View Full Version : The Role of Climate Change in History

03-02-2013, 08:21 PM
The Role of Climate Change in History

Only recently, by comparing tree-ring data, the ratio of oxygen isotopes preserved in old ice (O16 vs. O18), the types of algae skeletons found on the ocean floor, etc., have we been able to measure average world temperatures over the ages, giving us a chance to learn how climate changes have affected history. The most important fact we have learned is that temperatures have not been stable since the ice age ended; they have gone up and down like prices on the stock market. During four prolonged periods in the last 4,500 years, world temperatures were warmer than they are today. Those "warming periods" were:

2500 to 2100 B.C.
1400 to 900 B.C.
1 to 500 A.D.
800 to 1200 A.D.

After each warming period came a time when the earth was colder than it is now, the most famous being the "little ice age" of 1300-1700 A.D. The first warming period neatly corresponds to the early bronze age, and in the case of Egypt, the dates almost perfectly match the dates I use for beginning and end of the Old Kingdom, Egypt's first golden age. The second warming period came during a time archaeologists call the late bronze age, and the cold period in-between the first and second warming periods saw the great Indo-European migration; perhaps the migration itself started because increasing snowfall and colder temperatures forced the Indo-Europeans to leave their original home in the Caucasus mountains. The dates on the third warming period are close to the dates for the rise and fall of the Roman Empire, the following cold period matches the "darkest" part of the Dark Ages, and the fourth warming period caused a population boom in Scandinavia, leading to shiploads of Vikings going forth and terrorizing their neighbors.


Because of longer growing seasons, the warming periods allowed farmers to grow crops that weren't possible at other times; e.g., it was possible to grow grapes in England during the medieval warming period, but not before or since. With larger harvests, the local populations grew to absorb all available food (and then some). Conversely, the colder times saw shorter growing seasons, and an out-of-season killing frost could bring famine. In the pre-industrial world, the economies of most nations were totally dependent on agriculture, so one or more crop failures could cause everything else to unravel. However, not everyone was affected the same way when the temperature changed. This may explain why the Greeks, who preferred trading and fishing because they live in a country with very poor soil, enjoyed their best years during a cold period. One thing is certain; whenever world temperatures suddenly go up or down, there is a change in which nations and peoples are dominant on the world scene.

Historians now believe that late in the third millennium B.C., a climate change helped bring down the Old Kingdom in Egypt, and made it easier for Sargon I and the Akkadians to conquer the Sumerians. The cause of the sudden cooling at that time isn't clear, but a recently discovered crater in southern Iraq, made by a meteor that struck around 2300 B.C., has been suggested as the culprit; heavy volcanic activity is also a possibility.

03-02-2013, 08:35 PM
I was looking for source of this information and found a more updated graph http://sci.rutgers.edu/forum/showthread.php?t=92074

I think it appears the authors have an agenda since the graph looks too prefect. Is it made up data or just highly smoothed out?

EDIT: I found more detailed ranges at but only up to 2000 AD at http://www.longrangeweather.com/Long-Range-Weather-Trends.htm

03-02-2013, 08:56 PM
Thanks I updated the chart per your source.

I don't think the data is made up but it does look as if it smoothed out. The data comes from two Climatologist, Cliff Harris who has been often rated as one of the top ten climatologists in the world for nearly 4 decades and Meteorologist Randy Mann who has been recognized by the American Meteorological Society since 1988.

Here is the link to their site. http://www.longrangeweather.com/

03-03-2013, 02:58 AM
Does anyone here see any credibility in linking sunspot activity to climate change?