For what it's worth, when proxy studies are referred to as authoritative statements, I switch off. Paul Dennis and Alan Kendall have given good arguments for concluding that ice proxies have some value in climate reconstructions but they cannot be used to claim that the temperature in 3000 BC was 20 C. If only treemometrists were so cautious. Calling out Mann, Rahmsdorf, Schmidt

Paul Dennis, Alan Kendall

Fair enough. You are operating way above my level, so further discussion would be a waste of your time.

Are you familiar with the concept of "lies to children"?

When you explain something to a primary school child you give them a very simple version, which they can understand. Secondary school pupils get a more detailed version but still without discussing the uncertainties. A level pupils get more detailed information, more discussion of scientific method and an introduction to the uncertainties.

Undergraduates get more detail and more information on alternative hypotheses.

By the time you start a PhD, you find that Fred thinks this, George believes that and the uncertainties are large enough that they are still arguing about who's right.

The problem on a site like this is to pitch the science at an appropriate level.Too high and you lose everybody, too low and you are patronising. I'm still trying to find the balance, after years arguing the warmist case on sceptic websites.

Witness your 7.47 post, which was probably pitched a bit high. Your point about the inability to rigourously test the CO2 paleoclimate hypotheses is well taken, but applies in all cases where one is restricted to observation rather than direct experiment. I remember that the last time we spoke, you were about to begin a study of an early Antarctic glaciation. Do you find it frustrating that any conclusions you make are ultimately untestable? We all make the best use we can of the evidence available.

Now, if you'll excuse me, I'll go back to arguing with dung.

Dung, I realize that I have not really tried to answer the question you originally posed. So here goes. I don't believe that the geological past provides a definitive answer. It is difficult/impossible to answer many climate cause and effect questions about the present day. So to expect the geological record to provide definitive answers is asking a lot. The record is incomplete and many important parameters are either not preserved or we do not have the wit or skill to disentangle them. As Paul Dennis has just argued, even our previous estimates of palaeotemperatures are unreliable. Consider how difficult it is today to derive a single global estimate of temperature, now consider how much more difficult it is to do this for the past - for a thousand years ago, for amillion years, for tens or hundreds of million years ago. We have no way to get this type of information. Much as I would wish my science could oblige, I do not consider geological evidence is capable of being a slam dunk answer.

That said geological evidence is not powerless. Any climate explanation will have to explain what we do know about past climates.

Dung

This is the reference you asked for. My most recent source on the dynamics of early interglacial warming was Shaking et al (2012).

Abstract and figures here and a discussion at SKS here .

This is the most relevant information.

What's Going On?
What appears to have happened, based on global climate model simulations run by Shakun et al., is not all that different from our previous explanation of the supposed CO2 lag - just a bit more nuanced.

As we already knew, the Earth's orbital cycles trigger the initial warming (starting approximately 19,000 years ago), which is first reflected at the highest latitudes (i.e. Greenland and the Arctic - see "Onset of seesaw" in Figure 4).
This Arctic warming melted large quantities of ice, causing fresh water to flood into the oceans.
This influx of fresh water then disrupted the Atlantic meridional overturning circulation (AMOC), in turn causing a seesawing of heat between the hemispheres. The Southern Hemisphere and its oceans warmed first, starting about 18,000 years ago.
The warming Southern Ocean then released CO2 into the atmosphere starting around 17,500 years ago, which in turn caused the entire planet to warm via the increased greenhouse effect.
In short, the initial warming was indeed triggered by the Milankovitch cycles, and that small amount of orbital cycle-caused warming eventually triggered the CO2 release, which caused most of the glacial-interglacial warming. So while CO2 did lag behind a small initial temperature change (which mostly occurred in the Southern Hemisphere), it led and was the primary driver behind most of the glacial-interglacial warming.

According to the Shakun et al. data, approximately 7% of the overall glacial-interglacial global temperature increase occurred before the CO2 rise, whereas 93% of the global warming followed the CO2 increase.″

Thanks Alan for a properly balanced response in a highly politicised world.

Entropic man, so how is the high CO2 level maintained when temperatures decline? You must be able to explain all parts of a climate cycle, not just part of it.

Looking at the quotation you used I tried to list the number of assumptions/statements that were from my own limited knowledge (its not my specialty) contentious but lost count after 10.

Paul Dennis, dung

I was reading Roger et Al (2006l
.
Figurev2 shows a graph comparing radiative forcing and temperature in the Phanerozoic.

The radiative forcing is a combination of the decreasing CO2 and increasing solar insolation. Together they give a better fit to the changing temperatures than CO2 alone.

I also forgot a one-off effect which brought on the decline in CO2 in the latter Devonian and Carboniferous and contributed to the Carboniferous ice age.Plants invented lignin.

This is stronger than cellulose and allows much bigger plants.It is also much harder to break down. The result was removal of much of the atmospheric CO2 and its accumulation as what became coal seams. This continued until decomposers evolved lignin digestion.

Add a 7th control knob, the biosphere.☺

EM, you will have to give the full reference!

Again you imply you know the temperature throughout the Phanerozoic. Our records are simply not good enough to determine this. I suggest you read up some basic stable isotope geochemistry, check the raw data record of the oxygen isotope composition of carbonates throughout the Phanerozoic, follow the debate on the evolution or not of the oxygen isotope composition of the ocean, try to understand the role of diagenesis in resetting of oxygen isotope compositions realising that much of the Phanerozoic record is based on rocks that have undergone burial and uplift. Then and only then are we in a position to debate the relative merits of the oxygen isotope record of Phanerozoic temperatures.

With 7 control knobs one can create absolutely any trend one wanted to in a model. It doesn't add a scintilla of knowledge to the debate.

With four parameters I can fit an elephant, and with five I can make him wiggle his trunk.

