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More pointed questioning of AGW

H/T Messenger for this podcast by Professor Murray Salby of Macquarie University. Salby looks to be pretty mainstream, having published with Susan Solomon and Martin Juckes among others. The message appears to be that much of the rise in atmospheric carbon dioxide may be natural and caused by non-anthropogenic warming.

Andrew Bolt summarises the talk here, noting Salby's comments that anyone who thinks global warming science is settled is "living in Fantasia".


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Reader Comments (84)

Rhoda: "Well, even a sceptic might agree that 6 gigatons produced by man might just make a difference when the measured annual increase is only 3GT"

How does mother nature know to raise atmospheric CO2 by EXACTLY 50% of the CO2 supposedly produced by man?

Why not 100%? Why not 66.67%?

Why does a 1% in CO2 overwhelm poor old mother nature when she herself changes the amount of Co2 by 6x or 7x mans supposed contribution?

And what about C4 plant life like corn absorbing more C13 versus C3 plant life absorbing more C12?

Aug 4, 2011 at 7:01 PM | Unregistered CommenterBruce

Bruce, if we didn't put in 6GT, maybe it would not be increasing. That's all. Now, it may be that it would still increase, because of overwhelming natural factors. It could be, but Occam says that it wouldn't be increasing, or not by so much, if we weren't burning stuff. I make no claim of exactly 50% and I do not believe anybody has got a real handle on the sources and sinks. to the extent that I'd say anybody who made such a claim was either a guesser or a liar. Either way, sceptics need not rely on this one (that the fossil fuel burning has no effect) as an argument, we don't need it and it is a probable loser.

Aug 4, 2011 at 8:27 PM | Unregistered CommenterRhoda

Bruce --
The increase of atmospheric CO2, relative to anthropogenic effects, isn't exactly 50% -- although the CO2 concentration in the atmospheric is well measured, the emissions are only known approximately. And the effects from land-use (e.g. deforestation) is even less well-known.

It's true that the natural exchange of CO2 far exceeds anthropogenic emissions. See, for example, this chart from AR4, in which the natural fluxes are shown in black and the anthropogenic ones in red. One can see a little bit of this by looking at the seasonal variation of pCO2 which exceeds the year-on-year increase. However, it's still plausible that the increase in CO2 is mainly anthropogenic. The argument is that CO2 reached a state of approximate equilibrium over the millennia of the Holocene, such that there was no long-term trend, or only a small one, in the pre-industrial era. [The annual cycle would of course still be present.] The amount emitted each year more or less balanced the amount taken up. The addition of anthropogenic sources of CO2 would, in the absence of a feedback cycle, result in increases to atmospheric CO2.

However, as Paul Dennis mentions above, there *are* feedbacks -- natural carbon sinks are stronger. Plants grow faster, thereby removing more CO2 from the air. From Henry's law, the higher proportion of CO2 in the air drives more CO2 into the ocean. The direction of these feedbacks is known; the exact amount seems to be in question. As of AR4, it was thought that the increased carbon sinks offset about half of the anthropogenic effects. Paul Dennis suggests that we don't know the precise strength of the sinks. We don't know exactly the size of any non-anthropogenic imbalance, but ice core data indicate that historically, any imbalance is small compared to, say, the past 50 years of measured pCO2 increase. What we *do* know well is the net increase in CO2. It is less than the anthropogenic emissions, so it seems eminently logical (to me, at least) that the increase is predominantly due to man.

Whether said increase is dangerous is another matter.

Aug 4, 2011 at 8:27 PM | Unregistered CommenterHaroldW

Rhoda, HaroldW ... the 50% is just plain weird.

"While you have probably seen graphs of the atmospheric carbon dioxide concentration slowly increasing over time, the graph above shows the yearly growth RATE, as well as the estimated yearly rate of emissions by humanity. It shows a couple of interesting things. First, the growth rate of atmospheric CO2 is, on average, only about 50% of what mankind emits. This means that Mother Nature takes out about 50% of the ‘excess’ CO2 that we pump into the atmosphere every year. And it seem like it doesn’t matter how much MORE we put in each year…nature still takes out an average of 50% of that amount."

