Whole story hereWithout the impact of solar radiation, the temperature on the earth would be about the same as the temperature of space, which is about -454 F. The amount of radiation reaching the earth is about 1,368 watts per square meter. This is a vast amount of energy, which would require the simultaneous output of 1.7 billion of our largest power plants to match. About 70 percent of this solar energy is absorbed and 30 percent is reflected. However, the amount of solar energy reaching the earth is not constant, but varies in several independent cycles of different degrees of magnitude, which may or may not reinforce each other.
These cycles include a 100,000-year cycle, which results from the elliptical orbit of the earth around the sun, a 41,000-year (obliquity) cycle, which results from the tilt of the earth on its axis, a 23,000-year cycle which results from "climatic precession" or changes in direction of the earths axis relative to the sun, and an 11-year sunspot cycle, during which solar radiation increases and then declines. The most recent sunspot radiation cycle peaked in the year 2000, and currently is approaching a minimum. Curiously, NASA and the Russian Observatory both report that total solar radiation now has peaked, and all these cycles may be simultaneously in decline
Each 100,000-year peak in radiation appears to last about 15,000 to 20,000 years, and each has been coincident with massive surges of carbon dioxide and methane (the green house gasses), into the atmosphere, causing de-glaciation of the Polar and Greenland ice caps. Surges of these greenhouse gasses have always been vastly greater than the amounts currently being generated by burning fossil fuels. For example, the most recent 100,000-year cycle raised sea levels 400 feet in the first 10,000 years, but since then sea levels have risen very little. In the current warming period, sea levels are rising only about 3 millimeters per year, and temperatures over the last 100 years have risen a modest 0.6 of a degree C.
Superimposed on this latest 100,000-year peak have been 6 secondary warming periods, each coincident with additional surges of carbon dioxide and methane, lasting about 200 years and then subsiding. Each of these previous warming periods was warmer than the current warming period, and current temperatures are below the median for the last 3000 years. Most remarkably, civilization first emerged in the Tigris, Euphrates and Nile River Valleys about 3400 B.C. in that period of great warming, and even more remarkably, each of these secondary surges of greenhouse gasses (none of human origin), has also been coincident with the rise of a major civilization.
For instance, 3,000 years ago in the 1000 B.C. warming period, the Babylonian era emerged. Then, 500 years later, the Greek civilization flourished, followed by the Romans 400 years later. A 1,000-year cold period followed through the dark ages, but then in the very warm 1000 A.D. Medieval Period, the ice and snow melted on Greenland; the Danes farmed there for 200 years, until it froze over again. There are no reports of seaports being flooded during this warm period.
About 500 years after the Medieval period, another surge of greenhouse gasses initiated the Renaissance, which was followed by an unexplained "Little Ice Age" from about 1600 to about 1750. (This was coincident with the Maunder Solar Radiation Minimum). During this period, Europe was covered with ice and snow, growing seasons were short, and starvation was common. Farmer unrest may have triggered the French Revolution. The most recent warming period began as solar radiation rapidly increased.