Natural Climate Change

Throughout time, Earth's climate has been ever changing.  Some of Earth's historical climate changes are a bit infamous.  The mass species extinctions that mark the end of the Cretaceous period due to major rapid changes in climate is one of the more well known examples of climate change.  The contributing factors to this extreme shift are generally agreed upon as either meteorites or volcanoes, or perhaps a combination of both.  Either way, the gases and ash released into the atmosphere by these events created an enhanced greenhouse effect.  Subsequently this caused a global temperature increase of about 5°C.  It was this event that wiped out most of the dinosaurs of this period.  More reading on this subject can be found here and here.

photo credit: PA

The "Little Ice Age" between the 17th and 19th centuries is a more recent example of natural climate change, although less extreme than the Cretaceous example.  This period was exemplified by unusually cool temperatures probably caused by decreased solar activity and had a profound effect on human populations around the world, most notably recorded in European history.  The unusual weather had profound effects on agriculture, with many places experiencing food shortages and famine.  This led to social unrest in some parts of Europe and also population losses in some instances.  More extensive information about the implications of the "Little Ice Age" can be found here and here, as can good references for more in depth research.

One of the contributing factors to the "Little Ice Age" was decreased solar activity, which is referred to the Maunder Minimum.  The sun goes through a normal 11-year cycle of sunspots where the number of sunspots oscillates up and down.  During the 1600s and 1700s this oscillation remained unusually low and a very small number of sunspots were observed during this period.  It was this low point in sun spots that is the Maunder Minimum.  The 11-year cycle can be seen in the red line in the graph below.  More about solar cycles can be found here.

Source: USGCRP (2009)