-- Roy Spencer

Aug 4, 2011 at 9:30 PM | Unregistered CommenterBruce

I can only agree with Paul Dennis and HaroldW

That humans are the cause is quite sure:
- The mass balance: It is impossible that nature was a net contributor to the increase, because the measured increase is less than the emissions. Thus nature was a net sink for CO2 over the past at least 50 years. As long as the Law of non-destruction of mass holds. In every year, the emissions were larger than what remains in the atmosphere, the difference must go somewhere (and it’s not escaping to space!), it is absorbed by oceans and vegetation. Thus there were (near) always more natural sinks than sources. Thus all natural emissions were completely absorbed (in mass, not in origin of the molecules) by natural sinks and the natural emissions were just part of the turnover, not contributing to the total mass in the atmosphere. It doesn’t matter if human emissions were 3% or 0.3% or 0.03% of the turnover, because the human emissions were additional, the natural emissions were not.
- The 13C/12C ratio: Indeed there are two main sources of low 13C: fossil fuels and the decay of vegetation. But the earth is greening, thus there is more CO2 absorbed by vegetation than that organic matter decays. That is confirmed by the oxygen balance: less oxygen is used than calculated from fossil fuel burning, thus the biosphere was a net source of oxygen, thus a net absorber of CO2 and preferentially 12CO2, leaving relative more 13CO2 in the atmosphere. But we see a decline of 13CO2 in the atmosphere…
- The process characteristics: The increase in the atmosphere follows the emissions with an incredible fixed ratio. There is no natural process which is able to follow human emissions in such a way, Natural processes are far more variable.
A few other problems:
- While there is an extremely good correlation between accumulated emissions and accumulation in the atmosphere, the correlation is less when one looks at the year by year increase, simply because temperature changes have a short term influence (about 4 ppmv/degr.C) on the increase rate, not on the trend! The long term influence, as seen in ice cores, is about 8 ppmv/degr.C. Even an increase of 1 degr.C since the depth of the LIA would not give more than 8 ppmv increase, not the 100+ ppmv as measured. BTW the pCO2 of seawater increases with not more than 16 ppmv/degr.C. And while any temperature increase should decrease the total amount of carbon in the upper layer of the oceans, we see an increase in carbon (and a decrease in 13C/12C ratio)
- Ice cores, tree carbon and coralline sponges all give small 13C/12C variations over the Holocene, but all show a steady and ever faster decline since about 1850. See:

See further my take in this discussion:

Aug 5, 2011 at 12:05 AM | Unregistered CommenterFerdinand Engelbeen

Joanne Nova has the clearest possible summary of Salby's presentation.

The largest increases year-to-year [CO2 levels] occurred when the world warmed fastest due to El Nino conditions. The smallest increases correlated with volcanoes which pump dust up into the atmosphere and keep the world cooler for a while. In other words, temperature controls CO2 levels on a yearly time-scale, and according to Salby, man-made emissions have little effect.

The climate models assume that most of the rise in CO2 (from 280 ppmv in1780 to 392 ppmv today) was due to industrialization and fossil fuel use. But the globe has been warming during that period (in fact since the depths of the Little Ice Age around 1680), so warmer conditions could be the reason that CO2 has been rising.

Salby does not dispute that some of the rise in CO2 levels is due to man-made emissions, but found that temperature alone explains about 80% of the variation in CO2 levels.

"Salby was once an IPCC reviewer, and comments, damningly, that if these results had been available in 2007, 'the IPCC could not have drawn the conclusion that it did.' I guess he’s also giving them an out."

Is it just me or do you notice the timing of this non-orthodox, thinking outside the box, scientific criticism? Salby held off on this for one year, plus six months... And that happened about 18 months ago? Climategate. Did this scandal make climate scientists more courageous?

