Dept. of Geology, Western Washington University on the Watts Up With That? blog:
Temperature changes recorded in the GISP2 ice core from the Greenland Ice Sheet (Figure 1) (Cuffy and Clow, 1997) show that the global warming experienced during the past century pales into insignificance when compared to the magnitude of profound climate reversals over the past 25,000 years. In addition, small temperature changes of up to a degree or so, similar to those observed in the 20th century record, occur persistently throughout the ancient climate record.He goes on to review the climate changes during the last 3000 years during the historical era. Fascinating stuff.Figure 1. Greenland temperatures over the past 25,000 years recorded in the GISP 2 ice core. Strong, abrupt warming is shown by nearly vertical rise of temperatures, strong cooling by nearly vertical drop of temperatures (Modified from Cuffy and Clow, 1997).Some of the more remarkable sudden climatic warming periods are shown listed below (refer also to Figure 1). Numbers correspond to the temperature curves on Figure 5.
1. About 24,000 years ago, while the world was still in the grip of the last Ice Age and huge continental glaciers covered large areas, a sudden warming of about 20°F occurred. Shortly thereafter, temperatures dropped abruptly about 11°F. Temperatures then remained cold for several thousand years but oscillated between about 5°F warmer and cooler.
2. About 15,000 years ago, a sudden, intense, climatic warming of about 21°F (~12° C;) caused dramatic melting of the large ice sheets that covered Canada and the northern U.S., all of Scandinavia, and much of northern Europe and Russia.
3. A few centuries later, temperatures again plummeted about 20° F (~11°C) and glaciers readvanced.
4. About 14,000 years ago, global temperatures once again rose rapidly, about 8° F (~4.5°C), and glaciers receded.
4. About 13,400 years ago, global temperatures plunged again, about 14° F (~8°C) and glaciers readvanced.
5. About 13,200 years ago, global temperatures increased rapidly, 9° F (~5°C), and glaciers receded.
6. 12,700 yrs ago global temperatures plunged sharply, 14° F (~8°C) and a 1300 year cold period, the Younger Dryas, began.
7. After 1300 years of cold climate, global temperatures rose sharply, about 21° F (~12° C), 11,500 years ago, marking the end of the Younger Dryas cold period and the end of the Pleistocene Ice Age.
For example, from this latter material here is his bit on the "Little Ice Age":
The Little Ice Age (1300 A.D. to the 20th century)This is a good antidote to the "global warming" hysteria. From his conclusion:
At the end of the Medieval Warm Period, ~1230 AD, temperatures dropped ~4°C (~7° F) in ~20 years and the cold period that followed is known as the Little Ice Age. The colder climate that ensued for several centuries was devastating (see e.g., Grove, 1988, 2004; Singer and Avery, 2007; Fagan, 2000). Temperatures of the cold winters and cool, rainy summers were too low for growing of cereal crops, resulting in widespread famine and disease. When temperatures declined during the 30–year cool period from the late 1940’s to 1977, some climatologists and meteorologists predicted a return to a new Little Ice Age.
Glaciers expanded worldwide (see e.g., Grove, 1988, 2004; Singer and Avery, 2007). Glaciers in Greenland advanced and pack-ice extended southward in the North Atlantic in the 13th century. The population of Europe had become dependent on cereal grains as a food supply during the Medieval Warm Period and when the colder climate, early snows, violent storms, and recurrent flooding swept Europe, massive crop failures occurred. Three years of torrential rains that began in 1315 led to the Great Famine of 1315-1317. The Thames River in London froze over, the growing season was significantly shortened, crops failed repeatedly, and wine production dropped sharply (Fagan, 2000; Singer and Avery, 2007).
Winters during the Little Ice Age were bitterly cold in many parts of the world. Advance of glaciers in the Swiss Alps in the mid–17th century gradually encroached on farms and buried entire villages. The Thames River and canals and rivers of the Netherlands frequently froze over during the winter. New York Harbor froze in the winter of 1780 and people could walk from Manhattan to Staten Island. Sea ice surrounding Iceland extended for miles in every direction, closing many harbors. The population of Iceland decreased by half and the Viking colonies in Greenland died out in the 1400s because they could no longer grow enough food there. In parts of China, warm weather crops that had been grown for centuries were abandoned. In North America, early European settlers experienced exceptionally severe winters.
Temperature changes recorded in the GISP2 ice core from the Greenland Ice Sheet show that the magnitude of global warming experienced during the past century is insignificant compared to the magnitude of the profound natural climate reversals over the past 25,000 years, which preceded any significant rise of atmospheric CO2. If so many much more intense periods of warming occurred naturally in the past without increase in CO2, why should the mere coincidence of a small period of low magnitude warming this century be blamed on CO2?