When the Medieval Warm Period Ended, Sea Ice Sealed Off Greenland and Nearly Wiped Out Iceland

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During the Medieval Warm Period, the North Atlantic was navigable in ways it is not today. Ships could sail from northwestern Europe to Iceland and on to Greenland along routes that were reliably ice-free. Norse settlements took hold in Greenland precisely because the climate permitted it.

When the Medieval Warm Period gave way to the Little Ice Age, that changed rapidly. Polar sea ice extended dramatically further south, sealing off Greenland entirely - cutting the settlements off from resupply and contact with Europe, contributing to their eventual extinction. Iceland came close to the same fate. Agriculture collapsed under the returning cold. Trade networks that had depended on accessible sea routes were severed. The human cost was severe and sustained.

Randall Carlson draws the broader conclusion that the historical record consistently supports. Cold periods have always extracted a far heavier toll on human civilisation than warm ones. The disruption of agriculture, the closing of trade routes, the displacement of populations, the spread of famine and disease - these follow cold, not warmth. It is a pattern the geological and historical record repeats without exception, and one Randall considers essential context for any honest assessment of what climate change in either direction actually means for human societies.