Final answer:
The Medieval Warm Period and the Little Ice Age were influenced by changes in solar activity and volcanic eruptions, which led to significant climatic and social impacts.
Step-by-step explanation:
The two most important climate forcings responsible for the Medieval Warm Period and the Little Ice Age include changes in solar activity and volcanic eruptions.
During the Medieval Climate Anomaly, warmer conditions allowed the Vikings to colonize Greenland due to freer seas of ice.
The Little Ice Age, however, was characterized by cooler temperatures contributing to crop failures, famine, and changes in societal structures due to the advance of glaciers and prolonged periods of drought. Factors such as volcanic eruptions and changes in Earth's orbit led to a global decrease in temperature by about 0.6°C, which was significant enough to impact agriculture and societies significantly.