Even more compelling is the fact that there exists a well-documented Roman Warm period from the time of the Roman Caesars, and a Medieval Warm Period, both of which correlate with solar activity, but certainly can have nothing whatever to do with CO2 produced by any human industrial activities.
Further, earlier global warming periods were always accompanied by great human prosperity, and not by gloom and doom, as today's global warming adherents are forever saying. In fact, it was periods of global cooling that were bad for the world's population and for the environment as a whole.
In AD 793, the Vikings burst upon their European neighbours, starting with England. One venture took them into eastern Europe. There, they founded the Russian State at Kiev, in Ukraine, in 882 AD.
They also moved into France, as the Normans, and became a power in the Mediterranean as well as in Europe.
Two centuries of global warming then followed, from about 930 AD. This warm weather assisted the Vikings in taking Iceland from the Irish. The Vikings settled in Greenland and explored as far west as Newfoundland, in North America.
During this period, around 1000 AD, grain grew in northern Norway and grapes in northern England. The signs of warm-weather crops in these settlements puzzled modern archaeologists when they found evidence of these crops in what they thought had always been an iced-over region.
High in the mountains in central Europe, abandoned ancient mines were reopened when the area thawed. In what was thought of as the arid region of New Mexico, Amerindians of the Anasazi ethic group built canyon towns and irrigated crops as the climate warmed and rain became a regular feature of the area.
Rain also soaked the grasslands of Asia during the warm centuries, and nomadic horsemen thrived. This was great for the nomads but not so great for some of the other tribes in the region, who got beaten up by the nomads, who then acquired great mobility over the grasslands covered in food for the horses.
In China, a magnetic compass was invented – the earliest practical compass was described in a Chinese military manual of 1044. It was a magnetised fish shape that floated on water. Compasses soon evolved into magnets hanging on silk threads. The importance of the compass is that it allowed people to confidently sail far away from land in small ships.
Administrative reforms in China, starting in 1068, transformed the Chinese empire into the first economy managed on modern lines, relying on equitable money taxes rather than forced labour. The economy and the population boomed during the warm years, and government loans encouraged farmers to plant a new variety of rice from Indochina.
The Chinese seafarers continued to trade widely across South-East Asia and so spread their knowledge and goods, to the benefit of all.
In the meantime, in Middle America, around 1200, there was turmoil. Aztecs, from the north, entered the Valley of Mexico. They rose to power over their neighbours in about 1320.
It appears the reason why they moved and rose to power was the downturn in the climate, which began in about 1190. "Hey man, chill out" had a different meaning for them. Other sufferers from the cooling climate were the Anasazi, who were then forced, by drought, to abandon their canyon settlements. They moved to concentrate along the Rio Grande.
Starting in 1314, Europe was struck by repeated famines. The mountain mines were abandoned again, and the Vikings were frozen out of their settlements. By 1342, the Vikings' customary route to Greenland had been blocked by ice.
The Eurasian steppes became the scene of terrible military events. When the rainfall diminished from 1160, the numerous horsemen were happy for a warlord to tell them to attack the farming villages.
The break-out of the Mongols and their allies, the Turks, exceeded any previous break-out in ferocity and scope. In 1211, the Chinese Wall was breached. Baghdad, amid its decaying irrigation works, fell in 1258 to the Mongols.
A crash in the population of medieval Eurasia, already evident in China by 1290, was made worse by disease carried by the Mongol supply and trading caravans.
The Black Death first appeared among the Chinese in 1331, killing more than a quarter of them, and in 1346 a Mongol army in southern Russian spread it to Europe.
The Medieval Warm Period was past, and the Little Ice Age was really on its way.