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Don Paul: 2018 was rough, but 536 was a nightmare

The year 536 was the beginning of the worst time to be alive … if you managed to live.

You may be familiar with the studies of earth’s past climate conducted by digging up ice cores and examining their many layers for detail on how much volcanic aerosol material was in the air, how much carbon dioxide, how much methane, what temperatures and precipitation were based on samples of plant life and many other elements. The examination of ice cores is part of paleoclimatology.

There are also tree rings to examine growth cycles, tied closely to longer climate changes, fires and shorter weather cycles. And the University of Michigan has gathered and cataloged many boreholes, digging into the earth’s crust to find their samples.

Without listing all the many kinds of samplings into the earth’s geological and climatological past, newer technologies have refined this kind of sampling to lead to confidence that the year 536 was truly a nightmare.

A Harvard medieval historian and archaeologist, along with colleagues, tells Science magazine he's made that determination.

From the Science article:

A mysterious fog plunged Europe, the Middle East and parts of Asia into darkness, day and night — for 18 months. "For the sun gave forth its light without brightness, like the moon, during the whole year," wrote Byzantine historian Procopius. Temperatures in the summer of 536 fell 1.5°C to 2.5°C, initiating the coldest decade in the past 2,300 years. Snow fell that summer in China; crops failed; people starved. The Irish chronicles record "a failure of bread from the years 536–539." Then, in 541, bubonic plague struck the Roman port of Pelusium, in Egypt. What came to be called the Plague of Justinian spread rapidly, wiping out one-third to one-half of the population of the eastern Roman Empire and hastening its collapse, McCormick says.

Now, a multidisciplinary team from the University of Maine is leading what’s being called an “ultraprecise” ice analysis from a Swiss glacier. They found that a cataclysmic volcanic eruption on Iceland in 536 threw massive amounts of ash, sulfur dioxide and other aerosols into the atmosphere in the Northern Hemisphere, followed by two similar eruptions in 540 and again in 547. This set of three powerful eruptions led to drastic cooling that lasted longer than would have occurred from a lone major eruption.

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Shortly thereafter came the terrible outbreak of bubonic plague in parts of Europe, all combining to create one of the worst periods of hardship in human history.

In the next century, the same ice core revealed, came something of a turnaround. A spike in lead in the air was tied to a boom in silver refining, signaling economic recovery.

Previous tree ring studies in the 1990s had pointed to greatly curtailed growth cycles around 540, but the cause wasn’t really known until this ice core analysis pinned down these eruptions.

From these types of analyses, University of Bern researcher Michael Sigl has determined, nearly all exceptionally cold summers in the last 2,500 years have been tied to major volcanic eruptions preceding those summers.

In pursuing this important analytical breakthrough, the University of Maine team was able to extract a 72-meter core from a Swiss glacier. They were able to pinpoint eruptions, Saharan dust storms and increased airborne lead from human activity to mark these kinds of shorter-term climate trends in detail never before possible. Using a laser slicing method in which ice is cut into tiny slivers, more than 50,000 ice samples were drawn from each of the 72 meters in that ice core.

In the meantime, we can hypothesize that a large increase in the number of volcanic eruptions could change the global warming picture in the future. However, there is no evidence yet that such an activity increase is in the offing. Given that, an occasional very large eruption or two could still cause some cooling for a couple of years, as was the case with Mount Pinatubo in the Philippines in 1991.

Those effects, however, don’t persist for very long, and the forces of ongoing warming from human-produced greenhouse gas emissions do persist, and for a long time.

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