Aug 5, 2011 at 12:06 AM | Unregistered CommenterOrson

What happened to the two posts I made in here?

Aug 5, 2011 at 12:16 AM | Unregistered CommenterDung


1) the Eemian had a 100ppm rise in CO2 without mans influence.

2) "But we see a decline of 13CO2 in the atmosphere…"

I'be told that C4 metabolism plant life has a preference for 13CO2 and "maize, sugar cane, millet, and sorghum" are C4's/ Those crops are immense.

The US has 92 million acres in corn. 30% of all crops.

Aug 5, 2011 at 12:46 AM | Unregistered CommenterBruce

"Today, sugarcane is grown in over 110 countries. In 2009, an estimated 1,683 million metric tons[3] were produced worldwide which amounts to 22.4% of the total world agricultural production by weight"

Aug 5, 2011 at 12:47 AM | Unregistered CommenterBruce

PaulM: "This is interesting and surprising. I had always thought that "the CO2 rise is natural" was one of the weaker sceptic arguments"

Yeah it is. In fact I wouldn't say weak, I would say utterly stupid. How can it be natural when both the oceans and biosphere have been drawing CO2 out of the atmosphere not adding to it, and when the rate of human CO2 emissions are two times larger than the rate of CO2 accumulation in the atmosphere?

It's a *travesty* that skeptics widely don't understand any of this.

Aug 5, 2011 at 1:07 AM | Unregistered Commenterbob

bob, whats a tragedy is that you don't get that CO2 accumulation fluctuates with temperature.

CO2 accumulation always follows temperature rises. Not the other way around.

Aug 5, 2011 at 1:14 AM | Unregistered CommenterBruce

There is much useful information about the carbon cycle and the derivation of the various fluxes at the Global Carbon Project. In particular, the figures given there conflict with Manning & Keeling 2006 and are more consistent with Paul Dennis' statement of approximately equal contributions from land and ocean sinks.

Regarding the relationship between anthropogenic effects and atmospheric CO2 changes, Le Quéré et al. 2009 (cited at the above website) states

Between 1959 and 2008, 43% of each year's CO2 emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO2 emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%

Aug 5, 2011 at 4:35 AM | Unregistered CommenterHaroldW

HaroldW, I'm assuming such ratios come from C12/C13 ratios.

I don't think they can be relied on.

“Today, C4 plants represent about 5% of Earth’s plant biomass and 1% of its known plant species.[11] Despite this scarcity, they account for about 30% of terrestrial carbon fixation.”


“C4 metabolism plants absorb more C13 than do C3 metabolism plants”

“Over the last 100 years we’ve planted one heck of a lot more grasses world wide than ever before. Grasses are often C4 metabolism…”

– Chefio

Aug 5, 2011 at 4:43 AM | Unregistered CommenterBruce

Bruce --
The fraction of anthropogenic emissions which remains in the atmosphere is not tied to isotopic concentrations, as I understand it. From the Global Carbon Project, emissions are based on energy and cement production. Land use effects are based on deforestation statistics. The sum of the two comprises the denominator, total anthropogenic emissions. [I dislike the use of "emissions" to refer to land-use changes; deforestation is a reduction of CO2 uptake rather than actual emission. But it seems to be a common usage, so with a grumble I acquiesce.] The numerator, atmospheric CO2 change, is computed from the atmospheric CO2 concentration, as measured at Mauna Loa and elsewhere.

I don't see isotopic distribution mentioned at all on that page, nor in Le Quéré et al. 2009.

Aug 5, 2011 at 5:25 AM | Unregistered CommenterHaroldW


The mass balance is the main argument for humans as cause of the increase in the atmosphere. As long as the increase in the atmosphere is less than the human emissions, nature as a whole is a net sink for CO2. No matter the 13C/12C ratio.

But the 13C/12C ratio gives additional strength to the above. The 13C/12C ratio (expressed as d13C) excludes the oceans as source, because any huge release from the oceans would increase d13C (including 2-way fractionation at the surface), as the oceans are zero to +5 per mil d13C and the atmosphere is currently at -8 per mil and declining.

