A probabilistic quantification of the anthropogenic component...

Discussion in 'Environment' started by Trakar, Dec 19, 2012.

  1. Trakar
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    Trakar VIP Member

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    A probabilistic quantification of the anthropogenic component of twentieth century global warming

    T. M. L. Wigley • B. D. Santer
    http://link.springer.com/content/pdf/10.1007%2Fs00382-012-1585-8
    Significant excerpts
    “Abstract - This paper examines in detail the statement in the 2007 IPCC Fourth Assessment Report that ‘‘Most of the observed increase in global average temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations’’. We use a quantitative probabilistic analysis to evaluate this IPCC statement, and discuss the value of the statement in the policy context. For forcing by greenhouse gases (GHGs) only, we show that there is a greater than 90 % probability that the expected warming over 1950–2005 is larger than the total amount (not just ‘‘most’’) of the observed warming…
    …In the following, we confirm the IPCC statement regarding the GHG component of anthropogenic warming, and show that this statement is probably too conservative. In addition to the ‘‘GHG only’’ component of warming, we also consider the total effect of all anthropogenic emissions, where GHG warming is partly offset by the cooling effect of sulfate aerosols. Our method for assessing the ‘‘GHG only’’ and ‘‘total anthropogenic’’ components of observed global-mean surface warming produces probabilistic estimates of these components …

    …We first consider results for the 56-year period from 1950 to 2005. The key result here is that for the ‘‘GHG forcing only’’ case (Fig. 4a), which relates directly to the 2007 IPCC statement. Over this interval the observed (NOAA/NCDC) robust trend, with ENSO removed, is 0.610C (see Table 3). The median model robust trend is 0.940C. The probability that the model-estimated GHG component of warming is less than the observed trend is approximately 7 %. Using IPCC terminology, therefore, it is very likely that GHG-induced warming is greater than the total warming observed over this 56-year period (i.e., the model GHG-only trend is not just greater than ‘‘most’’ of the observed warming, but very likely greater than the full amount of observed warming). As noted above, there is ambiguity in the meaning of the word ‘‘most’’ in the IPCC statement that we have focused on here. If ‘‘most’’ means anything more than 50 % (i.e., for NOAA/NCDC data, a warming greater than about half of 0.610C = 0.305C), then the IPCC statement is far too conservative. For GHG forcing alone, the lowest warming value over 1950–2005, in all of the 625 cases considered (25 sensitivities and 25 diffusivities), is 0.469C, much greater than 0.305C. If, however, ‘‘most’’ means almost all, then our result is entirely consistent with the IPCC statement and provides strong support for this statement.

    Results for the ‘‘all anthropogenic forcing’’ case (Fig. 4b) are of equal interest, and provide information on the overall consistency between the model-predicted changes and observations. When one accounts for both positive (GHG) and negative (net aerosol) forcings, the median model expectation for the net warming over 1950–2005 (0.557C) is very similar to the observed warming (0.610C) In the 19,375 simulations the model predicted warming is smaller than the observed warming in 61 % of the cases and larger than the observed warming in 39 % of the cases. This result is relatively insensitive to the inclusion of the effects of natural solar and volcanic forcing (see next section)…

    … For trends over 1950–2005, when one accounts for both greenhouse gas and aerosol forcings, the model expectation for the net warming is consistent with the observations. Including the effects of solar and volcanic forcings slightly reduces the median warming (see Fig. 6), but does not lead to a statistically significant difference between the median model expectation and any of the observed warming trends. Overall, our results provide strong confirmation of the IPCC findings, and are in close agreement with pattern based fingerprint analyses, such as those of Stott et al.(2006).”

    Very impressive and rigorous analyses amounting to what most consider compelling support.

     
  2. IanC
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    IanC Gold Member

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    some of us dont find computer model simulations to be compelling. especially when they consistently predict warmer temperatures than reality provides.

    Santer is very prone to casting about, looking for spurious coincidences, to find 'evidence' for his preformed conclusions.
     
