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Early Anthropogenic Influence on Climate and the Avoidance of an Ice Age

Blake Earle. Early Anthropogenic Influence on Climate and the Avoidance of an Ice Age. William F. Ruddiman. “How Did Humans First Alter Climate?” from Scientific American, March 2005 Plows, Plagues, and Petroleum: How Humans Took Control of Climate. Ruddiman , 2001. Ruddiman, 2007.

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Early Anthropogenic Influence on Climate and the Avoidance of an Ice Age

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  1. Blake Earle Early Anthropogenic Influence on Climate and the Avoidance of an Ice Age

  2. William F. Ruddiman “How Did Humans First Alter Climate?” from Scientific American, March 2005 Plows, Plagues, and Petroleum: How Humans Took Control of Climate Ruddiman, 2001

  3. Ruddiman, 2007

  4. Ruddiman, 2007

  5. A Short History of CO2 and CH4 • Over the past 400,000 years the Milankovitch Cycles have controlled CO2 and methane concentrations. • Methane fluctuates at the 22,000 year tempo (precession) as the Northern Hemisphere swings closer towards the sun and receives a boost in radiation, leading to greater decomposition of plant matter in wetlands. Ruddiman, 2005

  6. A Short History Continued • In southern Asia increased solar radiation strengthens monsoon cycles that flood areas that would otherwise remain dry. • In far northern Asia and Europe warmer summers thaw boreal wetlands for longer periods. • In both areas this process allows more vegetation to grow, decompose, and emit methane at a predictable 22,000 year tempo. Ruddiman, 2005

  7. Oddities: CH4 Ruddiman, 2007

  8. Oddities: CO2 Ruddiman, 2007

  9. Possible Explanations • Other investigators have suggested the following to explain these oddities: • Expansion of wetlands in Arctic regions • CO2 rise has been attributed to natural losses of vegetation rich in carbon • Changes in ocean chemistry • However, Dr. Ruddiman was not content with these explanations, citing the fact that the parameters for climate change have been the same in all other inter-glacial periods. Ruddiman, 2005

  10. Ruddiman’sExplination MAN

  11. A Short History of Agriculture • Agriculture originated approximately 11,000 years ago in the Fertile Crescent, shortly after in China and several thousand years later in the Americas. • By 2,000 years ago every food crop eaten today was being grown some where in the world. • Various agricultural activity produce both CH4 and CO2 Ruddiman, 2005

  12. A Short History Continued Ruddiman, 2007

  13. Agriculture and Gas Projection • One common practice tied to farming was deforestation which became popular in China and Europe approximately 8,000 years ago. • Fallen trees were either burned or left to rot, both processes emit CO2 to the atmosphere. Ruddiman, 2005

  14. Flashback! Ruddiman, 2007

  15. Agriculture and Gas Projection • Around 5,000 years ago farmer in southern China began to flood lowland areas near rivers in order to propagate wet-adapted strains of rice. • By 3,000 years ago this procedure spread south into Indochina and west towards the Ganges River Valley. • This process is a major produce of methane. Ruddiman, 2005

  16. Flashback!! Ruddiman, 2007

  17. Ice Age? • Stephen J. Vavrus and John E. Kutzbach along with Dr. Ruddiman used a climate model to predict modern-day temperature in the absence of these agriculture related greenhouse gas emissions. • The result showed a difference of two degrees Celsius. • Other researchers have previously shown that parts of northeastern Canada might be covered with ice if world temperature was a mere 1.5 degrees Celsius cooler. Ruddiman, 2005

  18. Ice Age? Ruddiman, 2007

  19. A New Picture Ruddiman, 2007

  20. A Long Story Short “My findings add a new wrinkle to each scenario. If anything, such forecasts of an “impending” ice age were actually understated: new ice sheets should have begun to grow several millennia ago. The ice failed to grow because human-induced global warming actually began far earlier than previously through—well before the industrial era.” ~William F. Ruddiman

  21. Critiques • Some have suggested that the anomaly Ruddiman observed is unfounded because he did not investigated an interglacial 400,000 years ago in which solar radiation trends were more like those of today. • Other doubt Ruddiman’s suggestion that the 40-ppm CO2 anomaly was caused by 200 billion tons of carbon produced by human activity. They have suggested that between 550-700 billion tons of carbon would have been needed, and since humans could not have produced this much carbon in the past few thousand years, humans are not the cause of the anomaly in carbon. Ruddiman, 2007

  22. Sources Ruddiman, William F. Earth’s Climate. New York: W.H. Freeman, 2001. Ruddiman, William F. “How Did Humans First Alter Global Climate?” Scientific American March 2005. Ruddiman, William F. Plows, Plagues, and Petroleum: How Humans Took Control of Climate. Princeton: Princeton UP, 2007. Ruddiman, William F. Orbital insolation, ice volume, and greenhouse gases. http://cfa-www.harvard.edu/~wsoon/Liu03-d/ODP1012-d/Ruddiman03.pdf Ruddiman, William F. Environmental Sciences Department. http://www.evsc.virginia.edu/faculty/people/ruddiman.shtml Earth Observatory Library Milutin Milankovitch. http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/ I couldn’t have done it better myself.

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