January 30, 2012 | 39
Humanity has weathered many a climate change, from the ice age of 80,000 years ago to the droughts of the late 19th century that helped kill between 30 and 50 million people around the world via famine. But such shifts have transformed or eliminated specific human societies, including the ancient Sumerians and the Ming Dynasty in China, as highlighted in a review paper published January 30 in Proceedings of the National Academy of Sciences.
Epidemiologist Anthony McMichael of Australian National University surveyed how human societies fared during previous episodes of extreme weather brought on by climate shifts. The big threat is changes to food production, or as McMichael puts it “the drought-famine-starvation nexus.” And we’ve never weathered a climate change so big, so rapid and so widespread as the one we are now busily creating by burning fossil fuels, notes McMichael.
Long-running climate changes have often brought about the downfall of cultures, including foiling the earliest human attempts at settled farming nearly 13,000 years ago. Around that time, a major millennia-long climate cooling event known as the “Younger Dryas” coincides with the end of most settlements along the Nile Delta and in modern-day Syria. Skeletons from the era evince “an unusually high proportion of violent deaths, many accompanied by remnants of weapons,” McMichael noted. More recently, three back-to-back decades-long droughts afflicted Mayan society in Central America between roughly 760 and 920 CE, and marked the end of that culture’s regional dominance.
Shorter term climate changes have proven equally devastating. Decade-long droughts in 17th century China led to starvation, internal migration and, ultimately, the collapse of the Ming Dynasty. A seven year span of torrential rains, attendant floods and cold in the early 1300s helped cause a famine that may have killed as much as 10 percent of the people in northern Europe—a generation that would then face the Black Death a few decades later.
Even a single bad summer can be enough—like the hot summer of 1793 in Philadelphia that, paired with an influx of refugees from modern day Haiti, saw an outbreak of yellow fever that killed tens of thousands.
Of course, none of these societies had the benefits of modern technology or modern energy, whether medicine or air conditioning. But even that may not be enough to offset the roughly 2 to 4 degrees Celsius of warming in average global temperatures the world is on pace to achieve via emissions of greenhouse gases. “Such a change will surely pose serious risks to human health and survival,” McMichael wrote, “impinging unevenly, but sparing no population.”
Image: Sumerian cuneiform via © iStockphoto.com / Michael Fuery