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Some of the answers to the complexities of the climate system are given in my recently published book "ClimateChange: A Realistic Perspective".
Below are extracts from pages 208-213.
The Dust Bowl as described in Wikipedia was a period of severe dust storms that greatly damaged the ecology and agriculture of the American and Canadian prairies during the 1930s; severe drought and a failure to apply dryland farming methods to prevent wind erosion caused the phenomenon. The low rainfalls and very high temperatures in many areas during the 1930’s are unprecedented in modern times. The decade of the 1930s tends to get lumped into a decade of persistent heat and drought, yet, much of the reputation of that decade comes from just two of those years, 1934 and 1936. The summer of 1934 was the culmination of several previous dry summers. 1928 was an exceptionally wet summer for the state, it currently ranks as the 2nd wettest summer on record with a statewide average precipitation of 13.14 inches. Yet, the proverbial faucet was abruptly shut off after that warm season. The summer of 1929 was the exact opposite of the previous summer. Dry conditions continued in 1930, 1931, 1932 and 1933 but those years were not as severe as those recorded in 1929.
By the end of 1935, many farmers, especially in North Dakota thought the dryness that plagued the state was coming to a close, but little did individuals realize that the most extreme year that they would ever experience was about to impact much of the north central United States. The year 1936 started with the most severe cold wave on record. From the middle of January through the middle of February, most of North Dakota did not record a high temperature above 0°F. In fact, Langdon recorded 42 consecutive days during that time frame without the temperature exceeding 0°F. That winter of 1935-1936 was the coldest on record for all of North Dakota and much of the rest of the immediate area. It was toward the end of that horrific cold snap that the coldest observed temperature in North Dakota was recorded. On Saturday, February 15, 1936, cooperative observer Court Shubert recorded a temperature of -60°F. Bismarck reached -42°F that morning, just 3°F shy of the all-time lowest temperature for that location.
NASA scientists have an explanation for one of the worst climatic events in the history of the United States, the “Dust Bowl” drought, which devastated the Great Plains and all but dried up an already depressed American economy in the 1930’s. Siegfried Schubert of NASA’s Goddard Lessons from history 209 Space Flight Center, Greenbelt, Md., and colleagues used a computer model developed with modern-era satellite data to look at the climate over the past 100 years. The study found cooler than normal tropical Pacific Ocean surface temperatures combined with warmer tropical Atlantic Ocean temperatures to create conditions in the atmosphere that turned America’s breadbasket into a dust bowl from 1931 to 1939. These changes in sea surface temperatures created shifts in the large-scale weather patterns and low level winds that reduced the normal supply of moisture from the Gulf of Mexico and inhibited rainfall throughout the Great Plains.
“The 1930s drought was the major climatic event in the nation’s history,” Schubert said. “Just beginning to understand what occurred is really critical to understanding future droughts and the links to global climate change issues we’re experiencing today.” By discovering the causes behind U.S. droughts, especially severe episodes like the Plains’ dry spell, scientists may recognize and possibly foresee future patterns that could create similar conditions. For example, La Niñas are marked by cooler than normal tropical Pacific Ocean surface water temperatures, which impact weather globally, and also create dry conditions over the Great Plains.
Dust storms on the Great Plains
The model showed cooler than normal tropical Pacific Ocean temperatures and warmer than normal tropical Atlantic Ocean temperatures contributed to a weakened low-level jet stream and changed its course. The jet stream, a ribbon of fast moving air near the Earth’s surface, normally flows westward over the Gulf of Mexico and then turns northward pulling up moisture and dumping rain onto the Great Plains. As the low level jet stream weakened, it travelled farther south than normal. The Great Plains dried up and dust storms formed. The research shed light on how tropical sea surface temperatures can have a remote response and control over weather and climate. It also confirmed droughts can become localized based on soil moisture levels, especially during summer. When rain is scarce and soil dries, there is less evaporation, which leads to even less precipitation, creating a feedback process that reinforces lack of rainfall.
