RadicalRodent asks "how CO2 could be such a greenhouse gas as claimed, it being such a tiny proportion of the atmosphere" if you want to know the scientific argument, I would recomment Raymond Pierrehumbert's book on "The Principles of Planetary Climate" as a good starting point. The basic mechanism was first clearly elicidated back in the 50s and 60s by Gilbert Plass, his papers are available online somewhere IIRC.

If you want an intuitive answer, I would say that the amount of energy the Sun transfers to the Earth is vast, but so is the amount that the Earth reflects and re-radiates back into space (indeed for global temperatures to stay stable, the two must be very evenly balanced). A small change in the proportion of this energy that is re-radiated is itself a very large amount of energy, and hence can have a significant effect on global temperatures. To put it more concisely, the reason such a small amount of CO2 to have such a large effect is because it modulates a vast flux of energy.

I am interested in science, I am not interested in blog-wars, so I am not going to be drawn into a discussion of that. The question was "So where are Salby and Darwall wrong .... precisely?", I have answered that, by pointing out that there is no mathematical connection whatsoever between the correlation Salby observes and the long term increase in CO2, and that Salby was unaware of the existing work that already explains the correlation. Lets discuss that.

Radical,
I think you may be directing things at Gavin when meaning me (sometimes at least). I'll make one final comment. I do really wish that we could have serious discussions about this topic and I appreciate that what I'm about to say may annoy you, but maybe you can think about it a little, at least.

You said,

I might be in error, but do not think so. I cannot remember where I have seen those figures, but it was on more than one site, and, to tell the truth, can’t be bothered looking for them again. I am dismissive of those who cannot find it as I feel that, if I can find it, then it cannot be too difficult to find.

I have looked. I can't find it. I find hoards of evidence that 22000 years ago CO2 levels were around 180ppm not 4000ppm. I also find hoards of evidence to suggest that it hasn't exceeded 300ppm (until this last century) for over a million years. So, you've made a statement that everything I've found suggests is wrong. You, however, choose to not back this up and simply claim that others should be able to find it since you managed to do so. You simply say "so what, I saw it, I can't be bothered to look again". That's fine, but maybe consider this when you criticise what happens on SkS. I also have no real sense of why you won't check and acknowledge your error, assuming you discover yourself to be wrong (as you probably will). It's no big deal and I certainly won't crow about it if you did. I'd be quite impressed, to be honest.

RadicalRodent wrote "Gavin, try reading what I write. I did not state or even infer that deep-sea vents were a source of CO2;"

fair enough, I accept that point. However they are still a small source of acidity, even compared to anthropogenic emissions (which would need to include suplhates etc. if other forms of acidity from deep-sea vents are included).

"Similarly, no-one has yet managed to answer my question as to quite how CO2 is the cause of AGW claimed for it, they just get objectionable."

I have attempted to do so in my previous post.

"Is CO2 the only gas involved in Henry’s Law?"

no, Henry's law applies independently to all soluble gasses.

"so the ratios of gasses dissolving or not in the oceans will be more or less as they are now"

no, this is not correct. Henry's law depends on the partial pressures of the gasses. If the amount of CO2 increases in the atmosphere, its partial pressure goes up, but the partial pressures of other gasses do not, so their solubility is unchanged.

"as CO2 is just 0.04% of the gasses likely to be dissolved (or not) in the oceans, we are not talking about a huge quantity in the scale of things, here"

Again it is the partial pressure of the gasses that determies their solubility, so this argument is incorrect. The partial pressure of CO2 has increased by about a third, which is why its solubility has increased so much.

"Now, you resort, once more, to the rise in CO2 being primarily anthropogenic (with little evidence to support this); "

I have given you a reference to my paper and also an article on SkS that outlines the multiple lines of evidence, so it is not correct to say that there is little evidence to support this, there is a lot of evidence to support this finding.

"why are the CO2 levels observed higher over the rainforests than over urban areas?"

