The most recent Ice age began about around the past time of 1.8+ years ago, lasting only for merely 11,500 years. From that time, glaciers and ice basically covered most of the earth, and today there are ice/frozen lands that still cover the north and south of earth as results of warmer temperature coming around.
Their populations increased dramatically
The item that was NOT a cause of the Reformation:
C. The desire to spread Islam to Western Europe.
Further details:
The Roman Catholic Church failed to provide much hope or comfort to people during the years of the 100 Years War and the devastation of the Black Death. Corruption within the church only became worse in the years that followed, and people were wanting change. Coupled with that were new ideas and challenges being posed by the start of the Scientific Revolution. Martin Luther, whose activity sparked the Reformation, was a contemporary of Nicolaus Copernicus, whose work sparked the Scientific Revolution.