Variability has been a dominate mode throughout climate history

Russ Steele

I have been researching the social and political impacts of the last Grand Minimums, including the Dalton and the Maunder. I am currently reading Brian Fagan’s, The Little Ice Age: How Climate Made History 1300-1850.

It is clear that even during the Little Ice Age (LIA) the global temperatures varied widely with warm years and very cold years.  Year will lots of moisture, and years that were dry.  Problems rose for populated regions when there were multiple cold or very wet years in a row, or long periods of drought. The result was  crops failures. With limited year to year food and fodder storage it was hard to sustain enough food stuff to feed the existing population in many regions. Others were challenged, but managed to weather the storm of lower agriculture production.

To examine this variability, here is a plot from the average mean temperature in Central  England, compiled by Manley, Parker and Horton, published in the International Journal of Climate.  This is one of the longest recorded temperature histories from 1659 to 2010.

 The purple line represents the end of the Maunder Minimum, the two blue lines bracket the Dalton Minimum.

 To bring the variability issue closer to home, I took a look at the reconstructed flow of the Sacramento River from tree ring data developed by David Meko for the California Department of Water Resources, July 2001.

This flow shows the droughts in the Sacramento river drainage from 903 to 1903 . The major droughts are noted on the graphic.

When looking at the temperature and drought graphics please note that there were multiple years in a row when temperatures were below, or above, the mean. It is easy to see there were multiple drought years,  some as long as 25 years.

The important message to take away from the above plots is the variability, there are warm years and cold years, wet years and dry years, all riding on top of longer term trends.

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