The same for volcanoes and rock weathering, both are near always around zero per mil d13C.

The only possible alternative source is vegetation decay, but the oxygen balance shows that vegetation growth exceeds vegetation decay, thus that too is excluded. Moreover, it would need burning of about 1/3rd of all vegetation on earth to explain the increase.

What rests is the human emissions, which fit all observations...

BTW, the C4 cycle captures more 13C than the C3 cycle, but still shows a deficit in 13C compared to the atmosphere...

Aug 5, 2011 at 8:55 AM | Unregistered CommenterFerdinand Engelbeen

There is no natural balance between sources and sinks of CO2. We are dealing with a dynamic and unbalanced system.

Now it has been indentified that at least 80% of net atmospheric CO2 emissions are natural in origin and are driven by temperature.

There goes another leg of the AGW arguement. i.e., humans are responsible for the increasing levels of atmospheric CO2 and it is this man-made increase that is reponsible for increasing global temperatures. That is now nonsensical.

To summarise;

1. No Hot-Spot

2. No accumulation of heat in the oceans.

3. No human fingerprint in the increase of atmospheric CO2 over the past 60 years.

4. The AGW hypothesis is collapsing.

Aug 5, 2011 at 9:36 AM | Unregistered CommenterMac

There appears to be a misconception about C3 and C4 plants with some saying that C4 plants have a preference for 13-C. This is a misunderstanding. Typically C3 plants have a d13C composition of about -25 parts per thousand when compared to marine carbonate. C4 plants have a d13C composition of about -15 parts per thousand when compared to marine carbonate. Both photosynthetic pathways C3 and C$ discriminate against 13C in atmospheric CO2. C3 plants rather more than C4 but increased production of C3 and C4 plants and crops will result in an enrichment of 13C in the atmosphere.

Aug 5, 2011 at 10:24 AM | Unregistered CommenterPaul Dennis

Lord B

"when he invited scientists he trusted and admired to comment on the paper, they also sat on it for half a year"

I expect they did - thinking hard about how it might affect their research budgets and how a different interpretation might apply. It seems telling that they had to acquiesce...

Aug 5, 2011 at 10:54 AM | Unregistered CommenterJames P

Mac -
The argument for the approximate pre-industrial balance of CO2 rests mainly on the CO2 composition of the trapped air within ice cores. While it is likely that the process suppresses detail in the annual or even decadal variation, I think it is accurate at the centennial or millennial level. With that as prologue, please look at this graph. At the start of the Holocene, CO2 concentration was below 200 ppmv. It rose during the interglacial, but stayed below 300 ppm until the last century or so (the industrial era). While this evidence wouldn't preclude variation of, say, 10 ppm over a few years, it rules out larger and longer-term variation such as we are experiencing now.

Aug 5, 2011 at 12:40 PM | Unregistered CommenterHaroldW


As Salby clearly pointed out that even relatively recent ice core data are not a direct indication of past levels of atmospheric CO2. You cannot point to ice core data graphs and say 100,000, 10,000, 1000, 500 years ago the atmospheric CO2 was 'xxx' ppm and that over the entire glacial and inter glacial series varies between 'yyy' ppm and 'zzz' ppm

Salby also pointed out that over the past 50 years changing levels of atmospheric CO2 are more sensitive to temperature than previously thought.

So taking the arguement forward, you cannot now discount the likelihood that levels of atmospheric CO2 during warm periods in the past were of the same magnitude that is being directly measured currently.

