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Anthropocentrism, big impact on climate

  1. Mar 3, 2006 #1
    Let's do another one.

    The idea that humans can and have had a big impact on climate is increasingly thriving. Apparently we are the central factor -Anthropocentrism. It started with Ruddiman who had produced a study His point is that the current Holocene shows an unique rise in carbon dioxide (measured in Antarctic ice cores) from some 255 ppm to 280 ppm. The other end of icing stadial spikes that indicate the start of interglacials show a (sometimes very) slow decline after the intial spike as seen here.

    How come, well the paleolithic man started to change his environment, cutting down forests to build villages, burn fires and have land for agriculture. This would remove the carbon sink function and would increase the CO2 in the air.

    So what do you say about that?
     
  2. jcsd
  3. Mar 3, 2006 #2
    Hi Andre!

    Pretty depressing, eh? As I recall, we agree that deforestation is a "bad thing."

    It sounds like you read the SciAm article (based on the timing of your post.) The original is 3 years old and speaks about rice paddies too.

    What do I think? Either the idea is too far fetched, or it's right - in which case a runaway greenhouse seems inevitable.

    What do you think?
     
  4. Mar 3, 2006 #3

    Mk

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    Why is deforestation bad?
     
  5. Mar 3, 2006 #4
    becomes harder and harder to sequester carbon dioxide, whether the CO2 is produced by man or not. (IOW, the forests-are-good thing is easier to agree on than the source or causative ffect of CO2vs.warming.)

    Well, deforestation also reduces habitat. That may be the basis for me and Andre agreeing that deforestation is bad, assuming that my memory is right and we agree that it's bad.

    Yeah, I know, this is almost unreadable. Flag me if I don't make any sense.
     
    Last edited: Mar 3, 2006
  6. Mar 4, 2006 #5
    Good to see you, Patty. Yes we agree, deforestation is bad for biodiversity, soil preservation, food chains and microclimate and some more. And the reason for the thread was this article (may be the same as the SciAm? another study.

    It argues that the bubonic plague decimated the population in the medieval period reversed the antropogenic deforestation. They see concurent CO2 level changes in leaf stomata

    I had a discusion with the author showing him that his leaf stomata CO2 reconstruction, which correlated positively with ice cores, did not correlate with the more recent multiproxy climate reconstruction known as Moberg 2005 here.. This should put some question marks at that CO2 - global temperature relationship.

    Moreover the period of interest of Ruddiman, the second half of the Holocene, shows similar patterns: rising CO2, lowering temperatures.

    The graph shows the temperature reconstructions based on the Greenland Ice cores (black) and the Antarctic ice cores (grey) versus CO2 (red)

    So CO2 is still not a major climate driver and I have loads of new evidence. But posts should not be too long. Interested?
     
  7. Mar 4, 2006 #6
    No, not particularly, though it's nice to see you as well. (Have you noticed that the conversations on message boards don't really go anywhere?)

    I've enjoyed being less active on the internet and I don't wish to get too into message boards again.

    Nothing personal.
     
  8. Mar 4, 2006 #7
    Well hoping to see you around very occasionally.

    Indeed conversations here are mostly a conflict of interest. Each party's objective being to make a point and being right, rather than a common desire to find the truth.

    It's probably all about the observations of T.C. Chamberlin, (highly recommended to read in full)

    That's why I'm trying to scrutinize everything.

    Therefore, despite the apparant exhaustive dealing with the subject of Anthropogenic Global Warming, I would like to suggest one question whenever the next alarmist message emerges about sealevels glaciers, storms, what have you: "Suppose that the cause of that warming is something else than antrhropogenic greenhouse gas effect?".

    And that something else can be found here: Fortunately a short thread.
     
  9. Mar 4, 2006 #8
    Well, that's easy. Then nothing we do will really matter - unless we identify the non-anthropogenic effect and reverse it somehow.

    But, since we won't reach certainty that it is not anthropogenic (ie there will always be some concern that human activity contributes), it continues to make sense to try to reduce emissions, reduce population load, look at the long term consequences, and continue to try to research the situation.

    We do have a much better understanding of climate than thirty years ago, after all, and that's because science has been trying to understand the factors that contribute to climate.

    (I'm still not here. I mean it.)
     
  10. Mar 5, 2006 #9
    Well I guess that the (huge) albedo changes may or may not have cyclic interaction with ocean surface temperatures and for some reason that cycle is somewhat stronger than the last one in the 1940ies. But that's very tentative.

    We could have a good understanding if it wasn't for the continuous attempt to overestimate the sensitivity to GHG forcing due to positive feedbacks. If there were positive feedbacks life at earth would have ceased to exist long time ago. As the albedo research suggests the feedback -actually gain- may be strongly negative or we're dealing with a gain of less than 0,5. With the psysical measurable (Stefan Boltzman) forcing of 0,7 degrees dynamically initially to 1,2 degrees steady state after some centruries for doubling CO2. The negative feedback would make that less than half. Which suggests that whatever good reasons there are to cutback emisions, climate is not one of them.

    Then, have a good time elsewhere.
     
  11. Mar 5, 2006 #10
    Because plants help take in the carbon dioxide we breath in and turn it into oxygen that we can breath.If hunans > plants that makes the air balance so we have less air to breath.
    The Rain forest helps alot with truning carbon dioxide into oxygen and cutting them down would make things very unblanced.
     
  12. Mar 5, 2006 #11

    Mk

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    How quickly is it going? I remember Thomas Malthus wrote about the population bomb in the 1700s, which could've happened without technology.
     
  13. Mar 5, 2006 #12

    Mk

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    Are they really huge or are you sarcasticizing? :tongue: I never read that paper somebody posted in the global dimming thread. I even saved it too.

