Nir Shaviv explains climate sensitivity

Transcript of the introduction of talk by Nir Shaviv, skeptical Astrophysicist, at the 2009 Heartland Conference entitled: New solar climate links and their implications to our understanding of climate change (listen to audio).

In the introduction, Nir explains the concept of climate sensitivity very clearly. After this, one can understand the origin of such claims as ‘if the hockey stick is wrong, then sensitivity is higher than we thought and global warming will be worse’.

OK I am glad to see the number of people who have evaporated is not very large in this last 5 min break.

To answer a question that was asked before I think one of the problems with the models, first of all with respect to feedback, it is cloud cover. That because you cannot resolve very small scales the cloud cover physics is basically parameterized with a recipe, and because its parameterized with a recipe, whichever recipe you decide to use, whatever you cook depends on the recipe that you use.

So that’s one thing. The models are incorrect because they don’t include all the related forcing of all physics that the models should include.

Anyway, I am going to talk about relatively new results on the solar climate link. We have seen a lot of evidence even today that the sun has a large effect on climate, but if you want use it or enter it into models you need to know how large is it, not only that it is important qualitatively but also quantitatively how large is this relative forcing. So this is what I am going to talk about today.

So how strong is this radiative forcing and why is it important for example to understand climate change? So I am going to begin with trying to elucidate why knowing the relative forcing is important then I go ahead describing how you can use the oceans as a big calorimeter to measure this relative forcing then talk about implications.

Why is knowing the relative forcing important? First of all it’s interesting because you want to explain the climate — you want to understand what’s driving it. With respect to global warming it’s interesting because if you look at the 20th century warming you see that there was some type of warming over the 20th century, its 0.6 or 0.7 or who knows what. You want to explain it with some kind of radiative forcing. Of course natural fluctuations can be important as well but I am not going to talk about them.

You know there is a given change in temperature, and you want to know what is the relative forcing, because the radiative forcing times the sensitivity of the climate — namely how the climate behaves following changes in relative forcing — this thing is going to translate into a given temperature. So if you try to explain 20th century temperature increase with a small relative forcing you will necessarily need a model with large sensitivity. If on the other hand the sun is important over the 20th century it means that the total radiative forcing over the 20th century is going to be larger. If you have a larger radiative forcing then the same given change in temperature should be explained with a lower climate sensitivity.
Basically climate sensitivity is the trillion dollar question because if we know what the climate sensitivity is, it will tell us how much the temperature is going to increase because of us humans over the 21st century and so on. The biggest question is what is this radiative forcing of the sun?

This is an example, one of the nicest examples I know of the fact the sun affects the climate. It’s a qualitative result. What you see here on one, you see a proxy for solar activity, it is in fact a proxy for cosmic rays which we now know is probably the thing which drives climate and that’s the carbon 14 that you get out of tree rings. Carbon 14 is formed by spallation from cosmic rays which hit the atmosphere by but these are modulated by the sun. So the upper graph that you see is solar activity. The bottom graph is the O18/O16 ration from a cave in Oman. There are other very nice results but this is one that is particularly nice. So you see that there is a big correlation between solar activity and climate and the question is: is it driven for example by changes through total solar irradiance and super high climate sensitivity or is it driven by some other mechanism? So you want to quantify the effect somehow.

So what we want to do is use the oceans.

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0 thoughts on “Nir Shaviv explains climate sensitivity

  1. “After this, one can understand the origin of such claims as ‘if the hockey stick is wrong, then sensitivity is higher than we thought and global warming will be worse’. ”

    I guess I’m dense. I don’t follow this, even after listening to Shaviv and reading the above.

  2. “After this, one can understand the origin of such claims as ‘if the hockey stick is wrong, then sensitivity is higher than we thought and global warming will be worse’. ”

    I guess I’m dense. I don’t follow this, even after listening to Shaviv and reading the above.

  3. If the variation in global in temperature is greater (eg. MWP is higher) than projected for a small change solar forcing, then the climate sensitivity is greater than expected, and so response of global temperatures to an increase in forcing from CO2 increase would be greater than expected.

    Delta Temp = Sensitivity X Delta Forcing
    Deg C = Deg C/Watts.m^-2 X Watts.m^-2

  4. If the variation in global in temperature is greater (eg. MWP is higher) than projected for a small change solar forcing, then the climate sensitivity is greater than expected, and so response of global temperatures to an increase in forcing from CO2 increase would be greater than expected.

    Delta Temp = Sensitivity X Delta Forcing
    Deg C = Deg C/Watts.m^-2 X Watts.m^-2

  5. davids: Thanks. But how do we know what forcing was necessary to cause the MWP? It could have been a very large forcing, no? I can see the point if we knew that the MWP was caused by a small forcing.

