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A Reexamination of Climate Change Issues

Famine and Drought Associated with Global Warming

 updated November 29, 2009

Much of the American West has been much dryer during periods over the past few thousand years than it has been during the past century.
Much of the American West has been much dryer during periods over the past few thousand years than it has been during the past century.

Historically, human food production has increased and flourished during periods of global warming, such as during the Medieval Warm Period between the years 800 and 1300 AD. However, studies show that a warming climate would bring an increased risk of drought in certain regions of the world including California, Mexico, and southern Africa, although the climate shifts would happen very gradually, giving time for populations to adapt with improved farming technology. Droughts are also shown in occur in periods of global cooling.



Following are excerpts from the book ”Unstoppable Global Warming— Every 1,500 Years,” which show the realities of drought associated with climate change:

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Human food production historically has increased during periods of global warming. Earlier chapters documented conclusively that human society flourished during the Roman and Medieval Warmings.

Food production increased during pervious warmings primarily because warming climates provided more of the things plants love: sunlight, rainfall, and longer growing seasons. During warmings there is also less of the things plants hate: late spring and early fall frosts that shorten the growing season, and hailstorms that destroy fields of crops.

History tells us the both warming and cooling may trigger very long droughts in some regions. The increased temperatures of the Modern Warming may have some negative impact on crops in the southern mid-latitudes--through drier summers, for example--in places such as southern Romania, Spain, and Texas. There is reason to believe that California, Mexico, and southern Africa all run increased drought risks as the 1,500-year climate cycle continues its solar-driven course.

Extended droughts cause damage whenever and wherever they occur. However, our information from fossils, tree rings--and climate models--on where and when such droughts might occur is fragmentary and uncertain. We don’t know yet where our descendants will need additional flood control or water storage--let alone the technologies they will have to provide them.

Fortunately, a natural warming will move along a slowly erratic course over the coming centuries, giving time for the farmers, communities, and governments to adapt. These adaptations are likely to come gradually, in modest increments, as public opinion and technical feasibility determine what changes need to be made.

The geologic record indicates that the whole western part of the United States has normally been drier in earlier periods than during the 20th century. The water wells dug by the Indians in the High Plains 6,000 years ago indicate a drought that lasted 2,500 years, leaving the Great American Desert in its wake. (395) That was during the very warm (Holocene) Climate Optimum when summer temperatures were 2 to 4 degrees C higher and precipitation was lower than today. (396) [ See this study and this study ]

Additional evidence of higher temperatures and more dryness comes from annual layers of lake sediment from Elk Lake, Minnesota, (397) and Chappice Lake, Alberta. (398) Both sets of lake sediments indicate a prairie landscape that peaked in warmth and dryness 7,000 years ago during the Climate Optimum. It was then covered with sparse forage and with only drought-resistant plants and animals. [ See this study and this study ]

High Midwest temperatures and lower rainfall also produced extensive sand dunes across much of the western United States, including the High Plains, Rocky Mountain Basin, parts of the Midwest, Texas, and New Mexico. (399) [ See this study, this study, and this study ]

Explorers on the Great Plains during the 19th century wrote of a landscape full of moving sand dunes and sheets. (400) These written records are endorsed by tree ring evidence from the Great Plains in that period. (410) The mobilization of sand dunes during the last 1,000 years has been small, regional, and intermittent by comparison. (402) The prevalence of lighting-caused prairie fires may also have contributed to the bare earth and resulting sand movements. [ See this study, this study, and this study ]

Droughts are a potential problem during a global warming, but they are also a frequent problem during global cooling. The flood history of the upper Mississippi Valley includes a warm, dry climate from 3000 B.C. to 1300 B.C., with rain and snowfall totaling about 15 percent less than today, according to James C. Knox of the University of Wisconsin. Then precipitation gradually increased to a period of record floods during the Medieval Warming (900 to 1300) and the transition to the Little Ice Age in the early 14th century. (403)

Knox used the flood-deposited cobblestones found in the overbank flood plains to calculate the minimum flood depth needed to transport the stones, along with radiocarbon dating to determine the ages of the flood gravels. He says Mississippi floods during the past 150 years have been relatively small and infrequent, with only three extreme floods (1851, 1973, and 1993). If the current global warming repeats the weather patterns of the very warm Climate Optimum (9000 B.C. to 2000 B.C.), the Mississippi Valley could again have much more frequent big floods.

The National Climate Data Center also says the southwestern United States had long periods of drought over the last 2,000 years, but with frequent, extreme floods during the Climate Optimum. (404) The first two hundred years of the Little Ice Age saw a few large Southwestern floods, but then frequent large floods at the end of that cold era in the 19th century. The Center used tree ring data, confirmed by radiocarbon dating of extreme flood deposits.

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Citations



(395) D.J. Meltzer, ”The Parching of Prehistoric North America,” New Scientist 131 (1991):39-43.

(396) Cooperative Holocene Mapping Project Members, ”Climate Changes of the last 18,000 Years: Observations and Model Simulations,” Science 241 (1988):1043-52.

(397) W.E. Dean et al, ”The Variability of Holocene Climate Change: Evidence from Varved Lake Sediments,” Science 226 (1984):1191-194.

(398) R.E. Vance et al., ”7,000-Year Record of Lake-Level Change on the Northern Great Plains: A High-Resolution Proxy of Past Climate,” Geology 20 (1992):870-82.

(399) S.L. Forman et al., ”Large-Scale Stabilized Dunes on the High Plains of Colorado: Understanding the Landscape Response to Holocene Climates with the Aid of Images from Space,” Geology 20 (1992):145-48; D.R. Muhs and P.B. Maat, ”The Potential Response of Eolian Sands to Greenhouse Warming and Precipitation Reduction on the Great Plains of the U.S.A.,” Journal of Arid Environments 25 (1993):351-61; and W.E. Dean et al., ”Regional Aridity in North America during the Middle Holocene,” The Holocene 6 (1996):145-48.

(400) D.R. Muhs and V.T. Holliday, ”Evidence of Active Dune Sand on the Great Plains in the 19th Century from Accounts of Early Explorers,” Quaternary Research 43 (1995):198-208.

(401) D. Meko et al., ”The Tree-Ring Record of Severe Sustained Drought,” Water Resources Bulletin 31 (1995):789-801; Muhs and Holliday, ”Evidence of Active Dune Sand,” 198.

(402) R.F. Madole, ”Stratigraphic Evidence of Desertification in the West-Central Great Plains within the Past 1,000 Years,” Geology 22 (1994):483-486.

(403) J.C. Knox, ”Climatic Influence on Upper Mississippi Valley Floods,” in Flood Geomorphology, ed. V.R. Baker, R.C. Kochel, and A.C. Patton (New York: Wiley and Sons, 1988), 279-300; J.C. Kochel, and A.C. Patton (New York: Wiley and Sons, 1988), 279-300; J.C. Knox, ”Large Increases in Flood Magnitude in Response to Modest Changes in Climate,” Nature 361 (1993): 430-432.

(404) National Climate Data Center, ”Developing a Tree-Ring Data Bank to Help Answer Questions about Global Change,” 1996 (accessed 8/5/07)











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