Martin A, I tried to explain in the paper that the model I gave was only a first order approximation and was not suitable for quantative analysis, just to illustrate the most basic behaviour of the carbon cycle. The linear model that I used is not immensley better than one that goes through the origin, but it *is* better and the confidence interval on the adjustment time includes the uncertainty due to estimating the offset parameter. More importantly, if the line went through the origin, that would imply that the difference between natural emissions and natural uptake would be zero if the atmosphere had zero CO2, however Henry's law means that this could only be true if the oceans were also carbon free. The bias term is therefore fully justified on the grounds of physical plausibility.

Hope this helps (I am very pleased to hear someone has actually read the paper!)

“At the end of the day, any argument that suggests that the rise in CO2 is natural needs to be able to explain why the observed annual rise in atmospheric CO2 is less than annual anthropogenic emissions (on average about half). If the oceans and terrestrial biosphere were a net carbon source (taking in less than they emit) atmospheric CO2 would be rising faster than the rate of anthropogenic emissions as both mankind and nature would be net sources. ”

This is can be refuted with a relatively simple 'bath-tub' experiment.

A large bath-tub (with some level of water in it) has a large running tap at one end and a similarly capacious plughole at the other end. The tap is pouring water (imagine CO2) in at a slightly faster rate than it is disappearing down the plughole. So the level in the bath is rising. Take a jug of water (imagine it as containing a red dye, to help with the visualisation) and pour it into the bath. What happens?

The level in the bath will continue rising at least as fast as before and possibly faster, but how much? That will depend on how fast you pour, and WHERE. It is in fact quite possible to pour directly into the vortex at the sink and the bath water will not turn even slightly pink. The rate of increase of the water level would be similarly undisturbed. You can, of course, pour somewhere else and get a different result.

The concept of CO2 as being “well mixed” is an assumption that is misleadingly wrong in many situations. Natural CO2 sources and sinks are (by definition) not at equilibrium with either each other or the atmosphere. They are not even at a steady state. Henry's Law is a statement assuming equilibrium.

"If the oceans and terrestrial biosphere were a net carbon source (taking in less than they emit) atmospheric CO2 would be rising faster than the rate of anthropogenic emissions as both mankind and nature would be net sources."

- Dikran, this is quite simply a non-sequitur, as in - it does not follow.

Katabasis - for the benefit of the slower witted members of the congregation (such as me) would you please spell out why this does not follow?

Because if you accept the it does follow then you have to accept that what Salby says in bunkum. But Salby can't be wrong, and therefore the sentence must be a non-sequitur.

Chandra - stop being so silly. Please.

Big Oil -

Because the global total of ((natural sources + anthro sources) - natural sinks) could come in at any rate of increase (or decrease). My understanding, especially after seeing Salby speak, is that the natural cycles completely overwhelm the anthro output and therefore variations in natural sources vs sinks are far, far more significant than relatively tiny increases in anthro output.

Dikran on the other hand presents us with an argument presupposing that the anthro contribution overwhelms the fluctuation in natural sources / sinks.

Katabasis, you ignore the word 'net'. In other words, the natural flows might be hugely bigger than the unnatural ones but only the net value is important, the net being what is left once you have subtracted the flows out of the sources and into the sinks. This net value would be zero for a system in equilibrium. Compared to zero, anthro flows are huge. And atmospheric CO2 is rising at half the anthro flow rate. Therefore the natural world is absorbing half of that flow.

-Humans are emitting more than enough CO2 to explain the rise
-CO2 rise has accelerated in lockstep with the rise in human emissions. Hasn't followed any natural cycle
-Other gases are curving upwards too, due to human activity
-The ice core record shows the recent CO2 level is unprecedented for thousands of years and so indicates the cause is man

The evidence is overwhelming that man is the cause is it not? To come up with some fabulous reason why the human CO2 emissions is magiced away is one thing, but to also have to find fabulous excuses to dismiss the ice core record and to dismiss the rise in other gases, well it's just too much. Salby would be more convincing arguing the world was flat.

Big Oil, my post at Nov 13, 2013 at 6:50 PM , just before, Katabasis' comment was in fact an attempt to demonstrate how Dikran Marsupial's argument falls down, using the flow of water in and out of a bath as an analogy for carbon dioxide.

