The Roman Period (approximately 300 BC - 400 AD)
*Part of the Early Subatlantic period (300 BC - 750 AD)
The evidence from this time period indicates that in Europe and parts of North America, the climate was relatively mild. There were short-term fluctuations, but overall mild climate conditions prevailed. The evidence of this time period focuses mostly on North America, Europe, and parts of Asia.
North America - temperatures during this time period reached their peak in about 1 AD. These temperatures were preceded by cooler and wetter conditions, which began to change at around 200 BC. Between 200 BC and 300 AD, summers were particularly warm. After 300 AD, cooler and wetter temperatures continued and glacial advances occured in the Rocky Mountains and Sierra Nevada.
Europe - In northern Europe, temperatures were characterized as being cool to mild. The onset of the Roman period was characterized by cool temperatures. A number of severe winters were recorded in Rome during the early Roman period. Temperatures after this were more mild. Between 300 BC and 400 AD glaciers in the Alps were in constant retreat. Towards the end of the Roman period temperatures began to rise.
Sea level during the Roman period dropped from a high around +2 m (relative to modern sea level) in the classical Greece period, to a low around -1 m during the first century AD. This is why today many Mediterranean ports that flourished during the Roman period are now underwater. The low sea level was followed by a progressive rise, which continued after the Roman period.
Northern Europe was particularly moist during this period, and this facillitated the spread of beech forests. The centuries between 350 BC and 100 BC were notably wet in northern Europe. By the first century AD, the pattern of precipitation in Europe and the Mediterranean resembled that of today. This was followed by a wetter period, which ended near the year 350 AD.
Other Aspects of Climate
In northwest Europe during the Roman period, the climate between 300 BC and about 100 AD produced frequent storms and the blowing of sand near the coast. In 120-114 BC the Great North Sea Storm altered the coastline in a sea flood called the Cymbrian flood, which sent people living in the area south.