The year without a summer

During the Roman era the climate was rather warm, and we have proof of this from the pools that Ancient Romans used to breed eel. In fact these pools had two holes, one at high tide level and the other at low tide level. At high tide fresh sea water would come in through the first hole while stagnant water left the pool through the second one at low tide, so that the pools had a constant fresh water turnover which worked the same way as modern day aquarium filtering systems. Tides in the Mediterranean sea range approximately 20 cm. so we can know exactly where the sea level was at in those times and consequently we also know what the climate was like.
In history we are told that in 218 b.c. Hannibal crossed the Alps with elephants, which gives us a reason to believe that at that altitude there was no snow, or better yet, perennial snow was easily accessible as opposed to nowadays.
In the Middle Ages they had a long warm period that spanned more or less from the 9th to the 12th century. At the time grapes were grown in England, 500 km further north compared to today.
From about 1200 to about 1850, Earth went through a long cold phase which affected particularly Europe. The Vikings left Greenland where the ports were blocked by ice. The glaciers crept forward and many alpine valleys were abandoned. This is the coldest time in the past 8,000 years, and is in fact called the “Small Glacial Era” and 1816 will go down in history as the year without a summer: In paintings from the 1700s Venice is portrayed as being completely frozen and Bethlehem is covered with snow. Apparently, even during the famous Waterloo Battle, heavy rains had blocked Napoleon and left his cavalry troops stranded in the mud.
After that the temperature rose until it reached its peak in 1950.
Between the Small Glacial Era and today average temperatures have risen by 0.5 – 1.0 degrees. World glaciers are shrinking while sea levels are rising by about 2 mm. per year. This is the global warming which apparently has been caused by man. According to some scientists such as those from ICRAM (Istituto Centrale per la Ricerca Scientifica e Tecnologica Applicata al Mare), the current phase might indicate a part of the hot/cold cycle with a normal rise in temperatures following a cold phase which peaked, as we mentioned, during the first half of the 19th century, one of the most obvious in the middle and recent Holocene age.

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