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William H. Calvin, A Brain for All Seasons:  Human Evolution and Abrupt Climate Change (University of Chicago Press, 2002). See also

copyright ©2002 by William H. Calvin
ISBN 0-226-09201-1 (cloth)    GN21.xxx0     
Available from or University of Chicago Press.
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This 'tree' is really a pyramidal neuron of cerebral cortex.  The axon exiting at bottom goes long distances, eventually splitting up into 10,000 small branchlets to make synapses with other brain cells.
William H. Calvin

University of Washington
Seattle WA 98195-1800 USA

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To:                  Human Evolution E-Seminar
From:             William H. Calvin
52.309°N   4.767°E    -2m ASL
                        Layover Limbo (again)
The Little Ice Age and its witch hunts


Our civilizations began building immediately after the last great continental ice sheets melted about 10,000 years ago, thanks to agricultural success.  Our present warm period has been relatively mellow for the last 8,000 years, with fewer fluctuations than any other similar period in the climate record.  The “Little Ice Age,” a cooling of less than one degree that lasted from the early Renaissance to the middle of the nineteenth century, was small stuff in comparison to the ice ages or the abrupt jumps.

     But the Little Ice Age has a human scale.  You can recognize it by extrapolations from bad storms and droughts in 20th century newsreels and television. “The Little Ice Age,” the archaeologist Brian Fagan writes, “reminds us that climate change is inevitable, unpredictable, and sometimes vicious.”  So it is worth a few pages on the Little Ice Age and contemporary crop failures, just to give you an emotional base, one from which you might conceivably manage to further extrapolate to abrupt climate flips lasting centuries with tenfold greater temperature excursions and far more widespread disruption of ecosystems.

The Little Ice Age as a term is a little vague.  Its first recorded use in 1939 was a very informal analogy, not a serious attempt at naming, and it covered the last 4,000 years!  The term probably caught on as a description of 1300-1850 because our images of those times came from paintings of ice skaters on the rivers of Europe and tales of people walking across the frozen Baltic between Denmark and Sweden.  Books on the subject feature the detailed wintertime scenes painted by Peter Breughel the Elder during the first great winters of the Little Ice Age about 1565.  An exaggerated winter seems to be what we carry away from the subject, what remains after we have forgotten the details.  Even historians are unhelpful.  You can read an excellent history of the last five centuries, such as Jacques Barzun’s From Dawn to Decadence, without finding the Little Ice Age mentioned even once.

     And the average temperature changes of the Little Ice Age seem small – what’s a degree or so, anyway?  None of us are used to dealing in yearly average temperatures, and the annual mean temperature hides the combination of a cold winter and a hot summer.  Because the means are never reported, we have no sense of how much a warm year differs from a cooler year.  We have the same problem in judging how much difference several degrees of global warming will make to our lives.

     By focusing on temperature per se, we conveniently ignore the more important aspects of climate change:  floods, droughts, high winds, dust storms, and unseasonable weather that ruins harvests and sets up famines.  Unsettled extremes are also what the Little Ice Age was all about.  They are what cause people to starve, not what the thermometer reads.

     The most obvious causes of droughts are changes in the winds, what happens with almost any climate change scenario.  Afternoon heating of inland regions causes air to rise, attracting in moist air from offshore which, upon warming and rising itself, dumps its moisture.  Such monsoon winds often fail for years.  Millions of people in India died in the monsoon failures of the late 19th century, and relief efforts in earlier such famines were hampered by the lack of transportation infrastructure.

     In the 1930s, there were particularly strong westerly winds in the U.S.  This extended the rain shadow of the Rocky Mountains farther eastward and reduced the monsoons from the Gulf of Mexico, resulting in the Dust Bowl conditions.

     Lack of winds can also block rains:  a persistent high pressure system, not an uncommon occurrence, blocked weather systems that might have brought rain to the American Midwest and East in the summer of 1988.  Searing heat caused at least half of the grain crops to be lost in the northern Great Plains states.  Long stretches of the Mississippi River became so shallow that barges were stranded on mud banks for weeks.  Huge forest fires burned major sections of Yellowstone National Park that year.