  6. davids: Thanks. But how do we know what forcing was necessary to cause the MWP? It could have been a very large forcing, no? I can see the point if we knew that the MWP was caused by a small forcing.

  7. jae-yes, that’s exactly why that claim is bogus. We have no idea what the forcing which caused the MWP was, let alone its magnitude-sure, we have hypotheses, but saying “if these hypotheses are correct, but our climate history is not variable enough, we need a higher sensitivity” is then the correct thing to say, not “if our climate history is too stable, we need a higher sensitivity”. Ultimately, my view is that some forcing or source of variability will be found which explains the MWP with a rather small sensitivity value. Anyway, the other problem with that argument is that in order for that to be true, you would also need an unrealistic aerosol forcing history to mask really massive AGW-but there is no basis for that. If the MWP has been underestimated, the ~only~ internally consistent conclusion is that natural variability has been underestimated, which says nothing about sensitivity.

  8. jae-yes, that’s exactly why that claim is bogus. We have no idea what the forcing which caused the MWP was, let alone its magnitude-sure, we have hypotheses, but saying “if these hypotheses are correct, but our climate history is not variable enough, we need a higher sensitivity” is then the correct thing to say, not “if our climate history is too stable, we need a higher sensitivity”. Ultimately, my view is that some forcing or source of variability will be found which explains the MWP with a rather small sensitivity value. Anyway, the other problem with that argument is that in order for that to be true, you would also need an unrealistic aerosol forcing history to mask really massive AGW-but there is no basis for that. If the MWP has been underestimated, the ~only~ internally consistent conclusion is that natural variability has been underestimated, which says nothing about sensitivity.

  9. “Ultimately, my view is that some forcing or source of variability will be found which explains the MWP with a rather small sensitivity value.”

    The CRF theory fits the bill. Here the MWP is due to amplified solar radiance, and low sensitivity.

    What has gone on is that by not taking CRF amplification of forcing into account, the observed small variations in solar radiance, necessitate assumptions of high sensitivity to produce the temperature variations, of the MWP, and also glacial-interglacial transitions, and ‘recent’ warming. When this new CRF forcing is taken into account, these variations are largely explained, and sensitivity drops to a value consistent with neutral feedback, black-body response.

    In other words, appearance of high climate sensitivity results from omission of a pertinent forcing factor in the equations. The unstable nature of GCMs is probably due to this high sensitivity. When the pertinent factor is included in empirical models, poof, the sensitivity stabilizes to uninteresting levels. The climate system simply becomes a passively driven system.

    Mathematically there are three unknowns, and we need to know 2 of them to get the other one. The various experiments and statements need to be considered in the light of which of them is measured, assumed, and inferred.

  10. “Ultimately, my view is that some forcing or source of variability will be found which explains the MWP with a rather small sensitivity value.”

    The CRF theory fits the bill. Here the MWP is due to amplified solar radiance, and low sensitivity.

    What has gone on is that by not taking CRF amplification of forcing into account, the observed small variations in solar radiance, necessitate assumptions of high sensitivity to produce the temperature variations, of the MWP, and also glacial-interglacial transitions, and ‘recent’ warming. When this new CRF forcing is taken into account, these variations are largely explained, and sensitivity drops to a value consistent with neutral feedback, black-body response.

    In other words, appearance of high climate sensitivity results from omission of a pertinent forcing factor in the equations. The unstable nature of GCMs is probably due to this high sensitivity. When the pertinent factor is included in empirical models, poof, the sensitivity stabilizes to uninteresting levels. The climate system simply becomes a passively driven system.

    Mathematically there are three unknowns, and we need to know 2 of them to get the other one. The various experiments and statements need to be considered in the light of which of them is measured, assumed, and inferred.

  11. “But how do we know what forcing was necessary to cause the MWP? It could have been a very large forcing, no? I can see the point if we knew that the MWP was caused by a small forcing.”

    We don’t know. The idea is we need to know both forcing as well. Claims of high sensitivity make the assumption of small forcing (from TSI). The discovery of a large, unaccounted for forcing (CRF) removes the need for a high sensitivity to explain large temperature changes.

  12. “But how do we know what forcing was necessary to cause the MWP? It could have been a very large forcing, no? I can see the point if we knew that the MWP was caused by a small forcing.”

    We don’t know. The idea is we need to know both forcing as well. Claims of high sensitivity make the assumption of small forcing (from TSI). The discovery of a large, unaccounted for forcing (CRF) removes the need for a high sensitivity to explain large temperature changes.

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