Aug 5, 2011 at 2:57 PM | Unregistered CommenterMac


In addition, the Law Dome ice cores have a resolution of 40 years for the past 1,000 years, resp. 10 years for the past 150 years, showing the huge increase in CO2 over the past centuries. The cores also have a 20 year overlap with the direct measurements at the South Pole, see:

Aug 5, 2011 at 3:00 PM | Unregistered CommenterFerdinand Engelbeen


The ice cores CO2 shows the true atmospheric CO2 level of the past, but with averaging, which increases with the time you (can) go back in history. Averaging levels off the variability, but doesn't change the average itself over the period of interest. The remarkable point is that CO2 levels follow the temperature (proxies) quite linear with a ratio of about 8 ppmv/degr.C. That is visible in the Vostok and Dome C ice cores (resolution about 600 years) over the past 800,000 years, but also in the Law Dome ice core (resolution about 40 years) over the past 1,000 years. Only in the past 150 years, we see a sudden increase in CO2 levels which doesn't match the temperature increase...

If the sensitivity of CO2 levels for temperature changes was larger at any point of the past, that would show up in all ice cores, as the interglacials were 5000-15000 years long and the glacial periods around 100,000 years long, far beyond the 600 years resolution of the ice cores.

Aug 5, 2011 at 3:19 PM | Unregistered CommenterFerdinand Engelbeen

The "human fingerprint of Co2" is the declining percentage of C13 in the C13/C12 ratio. But C4 metabolism plants alter that ratio by their preference for C13.

And C4 plants like corn and sugar cane account for 30% of terrestrial carbon fixation.

I don't see how there can be a valid "fingerprint" proving the "excess" of Co2 is manmade ... other than it being the massive increase of man's growing of C4 plants like corn and sugar cane (and a lot of others).

And of course we now have this coming paper showing 80% of "new" Co2 is because of the temperature rise (not the other way around).

This is a horrible blow to AGW.

Aug 5, 2011 at 3:35 PM | Unregistered CommenterBruce

Who'd care to estimate the surface area of the oceans as a source and as a sink. They are pretty crinkly at the best of times.

Aug 5, 2011 at 4:06 PM | Unregistered CommenterAlan Reed

Salby's talk via podcast is sufficient motivation for me to look more into the earth's carbon dynamics prior to his book and paper coming out.

For me that is reason enough to praise Salby's efforts and reason for me to thank him.


Aug 5, 2011 at 4:07 PM | Unregistered CommenterJohn Whitman

Quote, FE, "The ice cores CO2 shows the true atmospheric CO2 level of the past"

If only that was true.

The reality is that CO2 levels found in pre-industrial ice cores have been 'corrected' downwards and spliced with modern direct measurements to create the impression that CO2 levels formed a 'hockey-stick' curve allowing humanity to be blamed.

As Salby pointed out “anyone who thinks the science is settled on this topic, is in Fantasia”.

Aug 5, 2011 at 5:07 PM | Unregistered CommenterMac

I really do not understand why so many people who comment on the podcast are talking about temperature and the levels of Co2 in the atmosphere? Salby tries to explain that temperature and not human produced Co2 is controlling total Co2 emissions. However the emissions are on average totally absorbed by the sinks.
We already know and he does not argue that temperature IS responsible for Co2 levels over the longer term, ie after 800 years.
His point is that human produced Co2 does not correlate with total emissions.

Aug 5, 2011 at 10:33 PM | Unregistered CommenterDung


C4 plants also discriminate between 13C and 12C, but less than C3 plants. While the atmosphere currently is at -8 per mil d13C, C4 plants go down to -15 per mil and C3 plants to -25 per mil. Thus anyway, if there is more plant decay than plant growth, that can't be separated from fossil fuel use. But as the oxygen balance shows a small deficit, the biosphere is a net sink for CO2, and preferentially 12CO2, thus leaving more 13CO2 in the atmosphere. But we see a decline, which can only be caused by fossil fuel burning...

Aug 5, 2011 at 10:50 PM | Unregistered CommenterFerdinand Engelbeen

@ Ferdinand

Interesting posts. The problem though is that if we accept,for the sake of argument, that humans would have to halve emissions to rebalance CO2 - it is simply impossible to achieve this.

