In which John Green teaches you about the Little Ice Age. The Little Ice Age was a period of global cooling that occurred from the 13th to the 19th centuries. This cooling was likely caused by a number of factors, including unusual solar activity and volcanic eruptions. The Little Ice Age greatly impacted human social orders, especially during the 17th century. When the climate changed, and the weather became unpredictable, the world changed profoundly. Poor harvests led to hunger, which led to even less productivity, which even resulted in violent upheaval in a lot of places. All this from a little change in the temperature? Definitely.