4.23 How Much Carbon Dioxide is Man Made?
Charles David Keeling called Dave by his friends, is famous for being a pioneer in carbon dioxide measurements of the atmosphere. He started out in graduate school studying polymer chemistry and probably would never have made carbon dioxide measurements if it was not for his love of the great outdoors, especially the great outdoors in the western United States.. Daniel Harris wrote about him as follows:
"One day, he noticed the book Glacial Geology and the Pleistocene Epoch on a friend’s bookshelf. Keeling became so interested in the book that he bought a copy, read it between experiments in the lab, and imagined himself “climbing mountains while measuring the physical properties of glaciers.” In graduate school, he completed most of the undergraduate geology curriculum. Twice he went hiking and climbing in the Cascade Mountains of Washington State and once joined a canoe trip in Canada during which he met his future wife, Louise. Upon graduation in 1953, Keeling had job offers from chemical companies in the blossoming plastics industry in the eastern U.S., but he “had trouble seeing the future this way.” Though his graduate adviser considered it “foolhardy” to turn down good jobs, Keeling wrote letters offering his “services as a Ph.D. chemist exclusively to geology departments west of the...continental divide.” He soon became the first postdoctoral fellow with Harrison Brown in the new Department of Geochemistry at Caltech. One of the projects Keeling worked on involved measuring carbon dioxide in the air, in water and in limestone and determining the relationship between the three.
In the following video Dave Keeling's son, Ralph Keeling explains how scientists measure carbon dioxide in the air.
There was a large variation in the measurements he made that might have resulted from industry and cars producing carbon dioxide. It's hard to draw scientific conclusions when measured values are all over the place. A lot of people might have given up at that point but instead he looked for a place far away from industry. He chose to make his measurements at Big Sur which is a beautiful hilly area by the Pacific ocean."
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David Keeling decided to take carbon dioxide measurements at Big Sur every few hours to track any variation. He found that the air had more carbon dioxide at night than during the day. One reason for that may be because plants convert carbon dioxide to oxygen when there is sunlight. He measured carbon dioxide on the top of the Mauna Loa volcano in Hawaii and its value varied during the year. He found that the following year the value varied in the same way. Carbon dioxide levels were higher before plants put on leaves. The diagram below is a plot over the years of carbon dioxide in the air and is called the Keeling curve.
It is possible to determine what the levels of carbon dioxide were in the atmosphere before 1950 by drilling in the Antartica for ice. Microscopic air bubbles trapped in the ice retain CO2 from the time they were formed. If a section of frozen ice core is crushed under vacuum, CO2 is released and can be measured. Here is a graph of carbon dioxide levels from ice cores dating from as far back as 800,000 years ago with the Keeling curve for the years 1950 to 2010 appended at the end.
The beginning of the Industrial Revolution, 1760 is about the time that people started to use machines to make what they had made by hand previously. Those machines were powered by coal and eventually by petroleum, gas, gasoline and other energy sources. Since then the level of carbon dioxide in the atmosphere has increased. The increases and decreases in carbon dioxide in the atmosphere before the industrial revolution are believed be due mostly to changes in the earths temperature over time. The hotter the earth is the less carbon dioxide dissolves in the ocean and the more is released into the atmosphere. Cyclic changes in temperature are thought to arise from periodic changes in Earth’s orbit and the tilt of Earth’s axis.
Carbon 14 is a form of carbon created in the stratosphere by the bombardment of carbon dioxide by neutrons in cosmic rays from outer space. Those cosmic rays are mostly blocked from reaching the surface of the earth by the earth's magnetic field and by the earths atmosphere. Carbon 14 decays to Nitrogen 14 with a half life of 5,730 years. That means half the carbon will be gone in that time. Fossil fuels were formed from ancient plants and organisms about 300 million years ago which is before the age of dinosaurs. The vast majority of Carbon 14 that was in fossil fuels decayed away a long time ago and so fossil fuels have no detectable C14. When we burn fossil fuels and produce carbon dioxide from them the percent of Carbon 14 in the atmospheric carbon dioxide should go down. Three scientists, Kenneth Skrable, George Chabot and Clayton French examined the Carbon 14 data and calculated how much carbon dioxide in the atmosphere is a result of the burning of fossil fuels. They wrote:
"Our results show that the percentage of the total CO2 due to the use of fossil fuels from 1750 to 2018 increased from 0% in 1750 to 12% in 2018, much too low to be the cause of global warming."
There is a problem with this study. The highest carbon dioxide ever got in the last 800,000 years before modern times was about 200 ppm. We can see that from the second graph on this web page. In 2018 according to the graph it rose to about 380 ppm. If the increase was only 12% than it should have increased from 200 ppm to 224 ppm. (12% of 200 is 224) Where dis the other 156% increase in carbon dioxide come from? The authors of the paper argue that the extra carbon dioxide came from the oceans as the oceans heated due to changes in the earths orbit. That would mean the earth is hotter than it has been in the last 800,000 years. The authors say this heating cannot be due to burning of fossil fuels. If so why is the earth hotter than it has been for the last 800,000 years?
I did not realize this problem before I created this lesson. However the lesson is still worthwhile even if it just shows that there can be problems with scientific studies. Maybe this study is clueing us into a mystery that is worth investigating. In addition the background information about Keeling and his discovery that carbon dioxide is increasing is something we should all know about.
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Over the Last 800,000 years carbon dioxide has increased and decreased as the earth has gone from ice age to warmth and back again. Could we be heading for another ice age?