The study also shed light on droughts throughout the 20th century. Analysis of other major U.S. droughts of the 1900s suggests a cool tropical Pacific was a common factor. Schubert said simulating major events like the 1930s drought provides an excellent test for computer models. While the study finds no indication of a similar Great Plains drought in the near future, it is vital to continue studies relating to climate change. NASA’s current and planned suite of satellite sensors is uniquely poised to answer related climate questions. (see “On the Cause of the 1930s Dust Bowl,” recently published by Siegfried D. Schubert, Max J. Suarez, Philip J. Pegion, Randal D. Koster, and Julio T. Bacmeister in the March 19, 2004 edition of Science Magazine).
Homestead on the range
The website homestead on the range.com raises the question of the effect of solar cycles. Solar cycles have been observed since 1755, and many scientists have suggested that there is a correlation between the two phenomena. But in relation to the causes of the Dust Bowl the jury is divided. Suffice to say that the Dust Bowl began around 1930 or 1931, depending on where you lived, and ended between 1936 and 1940. The solar minimum (period of least solar activity) occurred in 1933, while the solar maximum (period of most solar activity) appears to have been around 1936 or 1937. The Dust Bowl therefore began as solar activity approached a low and ended about the time solar activity reached a peak (making allowance for regional variation). Some scientists consider that during periods of low solar activity, aerosol particles build up in the earth’s atmosphere, instead of being dispersed by solar ejections. These particles in turn become condensation nuclei for clouds. In contrast clouds with large numbers of condensation nuclei tend to produce less precipitation.
History.com has written comprehensively about the Dust Bowl, as the following extracts show.
The Homestead Act of 1862, which provided settlers with 160 acres of public land, was followed by the Kinkaid Act of 1904 and the Enlarged Homestead Act of 1909. These acts led to a massive influx of new and inexperienced farmers across the Great Plains. Many of these late nineteenth and early twentieth century settlers lived by the superstition “rain follows the plough.” Emigrants, land speculators, politicians and even some scientists believed that homesteading and agriculture would permanently affect the climate of the semi-arid Great Plains region, making it more conducive to farming.
This false belief was linked to “Manifest Destiny”–an attitude that Americans had a sacred duty to expand west. A series of wet years during the period created further misunderstanding of the region’s ecology and led to the intensive cultivation of increasingly marginal lands that couldn’t be reached by irrigation. Rising wheat prices in the 1910s and 1920s, and increased demand for wheat from Europe during World War I encouraged farmers to plough up millions of hectares of native grassland to plant wheat, corn and other row crops. But as the United States entered the Great Depression, wheat prices plummeted. Farmers tore up even more grassland in an attempt to harvest a bumper crop and break even. Crops began to fail with the onset of drought in 1931, exposing the bare, over-ploughed farmland. Without deep-rooted prairie grasses to hold the soil in place, it began to blow away. Eroding soil led to massive dust storms and economic devastation – especially in the Southern Plains.
During the Dust Bowl period, severe dust storms, often called “black blizzards” swept the Great Plains. Some of these carried Great Plains topsoil as far East as Washington, D.C. and New York City, and coated ships in the Atlantic Ocean with dust. Billowing clouds of dust would darken the sky, sometimes for days at a time. In many places, the dust drifted like snow and residents had to clear it with shovels. Dust worked its way through the cracks of even well-sealed homes, leaving a coating on food, skin and furniture.
President Franklin D. Roosevelt established a number of measures to help alleviate the plight of poor and displaced farmers. He also addressed the environmental degradation that had led to the Dust Bowl in the first place. Congress established the Soil Erosion Service and the Prairie States Forestry Project in 1935. These programmes put local farmers to work planting trees as windbreaks on farms across the Great Plains. The Soil Erosion Service, now called the Natural Resources Conservation Service (NRCS) implemented new farming techniques to combat the problem of soil erosion.
