Newest IPCC assessment: Increased certainty on AGW

Discussion in 'Too Hot for Swamp Gas' started by Row6, Aug 20, 2013.

  1. GatorRade
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    GatorRade Well-Known Member

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    Climate scientists have identified several factors that influence the climate. Here is an explanation that I've posted for you before from the IPCC describing three basic ways to alter earth's radiation balance: (1) changes in solar inputs, (2) changes in reflection of solar radiation (i.e. albedo), and (3) changes in long-wave radiation coming from earth. And then they recognize feedback mechanisms play an additional role.

    [​IMG]

    The changes that you are asking about (e.g. volcanoes, sea ice extent, desertification, etc) must influence these factors to alter the radiation balance.
  2. OaktownGator
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    OaktownGator Well-Known Member

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    When they say they have "low understanding" (their words) of solar forcing, their confidence levels should reflect that. IMO.

    The last solar cycle appeared to start divergence from the IPCC 95 projections, which had already been adjusted down from the 1990 projections. We went from temperatures that were right on target, to temperatures that the very bottom of their range of projections.

    Certainly we get dips and peaks, so that may not mean anything. But if that divergence continues through this solar cycle and we dip outside of their range of projections, IPCC is going to have to rethink their models for sure. And I would think that gaining a better understanding of solar forcing would be at the top of their list.

    Or maybe they'll just find more aerosols. Who knows? :joecool:
  3. GatorRade
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    GatorRade Well-Known Member

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    Here is one of the sentences from jdr's IPCC link:

    Indeed, they are admitting a low understanding of solar inputs, which does make on one wonder exactly what they mean and how they decided to treat this uncertainty. I wonder if the "long time scales" are the a key to this? The IPCC projections usually only go a few decades into the future. Is it possible that the long term solar variation just isn't relevant on these small time scales?
  4. OaktownGator
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    OaktownGator Well-Known Member

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    Certainly possible. But how about short term variations... the Little Ice Age has to be described as a short term variation, right?
  5. asuragator
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    asuragator Well-Known Member

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    Or maybe they'll find with high confidence what they now have with low confidence. :)

    Actually I don't think the confidence level necessarily has to reflect it because the solar measures used are arguably quite precise. Yet because bivariate correlation between the sun and temperatures disappear in multivariate climate models model when human factors are included, to me suggests pretty strong evidence that even with a low understanding of solar irradiance, it is not a significant factor.

    On the other hand, there are multiple measures of solar effects, so it's possible given the low understanding, scientists have yet to discover ones which might be having a significant effect on current warming trends. I tend not to believe this is the case but it is clearly possible.
  6. GatorRade
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    GatorRade Well-Known Member

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    Good question. I wonder how much we know about the cause of the little ice age? Looks like we have a Nature paper that seems to directly link the Maunder Minimum to the ice age. Therefore, I wonder if (1) 400 years isn't considered "long term" (maybe 10,000 years?) or (2) the IPCC is claiming that they don't understand how to predict another Maunder minimum, as you are suggesting?

    Skeptical science offers a few articles from the literature that suggests that perhaps we don't know how to predict this variation, but that these sunspots don't much matter. Feulner and Rahmstorf 2010 estimates an extremely small effect:

    [​IMG]

    Jones et al. 2012 indicates a very likely small effect as well, but leaves the door open for other possiblities:

    Anet et al. 2013 also gives us a small estimation:

    And Meehl et al. 2013 thinks the same:

    Now it seems to me that while IPCC is admitting that they can't predict a solar minimum, the warming shouldn't be affected in a meaningful way. If this is true, I think their choice to ignore possible sunspot effects is justified. Now of course there is always the chance that the these different effects models are persistently inaccurate in the same direction, but as I understand it, your critique was based on modeled solar input predictions, rather than modeled effects.
  7. asuragator
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    asuragator Well-Known Member

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    I just touched on this to my reply to Oaktown. It reads to me like they are referring to the lack of direct measurement going far back in time, since we have direct measurements in more recent time periods.

    Uncertainty however doesn't necessarily infer that solar forcing measures are bad. In fact, because there are direct measures now I would think contributes to the high degree of confidence that it is primarily human caused.

    There seems to me, however, to be an inconsistent standard in how we treat current measurements based on direct observation vs past measurements based on proxy data from reconstructed indirect evidence. In other words, some treat these earlier measures as if they are much more valid despite the limitations inherent in such reconstructions while holding direct measurements up to a much higher standard despite the fact that these are direct measurements. That's my 1 cent observation for the day :)
  8. GatorRade
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    I think this is right, and Oaktown agrees here. I think his problem was predicting future sunspot variations, which confused me too considering the IPCC's response here, but I think that my last post might clear this up.

    Clearly, this isn't the most prudent way of looking at the data, if true, but it is tough to turn down a story that you like.
  9. asuragator
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    asuragator Well-Known Member

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    Predictions about the long term future will always come with uncertainty, hence error bars on the CI.

    I guess my point is that even if there is still more to be known about solar forcing factors (when in science isn't there more to be known?), that human contributions are the most significant even when directly measured solar factors are factored in, it is not a problem that the IPCC claims high confidence. The problem seems to me that we want complete certainty when the language of science is probability and nuance.
  10. asuragator
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    asuragator Well-Known Member

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  11. GatorRade
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    GatorRade Well-Known Member

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    Definitely agree.

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