CO2 in the atmosphere is well mixed, if you look under the inversion layer, you will find levels are very high over urban areas. Also rainforests contain more than just trees, I suspect you will find soil respiration is rather high in rain forests, and also trees also respire (produce CO2), the only CO2 they take out of the atmosphere permanently is that tied up in their annual growth. The carbon cycle is quite complicated, and you need to consider all factors. Without further details it is difficult to answer the question more fully.

" I have seen many sources where the proportion of human-generated CO2 is about 3-5% of the total rise;"

yes, this is explained in my paper, and is to do with the residence time. Essentially there are vey large exchange fluxes of CO2 between the atmosphere and the oceans and terrestrial biosphere. These rapidly exchange molecules of CO2 from fossil fuel use with molecules from natural sources (within about 5 years). However this is a straight swap and so does not cause an increase in atmospheric CO2. This is a very common misunderstanding of the cabon cycle on climate blogs. Ferdinand Engelbeen has been tireless (and very polite) in explaining this on a range of skeptic blogs, his website is a valuabel resource that you should investigate http://www.ferdinand-engelbeen.be/klimaat/co2_origin.html

" Is someone lying, or otherwise deliberately misleading?"

there is no need to introduce suggestions of dishonesty or malice. People make errors and they misunderstand things, that is explanation enough.

JohnShade If you email the author of a paper, they will quite often send you a pre-print if you ask (provided it is for personal use etc. and the journal's conditions permit it, which they do in this case).

"The fact that uncertainties in the sizes, and fluxes, of various natural sources and sinks are way larger "

You don't need to know the values of the uncertainties in the natural fluxes to deduce that the natural environment is a net carbon sink, and hence is opposing, rather than causing the rise in atmospheric CO2. You only need the annual growth rate, and anthropgenic emissions, the data on both of which Prof. Salby says are reliable. See the SkS link I gave earlier or my paper for details.

Humlum et al make the same mistake as Salby (the correlation in question has no mathematical connection whatsoever with the long term increase), and also was unaware of the work of Bacastow and others who have studied this issue before. Note that Humlum's paper was subject to a peer-reviewed comment paper that points out the flaws in paper.

Sorry if my posts are becoming a little terse, but there is only one of me, and a lot of points have been raised. They key point though is that the correlation that Salby and Humlum point out was already well known and understood, and has no mathematical connection whatsoever with the long term increase, so the argument based on it is fundamentally flawed.

FWIW, I would say that the carbon cycle is more like the planets main thermostat, rather than its control knob (as it mostly acts as a feedback in the pre-industrial world), but that our emissions are messing with the thermostat.

Gavin Cawley

FWIW, I would say that the carbon cycle is more like the planets main thermostat, rather than its control knob (as it mostly acts as a feedback in the pre-industrial world), but that our emissions are messing with the thermostat.

I'll repeat what I said earlier and ask isn't nature adjusting the thermostat on its own?

As far as I'm aware the evolution of C4 plant types occured about 25 million years ago, in response to falling CO2 concentrations. C3 plants are the majority at about 95% of all biomass need greater than 200ppm to survive. C4 plants are better in low CO2 and more arid conditions and are much better at carbon fixing at about 30% of the total currently. This suggests that a continuing decline in atmospheric CO2 content and a move to C4 carbon fixing by plants is quite likely without a natural process, such as increased vulcanism, which increases CO2 in the atmosphere.

Mike, no problem (it is usually my surname that gets mis-spelled - I'm quite used to that! ;o).

SandyS plants are a component of the carbon cycle thermostat, but I was thinking more of the weathering thermostat (high temperatures increase the rate of weathering of silicate rocks, which removes CO2 from the atmosphere, tending to regulate temperatures back down again over long timescales).

However, that is getting away from the key question "So where are Salby and Darwall wrong .... precisely?", which I have answered earlier in the thread. The correlation he discusses cannot explain the cause of the post-industrial rise as there is no mathematical connection between the two.

