Mary Bachowski, age 11, of Milwaukee, Wisc, for her question:

When will there be another ice Age?

There have been many ice Ages in the long history of the earth, but they have not occurred at regular intervals. We do not know what causes these long chilly periods in the world climate or why they come and go as they do. So we cannot predict when the next ice age will spread its chilly glaciers over large areas of the land.

In the past million years, four ice Ages have gripped the northern hemisphere. The last of them started to recede some 50,000 years ago, and its glaciers are still shrinking from Greenland and the far north. The world climate is getting steadily warmer, and this pleasant trend is expected to continue for thousands Of Years. But no one can tell when or even if an ice Age will strike in the future.