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Did AGW Start Thousands of Years Ago?

  1. Jan 15, 2009 #1
    This hypothesis was put forward some years ago Bill Ruddiman 2003 report. It's an interesting idea. Is this the reason why we're not currently in the early stage of advancing ice sheets?
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  3. Jan 15, 2009 #2


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    My impression is Yes!

    People tend to think of global warming in a very negative sense. However, as Ruddiman shows there is a good side too. Normally, greenhouse gases fall following interglacials as he shows in Figure 2. So, if nature had taken its course, CO2 levels might be only 240ppm. That is they should have gradually fallen from 265ppm instead of rising slowing for 6000 years.

    If greenhouse gases fell as they did following the during the previous interglacial, the world would be much cooler than it is now. With perihelion occuring in January, summers are much cooler and the glaciers would be growing all over the Northern Hemisphere. A broad region of the Canadian interior would have been subject to glaciation for the last several thousand years. It might only be a few hundred feet high, but that's enough to affect weather patterns as well as stop forest growth.

    Remember, the Laurentide ice sheet was huge. It started in Canada, but eventually reached as far south as New York City. If we currently had a large part of Quebec and Ontario (around the Hudson Bay) in the beginning stages of a glacier, it would also have devastating impacts for thousands of mile.

    By the way, CO2 levels fell briefly between 1550 up to the start of the industrial revolution around 1750 and no surprise, that period of time is referred to as the little ice age.
  4. Jan 15, 2009 #3


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    Here is an excerpt from Ruddimen with some emphasis from myself:

  5. Jan 15, 2009 #4

    jim mcnamara

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    FWIW -

    The little ice age is usually cited as starting in 1315 with several years of cold rains that ensued, followed by the Great Famine of 1317. Caused by crop failures from late frosts and fungal infestations of crop plants because of cooler rainier conditions.

    Historical - see Tuchman, Barbara 1978 'A Distant Mirror' for accounts written by contemporary writers.

    In reality the whole 'start' is fuzzy time-wise, depending on what you use to measure it. The start of bad times in Europe is quite distinct in terms of the human condition. Other 'measurables' are things like pack ice increases beginning in 1250 AD. I vote for the human condition as recorded by living people from large areas of Europe.
  6. Jan 15, 2009 #5


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    Here is a commentary that might be of interest:
    Commentary on "The anthropogenic greenhouse era began thousands of years ago". Crusifix et al. Climate Change (2005).
  7. Jan 16, 2009 #6
    Xnn, I totally agree with you on this one.

    The report sounds like it has used climate models without the use of common sense or intuition. A pet hate of mine.
  8. Jan 17, 2009 #7
    It may also be interesting to take note of the official IPCC position:

  9. Jan 17, 2009 #8


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    Good find Andre;

    In other words, they should have compared the current interglacial to the interglacial between 399 - 427 Ka. However, notice the IPCCs following comment:
    In other words, that interglacial had low orbital eccentricity and I am guessing that our current interglacial has moderately low eccentricity. So, maybe our current interglacial has a stronger orbital forcing than the previous 3.

    However, 13C/12C ratios in ice core have not exactly provided good estimates of atmospheric changes because of technical problems. So, it is odd that they suggest that 13C/12C ratios in ice cores need to agree. I look at it that there is still room for more reseach!

    Anyhow, I agree that the early Anthropocene hypothesis needs more work. However, I don't think it is totally dead.

    Let the grant request begin!!!
  10. Jan 18, 2009 #9
    I totally agree again Xnn. Well said about the extraordinary low eccentricity of 399-427 ka, see the graph provided. The data are from Berger and Loutre (1991).

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