“What hath God wrought?”

This quotation from the book of Numbers was suggested by the daughter of the Patent Office Commissioner in 1844 as the first message sent by Morse code from a demonstration before the US Congress to a railroad station in Baltimore. The quote is my question in revisiting the tired old debate about climate change. Is the observable warming of the planet “anthropogenic” (human-caused) or “natural”?

A recent article in the Proceedings of the National Academy of Science (PNAS Dec 14, 2020) details the collapse of an ancient civilization by purely natural causes of warming and drought. Ancient cities often formed around natural rivers providing easy transportation and water for crop irrigation. The great river civilizations of central Asia flourished for 2,000 years with elaborate canals and waterways constructed to irrigate crops.

Until recently, the prevailing theory was that Mongol invasions of the 13th century (CE) led to the collapse of these great civilizations and the Silk Road trade network. The authors of the PNAS study showed that rainfall in the region had declined over two centuries prior to the Mongol invasions. The canals dried up and the great Asian river civilizations of the region deteriorated and the population moved elsewhere. The Mongol invasions were just the last straw on an already dwindling population.

It is possible for warming and droughts to destroy irrigated agriculture. Even our pumping of the Ogallala aquifer will come to an end when it runs dry. At some point, does it really matter if the climate train wreck is anthropogenic or not? If we can see the train coming, shouldn’t we do something about it?

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