There's a taxonomy of scepticism which is broadly either
- AGW isn't happening, or
- CAGW isn't happening, or
- it is but it's good, or
- it's happening but it's unpreventable.

Alarmists have to overturn every such view. It doesn't follow that if the first is refuted, we're all instantly persuaded to squander trillions on managing the sky.

Can you give any examples of how emissions can be reduced by 50% without significant human misery? What analysis has been done that shows the best way to spend trillions is on managing the weather in 100 years' time rather than something else?

That's the argument that matters.

Aug 5, 2011 at 11:09 PM | Unregistered CommenterJustice4Rinka

Sorry to go O/T but this might be of interest and is loosely related.

Viscount Monckton has just appeared on TV here, on TV3's Saturday morning current affairs show, The Nation. I only heard he was here because of another news piece saying every scientist in NZ refused to debate with him, and that's how they started the piece with Monckton - Manning from Wellington had refused to debate him or even appear. So here's how it went.

Monckton was excellent - measured, informative, authoritative and articulate. Sean Plunket - NZ's Paxman - didn't land a blow. Monckton had a reasoned, factual answer for everything. Apart from calling Federated Farmers 'United Farmers' and mispronouncing Whangarei, he was magnificent. Plunket seemed quietly impressed.

Next up, Prof Glenn McGregor of Auckland University, interviewed separately. The chance to diss Monckton and demolish his (seemingly plausible) arguments. Oh no. It didn't go like that at all. McGregor's body language was defensive, he appeared shifty. He couldn't disagree with most of what Monckton said and was played back to him. Plunket looked like he'd got a good fish on the line. McGregor has hesitating, unconvincing and vague. The only factual argument he used was a whopping lie - that if we didnlt introduc ethe ETS, NZ would warm by over 1ºC in the next 25 years (if he's still around, it might be good to revist that with him). Plunket's questions over adaptation vs mitigation, a la Monckton, were met with evasion and bland appeals. The usua guff about 'we're not good enough at communicating...' Hopeless.

No wonder no-one on the warmist side want to debate him. They'd get shredded.

It's not up yet but you might be able to watch it on demand soon:

Aug 6, 2011 at 1:00 AM | Unregistered CommenterGixxerboy

Ferdinand, "But we see a decline, which can only be caused by fossil fuel burning..."

I was sure the exact same thing was said about the C12/C13 ratio.

So I won't take your word for it.

IMHO, every bit of the IPCC argument should be ripped apart and examined, because there is no reason to believe any of it.

Aug 6, 2011 at 3:28 PM | Unregistered CommenterBruce

So, CO2 is "condensable", just like H2O, only the removal from the atmosphere is a bit slower. Finaly the mainstream is catching up.

Aug 7, 2011 at 8:58 AM | Unregistered CommenterEdim


The reality is that CO2 levels found in pre-industrial ice cores have been 'corrected' downwards and spliced with modern direct measurements to create the impression that CO2 levels formed a 'hockey-stick' curve allowing humanity to be blamed.

Ice cores were taken by the Russians, Japanese, French, Americans,... CO2 levels were measured from different cores in very out of different climates with huge differences in core temperature and very different accumulation rates. Despite that, the CO2 levels for the same periods in time are near equal (+/- 3 ppmv).
If there was any "correction", I should expect at least one (retired) person of the hundreds involved to whistleblow such a travesty.

The "splice" has an overlap of 20 years, independently measured in the ice cores and the atmosphere. Which confirms that ice cores show the true CO2 level of the ancient atmosphere.

Aug 7, 2011 at 5:24 PM | Unregistered CommenterFerdinand Engelbeen


- AGW isn't happening:
It is, but far mor moderate than the models imply

- CAGW isn't happening:
Definitely not happening.

- it is but it's good:
A moderate warming is good (especially for my and Bishop Hill's wet and cool climate)...

- it's happening but it's unpreventable.
Why should we try to prevent something beneficial?

Aug 7, 2011 at 5:31 PM | Unregistered CommenterFerdinand Engelbeen

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