  3. Trakar
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    Trakar VIP Member

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    I understand that those who dismiss entire regimes of mathematics, statistical analysis and validity modelling (the undepinnings of most modern science and the technologies of the modern world) with a wave of their hand while disparaging noted leaders in these fields without addressing the nature or specifics of their researches, are not ameniable to the consideration of any evidences or arguments that they feel threatens their ideological based preconceptions.

    As the adage affirms, "you can lead a horse to water,..."
     
  4. Old Rocks
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    Old Rocks Diamond Member

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    There are studies going on presently in the fields of paleo-climatology, studies of the physics of glacial ice, of the chemistry and physics of ocean clathrates. All dismissed by people who prefer to think in terms of the Way Things Oughta Be rather than facing the reality that is now upon us.
     
  5. Quantum Windbag
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    Quantum Windbag Gold Member

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    Or, just a thought, we could use real world data instead of computer models.

    Matt Ridley: Cooling Down the Fears of Climate Change - WSJ.com
     
  6. westwall
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    westwall USMB Mod Staff Member Gold Supporting Member Supporting Member

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    Yes, you can. Fortunately, I'm a human, and can actually think for myself and don't need to be forcefed like you all do so here we have a small snippet of your "study". There is a very important sentence in here....can you find it?



    In comparing model and observed temperature changes, the
    key model uncertainties are in the imposed external forcings
    (mainly in the forcing due to aerosols) and the model
    response to these forcings (the ‘‘signal’’). Response uncertainties
    arise primarily through uncertainties in the climate
    sensitivity and uncertainties in ocean heat uptake. In addition,
    in both the real world and in complex coupled Atmosphere/
    Ocean General Circulation Models (AOGCMs), the
    noise of natural internally generated variability introduces
    additional uncertainties in estimates of the climate-response
    signal.
    In this section we compare observed near-surface temperature
    changes with model results for a range of specific
    climate sensitivities (1.5, 3.0 and 6.0 C) and for low, mid
    and high aerosol forcing. We also consider the zero aerosol
    forcing case, corresponding to GHG forcing alone. Ocean
    heat uptake uncertainties are addressed in the next section.
    Since our focus is on the effects of anthropogenic forcing,
    we do not consider natural external forcing factors (solar
    and volcanic) in these initial analyses.
    Our model simulations use a relatively simple climate
    model that facilitates an assessment of uncertainties.
     
  7. Old Rocks
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    Old Rocks Diamond Member

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    A lecture from the 2012 American Geophysical Union Conferance.

    [ame=http://www.youtube.com/watch?feature=player_embedded&v=RICBu_P8JWI]Tyndall Lecture: GC43I. Successful Predictions - YouTube[/ame]
     
  8. bripat9643
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    bripat9643 Diamond Member

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    Anyone who understands the term GIGO (garbage in, garbage out) can easily dismiss computer models for the fiction they are. It has nothing to do with feeling "threatened" by their preconceptions. One bogus "preconception" the global warming cult members all suffer from is the idea that computer models bare some semblance to reality.
     
    Last edited: Dec 20, 2012
  9. Old Rocks
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    Ya, sure, Pattycake. The fact that you haven't the intellect to understand science affect none of the rest of us.
     
  10. IanC
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    IanC Gold Member

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    how odd. the skeptical side keeps using "entire regimes of mathematics, statistical analysis and validity modelling" to show how climate science is incorrect in many areas yet you stand firm in your support of it.

    the Mann hockeystick graph took years to demolish, and many adherents still like to believe that it is 'consistent with' the data even though it has been shown to have no statistical validity. unfortunately it has not been withdrawn, probably because so many later studies used its tainted findings and the logistics of reanalyzing dozens of articles is daunting for the reputations of the journals that published them. fast forward to the present and we find papers like Gergis et al that use better methods and data than the original Mann papers yet it was demolished in days by web review and forced to be withdrawn.

    I follow most of the AGW news, from both sides although it is harder and harder to find decent pro-AGW sites lately. all the areas have been scaled back from the crackpot catastrophic conclusions of ten years ago, with the exception of 'extreme weather' which seems to survive even though the evidence is mostly against it.

    you can lead a man to evidence, but you can't make him think.
     
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