions in the Northern Hemisphere tended to be followed by hard times in China. Chinese society often faced issues such as severe drought, flood, frost, and even outbreaks of plagues and locusts happening shortly after an eruption event.

Eruptions were also marked by less rain during the monsoon season, which is essential to Chinese agriculture. Out of all the eruptions they identified, the researchers then looked for any that happened up to ten years before or two years after the official date of a dynastic collapse. And they chose this window because the dates in historical records are only approximations, so there’s some uncertainty of up to two years on some of them.

And they looked at the whole 10 years before a collapse because not all regimes fall quickly, right? Sometimes, hard times don’t immediately topple a regime, but can lead to years of civil unrest before the government cedes power. Within these windows, they found something remarkable.

They observed that 62 out of 68 dynastic collapses were accompanied by an eruption event in the same window of time. In other words, they found that more than nine out of 10 of all Chinese dynasties’ fall was associated with a volcanic eruption. In some cases, they were even able to connect specific eruptions to a dynasty’s collapse.

For example, the 1641 eruption of Mount Parker in the Philippines was followed closely by the collapse of the Ming dynasty in 1644. Now, previous researchers had picked up on the fact that certain dynasties had collapsed during tough environmental times. Both the Tang dynasty and the Yuan dynasty collapsed during periods of cold and drought.

But prior to this 2022 study, the idea that climate change and extreme weather could play a role in the fall of governments was pretty controversial because there just wasn’t a lot of hard evidence. What sets this study apart is that it wasn’t just looking at one or two events in history. It was the first to really look at the effect of climate on history, on a large scale.

It included enough examples that the authors could use statistics to estimate the probability of these events aligning by chance. And they found that there was only a 1% chance their results could have come up randomly. So, this study offers the strongest evidence yet that there is a significant link between volcanic activity and human society.

But there’s one curious detail in all this. And that is that not every eruption on the record was linked to social unrest or a dynastic collapse. In 1815, Mount Tambora erupted in Indonesia.

This eruption was the strongest recorded in human history. It cooled the summer across the Northern Hemisphere by half a degree Celsius, and in Europe, 1815 became known as “the year without a summer.” Despite well recorded climate changes all over the Northern Hemisphere, this disruptive event did not cause any social upheavals in Chinese history. Researchers believe that this is because Chinese society was stable in 1815.

When Mount Tambora erupted, there was no large-scale warfare or social unrest. So, the researchers suspect that the Chinese people were able to weather the hard times without any regime change. If this interpretation is right, the researchers’ finding suggests that climate change doesn’t have to cause social unrest.

Like, if the extreme weather happens in a place that’s stable, with support systems or food reserves in place, environmental stressors might not disrupt society too much. And even though this study was all about events that happened in the past, it may have some interesting insights for us now that we’re in an era of global climate change, with more changes on the way. Because climate change is already disrupting societies by causing problems like droughts and food shortages, especially in the Global South.

But by investing in systems that make vulnerable societies strong and resilient, we may have a better chance at making it through challenges like these. In the past two centuries, there have been relatively few destructive volcanic eruptions. But, as advanced as societies have become, there is no escaping the fact that climate and society are intertwined.

In fact, sometime around the end of 2022 or in 2023, scientists are expecting to see a dip in temperatures caused by the massive explosion of the Tonga volcano in January of 2022. This won’t make a dent in human-caused climate change in the long term, but it will still be a measurable effect. The thing is, whether or not environmental stress is caused by volcanoes, it can wreak havoc on human society.

And as the planet warms, every part of the globe is going to experience certain environmental stresses. While most of the planet will rise in temperature rather than fall, these changes will likely be similar to the ones caused by volcanic eruptions. The difference is, while volcanoes only affect the climate for a couple of years, the crisis of anthropogenic climate change will create longer-term disturbances.

But now that we have research to give us an idea how these changes may affect society, we’re in a better position than anyone else in history to prepare ourselves for the changes that are coming. So clearly, our world can be more connected to itself than we thought and sometimes, when you run your own business, people on the other side of the world might benefit from your product. And Shopify can help you show the world how awesome your business really is.

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And also thanks to all those emperors out there who everybody thought it was there fault but it turns out just some volcano half way across the world really messed things up for them. [♪ OUTRO]