Magnitude and Range of Climate Change

by Dr. Don J. Easterbrook
January 26, 2011

Continues from page 1

The Little Ice Age (1300 A.D. to the 20th century)

At the end of the Medieval Warm Period, ~1230 A.D., 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.


If CO2 is indeed the cause of global warming, then global temperatures should mirror the rise in CO2. For the past 1000 years, atmospheric CO2 levels remained fairly constant at about 280 ppm (parts per million). Atmospheric CO2 concentrations began to rise during the industrial revolution early in the 20th century but did not exceed about 300 ppm. The climatic warming that occurred between about 1915 and 1945 was not accompanied by significant rise in CO2. In 1945, CO2 emission began to rise sharply and by 1980 atmospheric CO2 had risen to just under 340 ppm. During this time, however, global temperatures fell about 0.9°F (0.5° C) in the Northern Hemisphere and about 0.4°F (0.2° C) globally.

Global temperatures suddenly reversed during the Great Climate Shift of 1977 when the Pacific Ocean switched from its cool mode to its warm mode with no change in the rate of CO2 increase. The 1977–1998 warm cycle ended in 1999 and a new cool cycle began. If CO2 is the cause of global warming, why did temperatures rise for 30 years (1915-1945) with no significant increase in CO2? Why did temperatures fall for 30 years (1945-1977) while CO2 was sharply accelerating? Logic dictates that this anomalous cooling cycle during accelerating CO2 levels must mean either (1) rising CO2 is not the cause of global warming or (2) some process other than rising CO2 is capable of strongly overriding its effect on global atmospheric warming.

Temperature patterns since the Little Ice Age (~1300 to 1860 A.D.) show a very similar pattern; 25–30 year–long periods of alternating warm and cool temperatures during overall warming from the Little Ice Age low. These temperature fluctuations took place well before any significant effect of anthropogenic atmospheric CO2.


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?

Cuffey, K.M. and G.D. Clow, 1997, Temperature, accumulation and ice sheet elevation in central Greenland through the last deglacial transition: Journal of Geophysical Research, vol. 102, p.26383-396.
Fagan, B., 2007, The Little Ice Age: Basic Books, NY, 246 p.
Fagan, B., 2008, The great warming: Bloomsberg Press, NY, 282 p.
Grove, J.M., 2004, Little Ice Ages: Ancient and modern: 2nd edition, vol. 1,2, 718 p.
Oliver, J.E., 1973, Climate and man’s environment: Wiley, NY, 365 p.
Singer, S.F., and Avery, D.T., 2007, Unstoppable global warming: Rowman and Littlefield, 278 p.
Stuiver, M. and Grootes, P.M., 2000, GISP2 oxygen isotope ratios: Quaternary Research, vol. 53, p. 277–284.

Dr. Don J. Easterbrook is Emeritus Professor of Geology at Western Washington University where he has conducted research on global climate change in western North America, New Zealand, Argentina, and various other parts of the world for the past 48 years. He has written three textbooks and several other books, about 150 papers in professional journals, and has presented 30 research papers at international meetings in 12 countries. All of his research has been funded by the National Science Foundation and other U.S. government agencies.

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