FEBRUARY 15, 2016 3:20 AM

London, 1665. The capital smelled of death in its last large outbreak of the Plague, the worst since the Black Death of the 14th century. The diarist Samuel Pepys mourned, “Every day sadder and sadder news of its increase. In the City died this week 7,496; and of all of them, 6,102 of the Plague. But it is feared that the true number of the dead this week is near 10,000 — partly from the poor that cannot be taken notice of through the greatness of the number.”

As the deaths mounted and the streets filled with waste, Londoners noticed that dogs and cats were everywhere in the city. And so the order went out from the Lord Mayor.

Kill the dogs and cats.

The Chamberlain of the City paid the huntsmen, who slaughtered more than 4,000 animals. But the dogs and cats were chasing the rats that were feeding on the waste — and the rats were carrying the fleas that transmitted the Plague. Now spared from their predators, the rats spread the affliction even more fiercely. The medical advice from London’s College of Physicians — to press a hen hard on the swellings until the hen died — did not slow the disease. In the end, the Plague of 1665 is thought to have killed almost 20 percent of London’s population (the equivalent of a million and a half people today). A great fire then consumed a third of the city.

Many humans and animals died in this crisis of ignorance. Now that we understand the Plague bacterium, we know what procedures and medicines will keep the disease from becoming epidemic. Ignorance, we might say, no longer plagues us.

Today, pestilence threatens us not because of our ignorance but because of the success of our systems. Our transportation networks are now so fast and far-flung that they transmit diseases worldwide before cures can catch up. The next epidemics will play on our strengths, not our weaknesses — fighting them will mean canceling flights, not killing fleas. This Horseman of the Apocalypse has dismounted and now travels coach.

The 20th century marked an inflection point — the beginning of humanity’s transition from its ancient crises of ignorance to its modern crises of invention. Our science is now so penetrating, our systems are so robust, that we are mostly endangered by our own creations. Our bomb-making is now informed by particle physics; our computers are becoming ever-better informed about our private lives.

In 1665, half a billion humans sweated to sustain the species near subsistence with their crude implements. Now our global economy is so productive that 16 times that number — some 8 billion humans — will soon be alive, and most will never have known such poverty.

Indeed, our machines have multiplied so much that a new crisis looms because of the smoke coming off them as they combust. Future food crises, if they come, will be driven by anthropogenic climate change. Famine will descend not from the wrath of God but from the growth of gross domestic product. We ourselves are outfitting the Horsemen of the future, or perhaps it’s better to say that we are creating them.

Our new crises of invention are so challenging because the bads are so tightly bound with the goods. Breaking the world’s slave chains was a moral triumph; breaking the world’s supply chains is not an option. Climate change is a crisis of invention. So many more people, living longer, eating better, traveling more to see the world and one another — is it not poignant that these human goods are engendering a mortal danger?

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