Earlier papers in this series introduced methods of studying past climate change, the historicity of the Little Ice Age as well as the Medieval Warm Period, the importance of the Little Ice Age in understanding climate change and constraining climatic models, and the importance of the North Atlantic region in understanding and applying constraints on climatic and glacial models. Earlier papers included summaries of the effects of the Little Ice Age in Iceland, Norway, and Greenland. This paper presents an analysis of how the Little Ice Age climate-change record should constrain paleoclimatology and speculations on potential climatic-forcing mechanisms.