A New North American Ice Age

We tend to think of an ice age in terms of the North American and European ice sheets; since these have disappeared, we think of the present period as being non-glacial.

If we consider the earth as a whole, however, we find that the area covered by present-day ice sheets is over one-third that covered during the greatest extension of the last North American glaciation. The total volume of ice is harder to estimate, but the rates of maximum volume to present volume is probably around 3:1.

From this viewpoint, we can speak of a present glacial period rather than a past one. What would cause the North American ice sheet to re-form? Is it happening?

Under present conditions, there is a considerable amount of snow left at the beginning of winter in the region around Hudson Bay. If this accumulation of ice continues over a long period, it will reach a point where it controls atmospheric movement to such an extent that a new continental ice sheet is inevitable. However, since it takes many thousands of years to build up a major ice sheet, we are not immediately concerned about when it will cross the Canadian border.