When Eric the Red led the Norwegian Vikings to Greenland in the late 900s, it was an ice-free farm country--grass for sheep and cattle, open water for fishing, a livable climate--so good a colony that by 1100 there were 3,000 people living there. Then came the Ice Age. By 1400, average temperatures had declined by 2.7 degrees Fahrenheit, the glaciers had crushed southward across the farmlands and harbors, and the Vikings did not survive.
Such global temperature fluctuations are not surprising, for looking back in history we see a regular pattern of warming and cooling. From 200 B.C. to A.D. 600 saw the Roman Warming period; from 600 to 900, the cold period of the Dark Ages; from 900 to 1300 was the Medieval warming period; and 1300 to 1850, the Little Ice Age.
Many things are contributing to such global temperature changes. Solar radiation is one. Sunspot activity has reached a thousand-year high, according to European astronomy institutions. Solar radiation is reducing Mars's southern icecap, which has been shrinking for three summers despite the absence of SUVS and coal-fired electrical plants anywhere on the Red Planet.
Comment: a helpful view of the so-called "global warming" crisis. Puts it into perspective!