WHAT IF? THE ICE AGES HAD BEEN A LITTLE LESS ICY?

The What If? historical book series explores the impact of historical events by presenting counterfactual scenarios, or alternative histories. Most geological events are too remote in time and too indirect in effect for a counterfactual approach to be any more than science fiction. One exception is the Pleistocene, which was recent enough and had dramatic impacts on human history. In this counterfactual scenario, I assume that the North American ice sheets never extended far below the Canadian border, and the Scottish and Scandinavian ice sheets never merged. The impacts of this alternative history include:

1. The Missouri River would not have been diverted into its present course and would probably have re-established its former drainage to Hudson's Bay. The United States would have acquired a much smaller Louisiana Purchase, with no water route for Lewis and Clark to follow to the Pacific Northwest. The western boundary with Canada might well be far south of its present latitude.

2. The Ohio, and probably the Teays paleo-river, would not have been established. The St. Lawrence watershed might have extended far down the west side of the Appalachians. The Thirteen Colonies might well have been hemmed in to the west and confined permanently to the Atlantic Coast. There would be no Great Lakes and no Erie Canal. Without the Ohio and Missouri Rivers furnishing easy east-west water transport, American history would have been profoundly different.

3. If the Scottish and Scandinavian ice sheets had not merged, the ancestral Rhine-Thames system would have flowed unhindered across the North Sea shelf, rather than seeking a new outlet to the west. There would be no English Channel, no defeat of the Spanish Armada, no water barrier to thwart Napoleon or Hitler. Britain might still be a formidable naval power, but with a land frontier as well, its cultural and political independence would have been far less secure.

In conclusion, two relatively small changes in Pleistocene paleogeography would have profoundly changed Western history.