Maybe I failed! I could use other analogies. Try imagining the rise and fall of water levels in a tidal estuary (where the tide represents natural carbon dioxide fluxes, and the river represents human contributions). The river flow has some effect on the observed water level, depending on the time of day, and where the observer is standing. But it is not sensible to assert that it is the controlling influence on sea level.

MartinA For Salby's hypothesis to be viable, he would need to be able to explain how the natural environment can be causing the increase in atmospheric CO2 whilst being a net carbon sink, that is taking more CO2 out of the atmosphere each year than it puts in. This can be determined with high reliability using the assumption of conservation of mass and the measurements from Mauna Loa and records of fossil feul use. Prof Salby himself presents the basic equation needed in his Sydney Institute talk, and also explicitly states that the two sources of data required are reliable. For further details, see my article at skeptical science http://www.skepticalscience.com/salby_correlation_conundrum.html .

MartinA, interested to learn your thought on this matter, but I don't agree with everything Murray Salby says, unless I have misunderstood him. I would prefer that he said that the ice-core record COULD be hiding far larger swings in the atmospheric CO2 record, not that they must be.

This is the usual point every time a new hockey-stick is presented, with high short-term changes presented against a background of historical data that is simply not able to measure short-term changes as they occurred at the time. The asymmetry of the scientific method is also such that members of the hockey-team can present their latest stick as being "unprecedented" but the sceptical retort is merely that "It could be, but the data doesn't allow you to draw that conclusion".

As an aside, yes, it is difficult for a sceptic to improve the perceived quality of that objection in the face of the so called "precautionary-principle" which weighs so heavily in so many minds.

But asymmetry works in favour of sceptical viewpoints when cAGW proponents complain that sceptics use many and varied objections to their grand synthesis, some of them probably/possibly wrong. What the BBC et. al. routinely fail to grasp is that, as people often like to quote Einstein as saying, only one of the objections needs to be correct for the grand synthesis to be falsified.

MA, I'd say it was more than just "plausible", I don't think anyone seriously doubts that the carbon cycle is a closed system and that carbon is not spontaneously created or destroyed or leaves the earth in any significant quantities. Prof. Salby certainly doesn't doubt it, given his Sydney Institute talk. Likewise nobody seriously doubts the modern instrumental CO2 record (ISTR WUWT ran a very good article on why Mauna Loa is actually quite a good place to measure background CO2, despite being a volcano), nor the estimates of fossil fuel use as governments keep good records on that as it is an important element of trade and taxation. The error bars on the data are much too small for there to be any real doubt about the conclusion. And that is only one line of evidence, there are many others http://www.skepticalscience.com/anthrocarbon-brief.html .

Martin A> I had no difficulty quickly and easily reproducing Salby's graphs, in the cases I tried, from publicly available data

You certainly can't do that for the ones I was talking about, because he has made up some key parameters and not told us the values. As I said.

If you know those values, then do please tell us what the values are for the non-conservative processes in the ice, and the diffusion in the ice. Because Salby certainly doesn't.

MartinA, so you didn't actually reproduce anything that involved diffusion in ice. Or did I get you wrong?

But don't hold your breath waiting for that paper. He's not going to publish anything. If he were interested in doing so he would be interacting with scientists, who understand what he is talking about, rather than giving lectures to the public and politicians, who don't.

CO2 has curved upwards.

The Law Dome ice core curves upwards at the end too, and that ice core has decadal resolution.

Other gases like CFCs, SF4 and nitrous oxide have curved upwards due to human emissions, in line with those emissions.

CO2 curves upwards, doesn't follow any natural cycle.

Besides if Salby thinks CO2 follows temperature and CO2 is a proxy for temperature then it looks like temperature has accelerated in the past decade. No pause.

And if the ice cores are all wrong, why are skeptics citing them as evidence of some kind of lag between CO2 and temperature? Either the ice cores are wrong because of diffusion of gases, or they are right and highly accurate enough to determine small lags.

The contradictions here and avoidance of the strong evdience that the CO2 rise is human caused are evidence that Salby's position is incoherent and nuts.