The little Climatic Optimum

Centuries later the return of warmer and drier weather in Europe was accompanied by a new threat from the mounted nomads of the East. As the forest retreated westwards once again, the advancing steppes gave horsemen a highway into the heart of Europe.

The warming trend which aided the advances of the Huns, the Avars, the Magyars, and the Mongols into Europe reached its peak between AD 700 and 1100, a period called the little Climatic Optimum. After the conclusion of this warmer period the nomads ceased to be a threat to Europe.

Further north the same warming trend enabled the Vikings to settle on the Greenland coast, which was actually green in those days.