Smallpox and the Little Ice Age

Via Analog Science Fiction and Fact: Richard A. Lovett's column on "The Ice Age That Wasn't" in the April issue was partly drawn from Plows, Plagues, and Petroleum by William F. Ruddiman. An Amazon reviewer explains Ruddiman's smallpox connection:

He proposes that major plague pandemics have caused sufficient die-offs, abandonment of farms, and reforestation to temporarily lower CO₂ and temperature. This could explain the later-Roman/Dark Ages lower temperatures, followed by the relatively disease-free Medieval Warming Period, in which Greenland was settled, and UK vineyards spread again to current levels, if not quite as far as early Roman. He ascribes the Little Ice Age drop to Bubonic plagues in Europe, and especially, to the death of estimated 50 million native Americans from smallpox and other European diseases.