The Okies
Roughly 2.5 million people left the Dust Bowl states – Texas, New Mexico, Colorado, Nebraska, Kansas and Oklahoma – during the 1930s. It was the largest migration in American history. Oklahoma alone lost 440,000 people to migration. Many of them, poverty-stricken, travelled west looking for work. From 1935 to 1940, roughly 250,000 Oklahoma migrants moved to California. A third settled in the state’s agriculturally rich San Joaquin Valley. These Dust Bowl refugees were called “Okies.” Okies faced discrimination, menial labour and pitiable wages upon reaching California. Many of them lived in shantytowns and tents along irrigation ditches. “Okie” soon became a term of disdain used to refer to any poor Dust Bowl migrant, regardless of their state of origin. The abandonment of homesteads and financial ruin resulting from catastrophic topsoil loss led to widespread hunger and poverty.
Historian James N. Gregory examined Census Bureau statistics and other records to learn more about the migrants. Based on a 1939 survey of occupation by the Bureau of Agricultural Economics of about 116,000 families who arrived in California in the 1930s, he learned that only 43% of south westerners were doing farm work immediately before they migrated. The poor economy displaced more than just farmers as refugees to California; many teachers, lawyers, and small business owners moved west with their families during this time. After the Great Depression ended, some moved back to their original states. But many others remained where they had resettled and about one-eighth of California’s population is of Okie heritage.
The Dust Bowl as described in Wikipedia says that with insufficient understanding of the ecology of the plains, farmers had conducted extensive deep ploughing of the virgin topsoil of the Great Plains during the previous decade; this had displaced the native, deep-rooted grasses that normally trapped soil and moisture even during periods of drought and high winds. The rapid mechanization of farm equipment, especially small gasoline tractors, and widespread use of the combine harvester contributed to farmers’ decisions to convert arid grassland (much of which received no more than 250 mm of precipitation per year) to cultivated cropland. During the drought of the 1930s, the unanchored soil turned to dust, which the prevailing winds blew away in huge clouds that sometimes blackened the sky.
Black blizzards
These choking billows of dust – named “black blizzards” or “black rollers” – travelled cross country, reaching as far as the East Coast and striking such cities as New York City and Washington, D.C. On the plains, they often reduced visibility to 1 meter or less. Associated Press reporter Robert E. Geiger happened to be in Boise City, Oklahoma, to witness the “Black Sunday” black blizzards of April 14, 1935; Edward Stanley, the Kansas City news editor of the Associated Press, coined the term “Dust Bowl” while rewriting Geiger’s news story.
Patrick Allitt recounts how fellow historian Donald Worster responded to his return visit to the Dust Bowl in the mid-1970s when he revisited some of the worst afflicted counties: Capital-intensive agribusiness had transformed the scene; deep wells into the aquifer, intensive irrigation, the use of artificial pesticides and fertilizers, and giant harvesters were creating immense crops year after year whether it rained or not. According to the farmers he interviewed, technology had provided the perfect answer to old troubles, such that the bad days would not return. In Worster’s view, by contrast, the scene demonstrated that America’s capitalist high-tech farmers had learned nothing. They were continuing to work in an unsustainable way, devoting far cheaper subsidized energy to growing food than the energy could give back to its ultimate consumers. In contrast with Worster’s pessimism, historian Mathew Bonnifield argued that the long-term significance of the Dust Bowl was “the triumph of the human spirit in its capacity to endure and overcome hardships and reverses.”
The Dust Bowl also captured the imagination of the nation’s artists, photographers, musicians, and authors. John Steinbeck memorialised the plight of the Okies in his 1939 novel The Grapes of Wrath. Photographer Dorothea Lange captured what have become classic images of the dust storms and migrant families. Among her most well-known photographs is Destitute Pea Pickers in California. Mother of Seven Children, which depicted a gaunt-looking woman, Florence Owens Thompson, holding three of her children. This picture expressed the struggles of people caught by the Dust Bowl and raised awareness in other parts of the country of its reach and human cost. Artist Alexander Hogue painted Dust Bowl landscapes, and Folk musician Woody Guthrie’s semi-autobiographical first album Dust Bowl Ballads in 1940, told stories of economic hardship faced by Okies in California.
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For further information on a range of weather and climate matters see my recent book "Climate Change: A Realistic Perspective.. The fall of the weather dice and the butterfly effect" . Available from Amazon.au.
