Final answer:
The most important climate forcings for the Medieval Warm Period and Little Ice Age were slight natural variations in temperature. The Little Ice Age's cooling effects, often attributed to volcanic eruptions and orbital changes, had widespread environmental and societal impacts.
Step-by-step explanation:
The Medieval Warm Period and Little Ice Age were significant climate events that occurred due to natural climate forcings. For the Medieval Warm Period, which lasted from around 900 to 1300 AD, slight increases in global temperatures of about 0.10 °C to 0.20 °C above the norm led to the seas being free of ice, which facilitated Viking colonization of Greenland.
The Little Ice Age, particularly profound in the fourteenth century, was a period marked by global cooling that affected the Northern Hemisphere, leading to significant environmental and societal consequences. It is believed to have been triggered by a combination of volcanic eruptions and changes in the Earth's orbit. Massive volcanic eruptions in the tropics may have discharged clouds of sulfate particles into the atmosphere, reflecting solar energy back into space and causing a mean global temperature decrease. This cooling had a ripple effect on agriculture, leading to crop failures, famines, and long-lasting societal impacts such as deforestation due to increased demand for heating resources.