Old climate traces shed new light on history

This story originally appeared on Yale Environment 360 and is part of Climate desk Cooperation.

Joseph Manning, a professor of ancient history at Yale University, likes to recall the moment when he was shown a preview of a scientific paper pointing to the time of major volcanic eruptions over the past 2,500 years. When he read the newspaper: “I literally fell off the chair,” he said recently.

Based on new geochemical techniques for analyzing ice core sediment to determine the dates of ancient volcanic activity down to the year or even the season, the paper, published in Nature in 2015 showed that major eruptions worldwide caused abrupt, up to ten-year-long decrease in global temperatures. Later research put these drops to as much as 13 degrees F.

What amazed Manning, an Egyptologist, was that the paper recalibrated previous chronologies by seven to eight years, so that the dates of the eruptions coincided nicely with the time of well-documented political, social, and military upheavals through three centuries of ancient Egyptian history. The paper also correlated volcanic eruptions with larger 6th century AD pandemics, famine and socio-economic unrest in Europe, Asia and Central America. The inevitable conclusion, the newspaper claimed, was that volcanic soot – which cools the soil by protecting its surface from sunlight, adversely affecting the growing season and causing crop failure – helped drive these crises.

Since then, other scientific articles that rely on paleoclimatic data – most of them drawing on advanced technologies originally designed to understand climate change – have found countless cases where climate change helped trigger social and political turmoil and often collapses. The latest is a paper published last month in Communication Soil and environment which stated “a systematic link between volcanic eruptions and dynastic collapse over two millennia of Chinese history.”

The study showed that 62 out of 68 dynastic collapses took place shortly after volcanic eruptions in the northern hemisphere, a result that only had a chance of one in 2,000 happening if the eruptions and collapses were not related. Chinese have traditionally cited the withdrawal of the “heavenly mandate” to explain the cold weather, droughts, floods and agricultural failures that seemed to accompany the fall of dynasties. The newspaper claims that these phenomena have a climatic explanation.

All of these papers are driven by a nearly decade-long revolution in climate science technology. A blizzard of quantitative data from “climate proxies” – ice cores, tree rings, cave stalagmites and stalactites, and lake, bog and seabed sediments – has changed the way some historians carry out their work.

Joe McConnell, who runs a groundbreaking analytical core research laboratory at the Desert Research Institute in Reno, Nevada, believes that climate data offers historians what DNA evidence provides the judicial system: an indisputable, objective source of crucial information. Like DNA evidence refuting a guilty verdict, McConnell said climate data is information that historians “must take in.”

To leverage this data, some historians cross extensive barriers within their discipline to work with biologists, geologists, geographers, paleoclimatologists, climate models, anthropologists, and others. These mold-breaking historians teach geochemistry and climatology; the scientists they work with read history.

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