Causes of the Little Ice Age
 
    It is difficult to assign one cause to the Little Ice Age.  The period was marked by many warming and cooling cycles within itself.  Each of these individual warming and cooling periods could have been caused by any number of events.  According to Kerr, 2001, it appears that the Earth has experienced a Little Ice Age about once every 1500 to 2000 years.  Evidence has been found that suggests ice-borne rock fragments have been found in North Atlantic sediment, and that these same bits appear in layers of sediment about every 1500 years.  These rock fragments are most likely transported by glaciers during cooling periods like the Little Ice Age and then broke away from land locked in the sea borne ice of the glacier.  Evidence of this 1500 year cycle has led some scientists away from the idea that a cooling event like the Little Ice age could be caused only by a change in volcanic activity.
 
    Volcanic activity is a likely cause for some of the more brief cooling events during the Little Ice Age.  One such eruption occurred in 1600 in Peru, which caused the most severe cooling event recorded in the Northern Hemisphere (Aber, 2008).  Iceland experienced two major eruptions in 1693 and 1783, which caused massive destruction.  The cooling caused by volcanic ash after a massive eruption cannot be denied, but the effects are often short term, and climate returns to normal within a few years.  It has been suggested by some scientists (Robock, 1979) that volcanic activity is the most reasonable suggestion for the cause of the Little Ice Age.
 
    Another suggested cause of the Little Ice Age is solar activity oscillations.  It has been documented that the sun experiences cycles in activity.  Solar activity varies on a short term cycle of about 11-13 years (Lerner, 2003).  Solar activity has been correlated to sun spots.  Sun spots are dark spots that appear on the sun and are related to disruptions in the Sun’s magnetic field.  During the Little Ice Age, shortly after Galileo observed sun spots for the first time, there was a relatively long period when no sunspots were observed.  During this same time, the Aurora Borealis (Northern Lights) did not appear over the northern sky.  The Aurora is generally associated with periods of high solar activity.  There is recent evidence of a relationship between Earth’s climate and solar cycles.  Tree ring evidences suggests a growth cycle of 11-13 years which matches the short term solar cycles that are well established.  Cycles that occur over longer periods such as the 1500 year cycle suggested are also possible and are likely causes of such cooling events as the Little Ice Age.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The illustration above taken from http://science.nasa.gov/headlines/y2006/10may_longrange.htm illustrates sunspot cycles that have been recorded in the past.  Evidence of differences in sun spot intensity is indicated by the difference in height between cycle number 20 and 21.  
 
 
 
The image above shows a painting by Birman shortly after the glacial maximum during the Little Ice Age.  The picture on the right was taken by M. J. Hambrey in 2000.  The arrows indicate reference points to indicate glacial recession.  Image taken from http://www.swisseduc.ch/glaciers/glossary/little-ice-age-two-en.html via creativecommons.org.  
 
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