Global Climate Change

The Medieval Global Temperature Optimum or the Medieval Warm Period was time of warm climate in the North Atlantic Region from 950 to 1250 AD, affecting California, China and other areas.  Though this was a warm period, it cannot be compared to the warmth we see in present temperatures.
During this time there were severe droughts and rains in different parts of the globe creating. For some it created a difficulty in trying to produce crops and for others it allowed them to produce more crops.

Following this time, was the Little Ice Age, where cooler temperatures prevailed, from 1350 to 1850.  It was not a true ice age but was introduced as the term in scientific litterature by François E. Matthes.  It has been proposed to be caused by cyclical lows in solar radiation, heightened volcanic activity, changes in the ocean circulation, an inherent variability in climate, or decreases in population. 
During this time, much strife was caused. The Little Ice Age created many catastrophes leading to droughts, famines, epidemics and wars.These included the Great Famine, Black Death, Manchu Conquest of China, the Witch Hunts, The Thirteen Year's war, Rise of the Potato, The French Revolution and the Midwestern Population Expansion. 

Both of these periods have left some effects on the global climate change and have led to the results in weather we have today.