A volcanic eruption in 1815 proved even small changes in climate have disastrous global results

This is not the first time in recent history that humanity has had to deal with a dramatic shift in the climate. To get a glimpse of the political and economic effects climate change might bring, we don’t need climate-modeling systems to look to the future—we need to go back 200 years in the past.

Donald Trump’s ascent to the US presidency brings with it a renewed string of flagrant instances of global-warming denialism. But science has already spoken: A difference of just a few degrees in average global temperatures is associated with a number of far-reaching effects, such as food shortages, political unrest, mass migration, and a more rapid spread of diseases.

How do we know? Well, that’s what happened last time.

In 1815, an Indonesian volcano called Tambora erupted, sending an astronomically sized ash cloud into the air. What followed was a dizzying series of catastrophes—from worldwide famine to the spread of cholera, the world’s first pandemic—that paint an all-too-graphic picture of what we can expect in future if we don’t slow the progress of climate change today.

The biggest eruption in human history

When Tambora erupted in April of 1815, the blast was so loud it could be heard 1,200 miles away. It sent 12 cubic miles of rock hurtling into the stratosphere, halving the size of the mountain and creating an ash cloud the size of Egypt. The sulphur dioxide (SO2) released by the explosion was then distributed around the world by high-altitude winds, blocking some sunlight, and eventually cooling the earth’s atmosphere. “On average it was eight degrees colder in July than usual,” says Wolfgang Behringer, a history professor of the early modern period at Saarland University, and the author of the book Tambora and the Year Without Summer.

As Behringer’s title suggests, the following year, 1816, was known as “The Year Without a Summer.” It was characterized by heavy rains, cold weather, and snow falling in the middle of summer throughout northern climes. During these frigid months, the US recorded its only instance of zero tree growth according to absent tree rings. But there were even larger problems than stunted trees.

The social backlash

First came crop failure and famine. So many people were made destitute in France that visiting tourists mistook beggars for marching armies. Ruprecht Zollikofer, a Swiss journalist writing about the famine, described the scene (link in German) in 1817 as follows: “If a businessman walks through the streets, he’ll be pursued by swathes of the pitiful ones. When he approaches his lodging, it appears as if he were being pushed along the streets by a gust of wind as hundreds of them surround him.”

As people became more desperate, crime levels increased. In London, conviction rates almost quadrupled in the course of just two years. Similarly, continental European mortality rates in 1817 went up by 50% compared with the already-elevated rates of 1815, which was the end of the Napoleonic wars.

Economic and political turmoil

According to John Post, an economic historian of the Tambora period, the upheaval would eventually inspire an authoritarian streak that marked the political landscape of post-Napoleonic Europe. Fear of agricultural shortfalls also led to some governments adopting protectionist policies; it was during this time that tariffs and trade barriers first began to emerge as standard elements of the transatlantic trade system.

In Scotland, Wales, and England, the army had to be called in to quash demonstrations. Governments that couldn’t maintain control, as was the case in China, were severely weakened. In his book, Behringer even goes so far as to argue that China’s relative inability to manage disruptions in 1817 became one of the main contributing factors to its decline as a world power in the 19th century.

Mass migration and the emergence of new diseases

In the face of social upheaval, many in Europe opted to seek refuge in North America, setting off one of the biggest migratory surges in history. But arrivals in New England found that excessive rain had decimated the crops there, too. The situation became so dire that villagers in Vermont are reported to have lived off of a diet of porcupines and boiled nettles.

Beyond the political, economic, and social consequences, the aftershocks of Tambora could be observed in the sphere of healthcare as well: The sulphate-dust layer that the volcano spewed disrupted monsoons in south Asia for three years in a row. These conditions in turn gave rise to the Bengali cholera epidemic, which spread across the entire world, becoming the first global cholera pandemic and killing millions.

What can we learn

Granted, there are significant differences between the Tambora eruption and present-day climate change that make a direct comparison difficult. For one, the Tambora changes were sudden and unexpected, whereas present-day climate change has been relatively gradual. Secondly, the globalized economy is more diversified and interconnected today than it was in the 1800s. And thirdly, the aerosols emitted by Tambora led to net cooling of the planet, not a warming.

Given that we have a number of models that track and predict the rate of climate change, we should be better able to plan for and adapt this time around. However, we must remember that the effects will not be felt uniformly: Some regions will get more snow, others will see less rain; some places will have wetter winters and others drier summers.

The interconnections in the global economy should also allow us to offset local shortages through trade this time around, but Rüdiger Glaser, a geographer who studies the history of climatic developments, cautions that these kinds of advantages don’t offer any real solace. “We are more resilient in one way,” Glaser explains, referring to the opportunities presented by trade, “but we are still vulnerable in other ways that we may be unaware of.”

Glaser goes on to argue that no matter how advanced our economies become, there is no escaping our fundamental dependencies. “Our basic needs are food and health,” he says. Once food security is threatened, we all become vulnerable to the knock-on effects observed in the Tambora crisis—including political upheaval and, ultimately, mass migration in the form of economic refugees.

Take the Arab Spring, for example: A heat wave in Russia, Canada, and other leading wheat-producing countries became one of the triggers for an increase in bread prices. This was felt particularly acutely in the Arab world, which is a net importer of wheat. When the Syrian, Egyptian, and Tunisian governments failed to ameliorate these effects, instability followed. The consequences of the resultant unrest, at least in the Syrian case, are still being felt all around the world today, demonstrating how a climate-related event can have drastic follow-on effects in other sociopolitical realms.

Most disturbingly, unlike the effects of Tambora eruption, which disappeared after about two years, modern-day climate change has no end in sight. This time the aerosols will not dissipate, nor will there be a reversion to previous temperatures or precipitation levels once the world finds its way back to equilibrium. In that regard, the aftermath of Tambora should not just be seen as a cautionary tale, but as a sobering prologue.

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