     When this much damage can be done in a single year, just remember that serious droughts endure for decades. When people are told to stop watering their lawns because of a water shortage, they escalate (in the manner of sports hyperbole)  to use the same word, drought, as is used for far more serious conditions, on a far vaster scale and lasting many years – such as the 1930s Dust Bowl or those three Little Ice Age droughts amidst good times in East Africa, lasting 30, 65, and 80 years.

     Besides lack of rain, famines can occur from other climatic causes, thanks to our reliance on agriculture to support a thousand times greater population than before agriculture.  Too much rain at the wrong time can flatten wheat fields, one of the reasons why the Irish shifted from a reliance on grains to less chancy potatoes.  Potatoes were a huge success and the Irish population grew.  But the over reliance on potatoes left Ireland vulnerable to a potato blight that crossed the Atlantic Ocean in the 1840s, causing (together with the ineptitude and unfettered trade ideology of the British government) the deaths of over a million Irish.  Far greater famines occurred in the twentieth century exacerbated by politics, such as the Volga famine of 1921 and the Ukrainian famine of 1932-33.

     In addition to the miseries from famine and its associated diseases, people created their own miseries, driven by a frantic urge to “do something.”  Scapegoating surged as people blamed other people for their misfortunes.  Americans tend to look with suspicion on the Puritans because of the Salem witch trials without realizing that this type of scapegoating was endemic earlier all across Europe and not peculiar to the Puritans.  It coincided with the demoralization produced by the worst years of European climate change.

     Fagan notes that “As scientists began to seek natural explanations for climatic phenomena, witchcraft receded slowly into the background.”  While I hope it stays there, remember that most people still believe in horoscopes – and that most Americans have only rudimentary science literacy.  The rational aspects of civilization are a thin veneer and scapegoating, perhaps escalating to genocide, could still happen in future climatic crises.


Famine followed famine bringing epidemics in their train; bread riots and general disorder brought fear and distrust.  Witchcraft accusations soared, as people accused their neighbors of fabricating bad weather…. Sixty-three women were burned to death as witches in the small town of Wisensteig in Germany in 1563 at a time of intense debate over the authority of God over the weather. . . . Between 1580 and 1620, more than 1,000 people were burned to death for witchcraft in the Bern region alone.  Witchcraft accusations reached a height in England and France in the severe weather years of 1587 and 1588.  Almost invariably, a frenzy of prosecutions coincided with the coldest and most difficult years of the Little Ice Age, when people demanded the eradication of the witches they held responsible for their misfortunes.

-Brian Fagan, The Little Ice Age, 2000



Nothing is more terrible than to see ignorance in action.

- Johann Wolfgang von Goethe


Science is an attempt, largely successful, to understand the world, to get a grip on things, to get hold of ourselves, to steer a safe course. Microbiology and meteorology now explain what only a few centuries ago was considered sufficient cause to burn women to death.

- Carl Sagan, 1996




Notes and References
(this chapter
corresponds to 
pages 205 to 209 of the printed book)

Copyright ©2002 by
William H. Calvin

The nonvirtual book is
available from
or direct from
 University of Chicago Press

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All of my books are on the web.
You can also click on a cover for the link to

Conversations with Neil's Brain:  The Neural Nature of Thought and Language (Calvin & Ojemann, 1994)

The Cerebral Code:  Thinking a Thought in the Mosaics of the Mind (1996)

How Brains Think:  Evolving Intelligence, Then and Now (1996)

Lingua ex Machina:  Reconciling Darwin and Chomsky with the Human Brain (Calvin & Bickerton, 2000)

The six out-of-print books are again available via Authors Guild reprint editions,
also available through (click on cover):

Inside the Brain

The Throwing Madonna:  Essays on the Brain

The River That Flows Uphill


The Cerebral Symphony

The Ascent of Mind

How the Shaman Stole the Moon