Wanderlust World Wanderlust World North America has been buried under continental ice sheets multiple times during the Pleistocene Epoch (2.6 million to 11,700 years ago). These glacial cycles—most recently the Wisconsin Glaciation, which ended roughly 10,000 years ago—resulted from a convergence of astronomical, geological, and atmospheric factors.
Cyclical changes in Earth's orbit alter the distribution and intensity of solar radiation:
When these align to produce cool summers at high latitudes, winter snow survives and accumulates into ice sheets.
Over millions of years, North America drifted into polar latitudes, placing large landmasses where snow could persist year-round—a prerequisite for ice sheet nucleation.
Ice core records show CO₂ and methane levels drop during glacial periods (to ~180 ppm CO₂) and rise during interglacials (pre-industrial ~280 ppm). Lower greenhouse gases amplify orbital cooling.
Changes in the Atlantic Meridional Overturning Circulation (AMOC) can reduce northward heat flow, promoting ice growth.
Uplift of the Rockies and other ranges created high-elevation accumulation zones. Once ice forms, its high reflectivity (albedo) cools the region further, driving expansion.
The Laurentide Ice Sheet covered most of Canada and the northern U.S., reaching as far south as Missouri and Ohio. The Cordilleran Ice Sheet blanketed the western mountains. Sea levels dropped ~120 meters, exposing the Bering Land Bridge.
We now live in the Holocene interglacial. Human-caused greenhouse gas increases have likely delayed the next natural glacial inception by tens of thousands of years.