Alan Kendall

Regrettably this is a blog, not a paper. If we put in a full reference list every time, we would be here all day. On a blog like ta more relaxed approach prevails. There is a lot of literature out there on the interaction between climate factors and the uncertainties involved. It does not stop people trying to make sense of it.

Of course it is contentious! It is also important, or we would not be arguing about it.

The nice thing about retirement is that one can put aside some of the professional reticence. I can build a world view using the best fit hypotheses.

For long term paleo that is temperature driven by insolation and CO2. For modern climate it is CO2. If you know of other hypotheses with a better fit to reality and better predictive power, please tell me.

The refernce is "CO2-forced climate thresholds during the Phanerozoic" by Dana L.Royer, published in 2006.

It is available as a PDF from several sources, but I have been unable to set up a working link.

Look particularly at Figure 1d comparing CO2 and temperature, and Figure 2 comparing radiative forcing and temperature.

Entropic man confusion reigns. It wasn't me that requested a reference.

EM, I thought that was the paper you were referring to. However you said the reference was Roger et al. (2006). Okay lets get one thing straight. Figure 1d and Figure 2 do not compare CO2 and temperature and radiative forcing and temperature.

The proxies referred to in Figure 1d and Figure 2 are proxies of atmospheric CO2 levels and not temperature.

I return to my points made earlier. You have a world view and very limited knowledge of the proxy evidence for global temperature and even less knowledge of the details of how these are constructed. You constantly refer to wanting to argue but are not interested in debate or learning because of your entrenched views.

As you so eloquently said yesterday - garbage in, garbage out. Except in thsi case you are providing the garbage.

PD, AK

EM is respected here for his persistence and diligence in studying the science of AGW, and for his moderate and courteous use of language*.

In discussing things with EM, it is helpful to understand some points:

- EM will produce evidence for something he believes. When its pointed out to him that it is vague and inconclusive he will explain that that is because you are demanding unrealistically high standards of evidence.

- EM has faith in the ability of very simple analytic formulas to capture the behaviour of very complicated systems.

- EM will sometimes imagine something and, from that point, state what he has imagined as if it were reality**.

- EM says he attended a course "statistics 101". He tends to belittle the statistical knowledge of people who point out that he computes confidence intervals where the necessary assumptions are plainly wrong.

- EM sincerely believes he is an objective amateur scientist dispassionately seeking the truth as he seeks tirelessly to find evidence to confirm his nightmares of man-made catastrophe.

- EM sometimes comes across as a bit patronising, as if he were addressing a class of 13 year-olds. I ascribe that to a lifetime of addressing classes of 13 year-olds.

But, having said all that, I'll say that BH blog is better for EM's contributions. Just keep your cool when debating with him.

_________________________________________________________________________________________________
* Except sometimes. Such as, for example, when I suggested that since GCMs are programmed to simulate warming due to GHGs, it's not surprising that they predict such warming. He told me this showed I was a senile old fool who believed that there was a conspiracy of scientists going back two hundred years to pervert science.

** Such as when he told me that there are gaps in my knowledge of physics and, as an example, I lacked sufficient knowledge of physics to do O-level specific heat calculations (apparently on the basis that he had never seen me do such calculations).

Royer DL. 2006. CO2-forced climate thresholds during the Phanerozoic. Geochimica et Cosmochimica Acta, 70: 5665-5675.

http://droyer.web.wesleyan.edu/PhanCO2%28GCA%29.pdf

Martin A, I have no problem with EM and amateur scientists and autodidactics in general. After all we are all that to a degree. However EM can be willfully obtuse at times viewing the world from his trench. He does have a knack of appearing to talk down to people and you may be right that it is force of habit having spent a lifetime of teaching 13 year olds.

When given the opportunity of debating with people who know something about the subject he closes down the debate.Witness his comment at 9.49pm where he suggested I was operating at way above his level therefore further discussion on my part would be a waste of my time. If I thought it was a waste of my time I wouldn't be here.

He then comes back having found a paper by Royer (2006) and completely misinterprets two plots. This after I had already indicated several issues with the approach taken by Royer in assessing Earth surface temperatures. He could have engaged with these issues rather than ignoring them. I would have been more temperate in my response if he hadn't put a 'smiley' at the end of his!

He has a genuine opportunity to discuss with someone who has worked for the last 27 years on isotope proxies and currently has several research students working on new estimates of Earth surface temperatures in the Palaeozoic and Neo-Preoterozoic. The conversation as it is is like ships passing in the night on different courses.

He is right. I don't have time or interest for such engagement.

+1 Paul Dennis

Maybe we should be concerned that Dung's original assertion has been so thoroughly debunked. Has he noticed?

Dung,

The problem is that you resist evidence. You are unable to interpret evidence and yet you ignore testimony from the likes of Paul Dennis, who is even handed. You seem to have a theory to which you cling, regardless of evidence.

Paul Dennis

Ouch, my mistake! I will retire and bandage my wounds.

Thank you for the opportunity to engage, but, as we have seen, it would probably not be productive.

The gist of your comments to date is that the uncertainties are so large that one cannot derive useful climate information from palaeontology. Alan Kendall said exactly that to Dung.

Your colleagues regard the data as useful. They are using it to better understand both the pattern of Phanerozoic climate and the driving mechanisms.

As you pointed out, I lack the expertise to debate the technical details and your colleagues have failed to convince you that useful approximate data is available. What can we usefully discuss?

Radical Rodent

At the start of the Holocene temperatures rose 5C in10,000 years. That is 0.16C per 320 years.

Since 1970 temperatures have risen at 0.16C per decade.

The difference between January 2016 and February 2015 was 0.31C. That is 0.16C per fortnight.

How fast do temperatures have to change before you call it rapid?