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In which John gets curious about the last time global human population declined and ends up learning about a period of human history called The General Crisis.
Thanks to Our World in Data for being such an amazing source of information about life on Earth: And thanks to Hannah Ritchie for answering my question!

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Good morning Hank, it's Tuesday.

I recently became intensely interested in a question. 'What was the most recent year in which the overall global population of humans declined?' I don't even remember why I was initially curious about this but I was, and I couldn't figure it out despite some pretty deep Googling and a visit to the library, so eventually I asked Max Roser who works at my favorite website, Our World in Data, but he didn't know either. One of his colleagues however, Hannah Richie, did find an answer. 

The last time the global human population decreased year over year was 1648, and the story of 1648 turns out to be really interesting and also like, uh, relevant. Ok, so the global human population actually decreased every year between 1608 and 1648 part of a period sometimes known as The General Crisis, which I would say is an example of historians being terrible at naming things, except that it was a rather general crisis.

From Africa, to Asia, to Europe, to the Americas, there was quite a lot of crisis going on which is a little weird because overall the human species was getting much wealthier and better connected. Like for instance, there was much more silver because European empires especially the Spanish Empire were extracting it from colonies in the Americas.

There was also a much broader range of food available. Rice and wheat had just come to the Americas and everything from pineapples to cassava to potatoes had come to afro-eurasia. And you would think with more money and more food there would be more people. But no.

For one thing the Columbian Exchange also brought devastation. Perhaps more than 90% of Native Americans were killed in the centuries after Europeans arrived mostly from diseases that were new to the Americas like smallpox and diphtheria. That population decline began around 1500 but lasted throughout the general crisis.

And then there was the Atlantic slave trade which was growing throughout the general crisis with horrific consequences of its own. Around 15% of Africans died in slave ships on the journey to the Americas and those who didn't saw their life expectancies severely diminished. And I think it's worth noting that many of the crops that relied on slave labor, like coffee and tobacco, were not necessary to sustain human life. They were basically luxury goods. So maybe more access to luxury goods indicated that humanity was getting wealthier but that doesn't necessarily mean that on average human life was getting better.

In fact, despite the influx of wealth European populations were also declining largely due to the 30 Years War, one of the longest and deadliest wars in European history, which is really saying something. The war killed through combat and famine around 20% of people in what is now Germany and as many as a third of people in what are now Poland and Lithuania. Meanwhile Spain, which had become phenomenally wealthy from all that silver, defaulted on its debts repeatedly during the general crisis because they didn't understand inflation and all that silver caused a lot of it.

But the single biggest contributor to 17th century population decline was the collapse of the Ming Dynasty in China. Between 1600 and 1644 when the Ching dynasty began, China's population decreased by 50 million people. And that was also partly due to humanity's newfound abundance of silver. The Ming government required people to pay taxes in silver which meant more people had to spend more hours working at making goods that could be sold for silver which meant lower agricultural yields. Also, the Ming Dynasty, like Spain, failed to understand inflation, all of which led to famine.

One more thing that made the general crisis so general and crisis-y, at the time earth experienced significant climate change. It's sometimes called the Little Ice Age. Global temperatures dropped on average around one degree Celsius which also contributed to famines. But don't worry it's not like... oh. it is like.

Hank, since the general crisis humanity has experienced its longest ever run of population growth, increased life expectancy, and decreased poverty. But the early 17th century is a reminder that progress is never simple, or universal, or guaranteed. It's a reminder that a changing climate can fuel global instability and that growing connectivity and wealth is only good news for humans once we learn to live with and share that growth.

Hank, I'll see you on Friday.