SandyS
"This suggests that a continuing decline in atmospheric CO2 content and a move to C4 carbon fixing by plants is quite likely without a natural process, such as increased vulcanism, which increases CO2 in the atmosphere."

You are partly correct. The earth has a natural thermostat that operates to draw down CO2 levels over very long time scales. Long being 10's of millions of years and longer. On these time scales the planet has two basic flows of CO2. Out of the Earth and into it. Volcanism is the long term source of Carbon being added to the surface. And a process called weathering reverses this and moves carbon back deep underground.

Weathering is a series of chemical reactions. First CO2 and water react in the atmosphere too produce carbonic acid - a very weak acid. This falls out in the rain and initiates chemical weathering in some types of carbonate and silicate rocks. Not erosion, more like very slowly dissolving them. The minerals dissolved eventually flow to the sea where they become part of the carbon cycle in the ocean. Ultimately they end up in the shells of tiny marine life that get deposited in sediments and eventually are subducted underground to eventually be vented as volcanic CO2 again 10's of millions of years later.

Importantly the chemistry of this weathering process is temperature dependent, running faster at higher temperatures. So if the earth is warmer weathering tends to draw down more CO2, cooling the planet. Conversely when it is cool it runs slower allowing volcanic CO2 to build up, warming the planet.

Since weathering is unconcerned with why the earth might be warmer it will tend to counter any warming influence - higher CO2 levels, warming Sun, whatever. So over very very long time scales the weathering system has tended to keep drawing CO2 down to compensate for a slowly warming sun.

But its not perfect and can be disrupted. Changes in volcanic activity can change the quantities of available rock surface on which weathering can occur, altering the weathering rate independent of temperature. Other processes might also impact on CO2 levels, compounding what the weathering system is doing. For example, during the Devonian and Carboniferous periods massive expansions in plants - the first great forests - locked up huge quantities of carbon then buried it as coal, We are burning that today. This altered the carbon balance so that a period of colder temperatures ensued.

So the weathering system is one factor that can twist the CO2 control knob, influencing climate. So too can volcanism and photosynthesis. And smart ape-persons who discovered fire. We all twist the knob from time to time.

RR (wrt 4000 ppm 1000's of years ago0
"I might be in error, but do not think so. I cannot remember where I have seen those figures, but it was on more than one site, and, to tell the truth, can’t be bothered looking for them again. I am dismissive of those who cannot find it as I feel that, if I can find it, then it cannot be too difficult to find."

Sorry RR but the ball is in your court. All the evidence I have ever seen says that CO2 concentrations have been at scales of 100's of ppm for 10's of millions of years. The last time CO2 was at 4000 ppm was well before the death of the dinosaurs. Ice core records going back nearly 1 million years for example put CO2 at between 180 and 280 ppm.

Over to you.....

RadicalRodent wrote "As for my comment: “Is someone lying, or otherwise deliberately misleading?” there is strong evidence that people are, on both sides of the argument, most likely for political and/or financial gain ..."

but say they are, does it mentioning it make the discussion more productive or less, in terms of getting to grips with the science?

"A good case in point is why is there such vehement denial about the 17-year pause in the rise in temperatures?"

I think this is another occasion where it is not dishonesty, but mistakes and misunderstaindings. I don't think anybody questions the fact that GMSTs have been quite flat since about 1998. However that does not mean that the underlying rate of warming is unchanged, or that anthropogenic global warming has stopped. This is because estimating a trend in noisy (autocorrelated) signals is subject to uncertainty, and currently, this uncertainty does not exclude the possibility that global warming has stopped, but it doesn't exclude the possibility that it has continued at the same rate and that the apparent hiatus is just an artefact of weather noise. Part of this is due to a lack of understanding of statistical tests of trends (I work in a branch of statistics, so the errors are fairly easy for me to spot, but not for someone without a good statistics background).

