John Nielsen-Gammon and I have continued our discussion that we started in the post
With a few edits, with John’s permission, I have reproduced our e-mail communications below.
Hi John. Thanks for the quick feedback. I will go ahead and post your reply.
I have this point of disagreement – you are (incorrectly in my view) equating global warming with the subset of warming caused by CO2 and a few other human inputs of greenhouse gases.
Response from John
You might not agree with my numbers, but I do explicitly deal with “the issue of the relative contribution of greenhouse gases to global warming” in my comment, rather than equating the two. Thanks again!
I am then unclear on your text. You write
“I concluded (conservatively, I would say) that about a half degree to a degree was attributable to anthropogenic greenhouse gases.”
[which seems reasonable]
“…summer temperatures would have been about one half to one degree cooler without the increases in CO2 and other greenhouse gases.”
so far so good…the two statements above say the same thing.
But, you also write in your original post
“With the uncertainties over response times and feedbacks, the amount of observed warming over the past century plausibly attributable to anthropogenic increases in the concentration of greenhouse gases may be as small as 0.5F and may be as large as 2.0F, in my opinion. I picked 1.0F, but whatever the actual value is, it is unquestionably positive and enhanced the severity of the drought.”
“The actual summertime temperature was 86.8 F, so 4.0 F out of the 5.4 F of excess heat (74%) was a consequence of the drought itself.”
this leaves 1.4F from circulation effects and the other positive radiative forcings. I am assuming the “drought” effect means the greater sensible versus latent heat effect.
If there was no circulation effect, I can see how you could obtain 0.7F (i.e. 50% from CO2 as an upper bound) but certainly not 1F or 2F. Anyway, please clarify and I will add to the post.
I also would really like to see your analysis of the drought in terms of surface moist enthalpy. :-)
About the moist enthalpy, I could speculate…it’s faster…..presumably the sensible/latent effect partly mitigates moist enthalpy intensity vs. temperature intensity, but one other sensible/latent effects (decrease of cloud cover) means there should still be a moist enthalpy signal and a third effect (increased PBL height) probably works to decrease the moist enthalpy but I would guess not enough to overwhelm the cloud cover effect.
The 1.4F (+/- uncertainties in the 4.0F attribution) is what results from circulation effects and the combined effect of positive AND NEGATIVE radiative forcings. Because much of the effect from CO2 and other anthropogenic greenhouse gas emissions will have been counteracted in part by negative forcings such as aerosols, the observed rise does not represent an upper bound on the anthropogenic greenhouse gas effect.
“……You also have much more confidence in the IPCC modelling than I do. Their failure to properly predict the current cool-down, the one after 1998, etc should raise a concern that they do not properly handle circulation effects. Even more clearly, they have no regional skill, which is what determines temperatures for Texas.
In a strange way, I have much less confidence in the IPCC modelling than you do. You seem to think that they should be able to predict the full atmospheric response to all future forcings as well as natural variability, since that’s what it would take to properly predict the full temperature (or OHC) variations over the past 13 years. Since the AR4 model runs did not include 3-D initialization of the oceans, nor any predictions of solar activity, nor any predictions of volcanic activity, I do not expect them to be nearly as capable as you do. I expect the AR4 runs to simulate a response to projected concentrations of CO2 and other GHG within scientifically plausible bounds of sensitivity in a dynamically self-consistent way, which they do.
With this assumption, you could claim that the CO2 effect covered ALL of the 1.4F (and more attribution).
However, there is no way to confirm this conclusion as in the real world we cannot separate out the effect of just one climate forcing. Moreover, I assume you are including the water vapor feedback into this number.
However, if the atmospheric water vapor does not increase (and in recent years it has not), there is no amplification of the CO2 radiative forcing (or any other positive or negative radiative forcing). Your assumption is based on models which, as shown just a few days ago by Bob Tisdale
An Initial Look At The Hindcasts Of The NCAR CCSM4 Coupled Climate Model
is not able to skillfully predicting the behavior of the climate system during the last several decades.
Also, the issue of the role of added CO2 on the drought does not depend on what its maximum radiative forcing would be, but rather what fraction of the drought was a result of the added CO2 that was actually affecting the weather pattern. I do not see how we can answer that, as the models have not shown such regional skill.
All we can say (as with any weather pattern) that the added CO2 had an effect.
When driven by observed oceanic variability, the models do a great job simulating the atmospheric response. With the present drought, it’s not a matter of predicting the oceans and atmosphere. We know the present ocean temperature patterns, so we can estimate their contribution very well from both observations and models. The models’ difficulty in simulating the statistics of ENSO itself is a red herring.
I also disagree with your philosophy/epistemology of attribution regarding weather patterns, but that’s a whole other issue.