Final answer:
The subtle warming of the Medieval Climate Anomaly, characterized by temperatures 0.10 to 0.20°C higher than average, allowed agricultural advancements and the Vikings to colonize Greenland.
Step-by-step explanation:
The Medieval Climate Anomaly occurred between 900 and 1300 AD. During this period, the slight increase in temperatures by 0.10 to 0.20°C above the average led to various changes. This subtle change freed seas of ice, which notably allowed the Vikings to colonize Greenland. This period, characterized by a warmer climate, contrasts with the Little Ice Age that followed, where a slight cooling led to crop failures and famine.
Consequently, within the list of the provided options, the correct answer is a) Expansion of polar ice caps is incorrect as the period saw a reduction in ice. b) Migration of polar bears to warmer regions is unlikely to be directly related to the Medieval Climate Anomaly. c) Agricultural advancements and population growth is correct as the slightly warmer temperatures would have facilitated agriculture and supported population growth. d) Decreased sea levels is incorrect as the warmer temperatures would have reduced polar ice caps, potentially leading to sea level rise.