The hiatus is not ignored, it is actually quite widely discussed in the literatire, because it is interesting. See for example the recent special issue of Nature Geoscience on this topic http://www.nature.com/ngeo/focus/slowdown-global-warm/index.html .

There is no vehement denial of the 17 year hiatus, but there is genuine disagreement on what it actually means, and climatologists have taken the time to investigate in detail (e.g. Easterline and Wehner's paper).

So in this case, it is very obviously a case of error and misunderstanding, rather than dishonesty and misrepresentation.

There is a thing called Hanlon's razor, which says that "never attribute to malice that which can be adequately explained by stupidity". I prefer a more moderate version of it, namely "always interpret the comments and behaviour of others in the best light that is consistent with the observations". While there are dishonest people in the world, it does us no good to go looking for more of it, or to see it where it actually doesn't exist and it is just our error or misunderstanding.

Anyway, this is getting further and further from the key topic, which is "So where are Salby and Darwall wrong .... precisely?". As I have explained, this lies in detrending the CO2 data (by looking at the growth rate) before comparing it with temperature (correlations being insensitive to additive constants, which is what the trend becomes after differentiating to get the growth rate).

I baulk at having to pay $35 to read one of his papers which he links to.

That's why world class university research libraries are free and open to the public. I think it costs at most 10 cents a page to copy these articles or print out the pdfs. You have no excuses for not following the literature when your naive and silly arguments are dismissed or destroyed by those who do. Find a free two hour parking space, walk and do the work.

shub wrote "How refreshing it is to discuss matters openly, huh Gavin? Instead of hiding at welloinkedcatherd?"

sadly this sort of thing is pervasive in discussion of climate on blogs. Sorry, I would be happy to have a polite discussion of the science, but I have no interest whatsoever in partisan "blog wars" rhetoric like this. So if you want me to continue the discussion with you after this post, please adopt a more reasonable and scientific tone.

The point made by the escalator diagram is just as valid today as it has ever been, which is that cherry picked short term trends, are meaningless. There are good statistical methods for analysing trends (e.g. as implemented in the SkS trend calculator). If you look at the error bars on the trend estimates for such short periods, you will find them to be so wide that you can't draw any conclusion from them. The problem is in asserting that the apparent hiatus in GMSTs mean there has been a hiatus in the underlying rate of warming. This is not correct as a proper statistical analysis shows that the hiatus is still plausibly an artefact of weather noise. The purpose of the nature article is to understand the reasons for the hiatus and to determine whether it actually is an artefact or whether there has been a change in the underlying rate of warming.

Personally, I suspect it is probably mostly artefact, because ocean heat content has continued rising, which suggsts the hiatus is simply due to a change in the exchange of heat between the surface and oceans, but the planet as a whole is still accumulating heat at much the same rate. This is reinforced by the evidence of Foster and Rahmsdorf, which suggests the hiatus largely goes away of you account for the effects of ENSO.

Mike Jackson wrote "... the history of climate in the 20th century and, as far as we have accurate records, the 19th century also is of ~30 years of warming, ~30 years of cooling/stasis, and so on to about 2000"

The human eye is all too good at seeing patterns and cycles in noisy data, where no underlying cyclical physical process is actually at work, and instead the apparent cycles are due to the interplay of a variety of other factors and the noise. In the case of climate, long term temperature variations depend on a wide variety of forcings, including solar, volcanic and anthropogenic forcings. None of these have been constant over this period, so for there to be an actual cycle, you first need to show that the cycle still exists once these known forcings are properly taken into account, or show that the climate does not respond to these forcings. Most attempts to model the climate using such cycles (e.g. Loehle and Scafetta) notably ignore the forcings, and so find a cycle where none (likely) really exists.

