This period in history is called the Little Ice Age. The generally cold climate of the period is confirmed in the records of their grape harvests kept by French winemakers for the past 500 years. Geological records suggest that the first Ice Age ocurred about 2.3 billion years ago and the most recent Ice Age extended from about 22,000 through 12,000 years ago. During that time, glaciers covered much of the north including Canada and northern Europe and Asia. Global temperatures were about 10 degrees F. cooler than today.
Studies seem to show that climate changes can be surprisingly abrupt.
It seems an ice age can develop in as short a period as an average human life span. Some scientists believe that we are overdue for the development of another ice age. During the Pleistocene era, extending back about 600,000 years there were four ice ages and in between these the temperature was about 5 degrees F. warmer than today. Before that time, going back about 100 million years to the Cretaceous period, global temperatures appear to have been perhaps 18 degrees F. warmer than today. Ocean levels rose and water spilled over onto the land creating differently shaped land masses.