    :rofl: Wow you guys civilly really don't like each other.
     
  14. Mar 6, 2006 #13
    Yes they are, seriously, 10-11% is huge:

    http://home.wanadoo.nl/bijkerk/albedo-temp.GIF
    http://home.wanadoo.nl/bijkerk/albedo2.GIF

    which gives Earth blackbody temperature variations of about 3 degrees Kelvin/Celsius, as I said, it dwarfs the greenhouse factor with only a few tenth C at the most.

    No, your perception is wrong. Its just that I'm non native tongue and not very good at subtly conveying emotions. I do wish Patty all the best. :approve: After all, running a family is priority #1.
     
  15. Mar 6, 2006 #14

    Mk

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    Are you approximating Earth to a black body to get its black body temperature?
     
  16. Mar 6, 2006 #15
    Deforestation happens. Landslides, volcanos, fires, infestation, disease and floods. They all kill trees/plants. All these factors have happened long before humans chopped down trees to make paper and houses.
    Did the climate change because of these natural occurances? Yes. Sometimes the climate would change drastically and globally to the point of a volcanically induced nuclear winter.

    However, naturally occuring deforestation happens randomly and usually to the benefit of the environment, spurring new growth with more sunlight and so on. Whereas humans continue to deforest everything in sight, leaving little time for reforestation between clear cuts. I can see how this could push deforestation and the climate a little further than the occassional blight of bugs or volcanic blow out... perhaps all the way to the extinction of those concerned.
     
  17. Mar 6, 2006 #16
    Have a look here

    See expression 5: (sorry Latex not working on this machine)

    G = σTe^4 = (1-A) S / 4

    Te is the blackbody temperature,

    A is albedo, normal 0,3

    S is solar flux

    σ is the Stefan Bolzman constant (5,67 * 10-8)

    Reworked in expression [5] to solve temperature:

    Te = ((1-A) S / 4 σ)^1/4

    Solving this equation with S = 1376.6 and Albedo 0,3 gives a blackbody temp of 254.9K. You can check with google that 255K is indeed quite synonym to black body temperature. So far, so good.

    So what would a 10% variation of albedo give?

    A = 0.27: Te =257,6K (+ 2.7 K)

    and

    A = 0.33: Te = 252.1 (- 2.8 K)

    This would be the average temperature of a rotating (heating and cooling) earth without any secondary thermal effects like GHG or latent heat or heat transport, conduction, etc.

    So if none of those effects would have worked the 10% albedo change of the last decade should have given an average global temperature change of 2.8K

    But it was only 0.5 - 0.6 K.

    Now you can model whatever you like but reducing such a enormouos insolation difference by a about a factor 5 (or 20% feedback) would suggest a very strong negative feedback from al the thermal processes. The same strong negative feedback could nullify changes in greenhouse effect.
     
  18. Mar 6, 2006 #17
    Anthropogenic deforestation is a big problem but there are positive sounds. In Africa there is a single woman fighting it, succesfully. She won the nobel price for peace. Meet Wangari Maathai and have deep respect for such an accomplishment.
     
  19. Mar 6, 2006 #18
    I don't know what exactly you are getting at - so I hope I am not taking you out of context here:

    You can't conclude that the existence of positive feedbacks precludes life from continuing.

    For one thing, some cycles (eccentricity of orbit, wobble of the earth, etc) would change the amount of energy coming into the system - Those cycles could offset a positive feedback loop.

    For another thing, the presence of one positive feedback doesn't mean that other types of feedback aren't also at work. For example, the snowball earth idea was a positive feedback cooling trend and most life stopped. But volcanism eventually allowed enough gasses to accumulate to escape the snowball. Thus, as one feedback changes the climate, other factors - in this case the accumulating emission of CO2 from volcanoes with no plants to absorb it - can tip the planet back.

    For a third thing, there have been mass extinctions - perhaps due in some part to "positive-feedback" climate - and at least the ediacaran extinction seemed to be pretty absolute. Yet, microorganisms tend to survive those sorts of events because they are so genetically resilient. And life resumes.


    -Patty

    (Aside to MK: I chuckled at your "civil dislike" comment. It reminds me of the Cheers episode where Sam is with a girl in a hotel, "before," and he is folding his socks, because "he's not an animal, after all.")
     
  20. Mar 6, 2006 #19
    Patty,

    I think the wording "positive feedback" is not correct, in a linear closed loop system, positive feedback means per definition instability where any displacement from the normal value means an accelerated increase of that displacement, which is not stopping until the system crashes. The nightmare for the physical system designers. What is meant here is non-linear feedback and system gain.

    About Snowball earth, remember the philosophy of TC Chamberlain about hasty conclusions and sticking to it. So some researchers find glacial stratifications on the apparent paleao equator and bingo we have snowball Earth. Later research has shown though that normal oceanic benthic activity has prevailed throughout the period, suggesting that the oceans were just open, business as usual. it is suggested that this period looked a lot like the modern times with occasional increases of polar ice sheets.The snowball earth has melted.

    Yes, there have been large mass extinctions indeed, seven now I believe, two more have been identified. The causes are moderately ambiguous. There are several catastrophic occurrences associated with most events, remarkable are several combinations of bolide impacts (large meteorites) followed by antipode basaltic flood volcanism. Most intriguing study here:

    http://www.mantleplumes.org/WebDocuments/Antip_hot.pdf
     
    Last edited: Mar 6, 2006
  21. Mar 7, 2006 #20

    Mk

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    How did she win the Nobel peace prize? I thought they gave it to more deserving people. Cutting down trees does not really constitute much violence to me, and there is no genocide she stopped.
     
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