"And yet the consensus establishment is using every trick it can think of, from "the ocean ate my warming" "

these aren't tricks, they are genuine attempts to understand the observations using physics (apart from the rhetorical label). ENSO is known to have a big effect on GMSTs (water has a very high heat capacity relative to the air, so you only need a fairly small change in ocean temperatures to have a substantial effect on GMSTs). Thus controlling for the effects of ENSO is a perfectly reasonable thing to do in investigating the hiatus, even if it isn't represented that way on the blogsphere.

"to insist that this is only a pause"

IIRC, the special issue of nature contained some papers that did not say that the underlying rate of warming had continued. There are certainly papers (e.g. Fyfe that contend that models have overestimated climate sensitivity based on the hiatus, although I think in that particular case the statistical argument is flawed). So it is not the case that the mainstram scientists are insisting anything, it is very much up for discussion, hence the special issue of Nature.

"And they provide no convincing reason to back up their argument. "

no, as I pointed out, it would be very strange if ENSO and ocean circulation in general didn't have a substantial effect on GMSTs.

"Hand-waving, assertion, lots of 'may', 'might', 'consistent with', obfuscation, insult even. "

There is no hand-waving in Foster and Rahmstorfs paper, but solid statistics. Also "may" "might" "consistent with" are the language of science. Science frequently cannot give unequivocal answers, and not overstating your findings is key to good science, hence the use of such terms. Note "consistent with" has a specific statistical meaning, which is quite important as "not consistent with" is a very strong statement. Regarding obfuscation, it is better to assume that you are missing some subtle point rather than that the point is being obfuscated, self-skepticism is central to being a scientist. Afterall, they are the ones who have invested their careers in investigating this problem so they pobably understand it better than you do, so if you assume it is your own error, you will usually be right.

"We don't need to be talking climate here; those of us with years of experience in business, education, local government, you name it, recognise the signs. "

I think your background is leading you astray then. Science is *very* differnt to business and governement, The vast majority of scientists pursue their work out of curiosity and go where the evidence takes them. It is a career limiting move to do otherwise as if you deliberately follow an agenda that isn't supported by the facts, you will quickly be found out and your reputation will be in tatters.

"CO2 is supposedly the main driver of late 20th century warming."

that woulld be a reasonable summary of the IPCC position

"CO2 started to increase around 1800-1850 and yet it had no effect (the consensus says) until 1975."

no, that is not correct. It is not true that it had no effect prior to 1975, just that it became the dominant effect after about 1975. There is also the fact that e.g. aerosol forcing has been masking some of the effects of GHGs, and legislation has resulted in a reduction in this masking. The IPPC position is that you need both natural and anthropogenic forcings to explain the observed climate of the 20th century, which seems a pretty reasonable position to me.

"CO2 continues to increase and yet there has been no warming since 1997."

The expected rate of warming due to CO2 is quite small compared to the effects of internval climate variability (such as ENSO) on short timescales. As Easterling and Wehner showed, it is not unusual to see decadal or longer periods with little or no warming in the presence of a long term trend for this reason. We see it in the observations, and we see it in model output as well (but the models cannot predict when they will happen). For an example of a previous decadal trend with no warming, see this plot of RSS temperatures: http://i.stack.imgur.com/3rcib.png

"Don't you see a major disconnect here?"

No, I see some misunderstanding of issues in statistics and climatology, but no major disconnect.

"And then ask yourself the age-old question, cui bono?"

Physics doesn't depend on motives. As I have pointed out, it is a career limiting move for scientists to do anything other than follow where the evidence leads. Scientists (and academics in general) make a living by proving each other wrong, that is largely how science proceeds (ask Karl Popper), so the idea they are all in some sort of organised deception for personal gain is a non-starter. It isn't as if being a scientist is a particularly profitable career (compared with business or government), and the scientists don't get to keep the grant money anyway, most of it goes on hiring research assistants.

I think that will be my last post here. Once discussion of science moves onto discussion of motives etc. the chances of reaching agreement on the science rapidly diminishes. I hope the explanation of the particular error in Salby's reasoning is of interest; if anyone wants a copy of my paper, send me an email.