An "accusing finger"? In what way?

Not sure why you think that, Dung. While I agree it is so obvious to many that it does't seem to even need mentioning, other people do point out some aspects of it pretty much every day.

If one says exactly the same thing everyday, then you end up boring people in the manner of Doug Cotton or the BBC green-crew.

I don't know what 100 million year period that was, but can you say how solar and orbital conditions differed then from now? If not any conclusions you reach are invalid.

The Devonian seems to have had CO2 levels of around 2000 so we'd expect temperatures to be higher than now, other things equal. The sun would have been cooler then, I think, gradually warming (from memory). I don't know about the orbit. The organization of continents was also different. But these things do vary over such large timescales, so to look briefly at one or two numbers and draw firm conclusions is unreliable.

Dung

You are presumably looking at graphs of temperature, CO2 and solar insolation over the last 500 million years. Please provide links so that we can see what you are discussing.

Dung

Let's try some science.

From Wikipedia I got the following figures

Mean temperature 20C (6C warmer than the 20th century)

Mean CO2 2200ppm

IIRC solar insolation increased at 1%/50 million years, so would be 8% lower in the Devonian, 400 million years ago.

I am assuming a climate sensitivity of 3.0 and forcing of 3.7W/C

Using the empirical CO2 forcing equation the temperature difference between the present and the Devonian would be

5.35!n(2200/335)0)3/3.7=8.2C

Correcting for 8% lower insolation that would be a difference of 8.2*0.92=7.2C.

That is a bit warmer the quoted figure, but within the probable uncertainty. I do not see why you are unhappy.

If you are worried about the lag between the drop in CO2 at the end of the Devonian and the drop in temperature, it is an artefact of the poor time resolution of the Smithsonian graph.

When you use a higher resolution graph the lag disappears, both the temperature and CO2 rise and fall together.

Dung

I know you are not a scientist, but since you are trying to run a seminar on the paleo data, you might want to know a few conventions.

1) Make all the supporting evidence available at the start The rest of us missed Patrick Moore's speech, nor have we visited the Smithsonian or seen your graph. Provide links.

2) Don't just ask rhetorical questions like "How do you explain what happened at the end of the Devonian?" Explain clearly what you think happened at the end of the Devonian, and how your evidence supports it.
If you think that the conventional science is wrong, explain what the science would have expected and how your interpretation differs.

3) Once the debate is under way, go for the ball rather than the man. Argue the evidence rather than get involved in insults. If you think there is a problem with evidence from someone else, explain why.Feel free to introduce new evidence, but provide links so that we can all see it

I have been distracted temporarily by the discovery of an important graph that has been (it seems to me) massively tampered with by Google.

https://xkcd.com/386/

Late to this discussion, sorry. What I find perplexing is the fact that certain well known geologists support AGW. I do not understand how anyone with knowledge of the overall long term climatic stability of the Earth since the Cambrian can entertain views that the present day.climate is so fragile. Belief that human activities are so significant is just hubris.

With respect to the ice core record, this was once one of the key planks supporting AGW, now it can be used to demonstrate how ill founded that support was. Temperature rises before CO2, but more significant to me is that temperature declines for a much longer interval before CO2 declines. This suggests the relative ineffectiveness of CO2 as a climate driver. I don't recall an adequate response of this by the pro-AGW crowd. Perhaps this argument should be repeated ad nauseam until such a response is forthcoming.

Alan Kendall

The default pattern for the last 2 million years has been that Milankovich cycles drive Northern Hemisphere temperatures and CO2 follows, acting as an amplifying feedback. In this cycle temperature drives CO2. Temperature is the forcing and CO2 the feedback.

There is nothing in the physics to preclude the possibility that an increase in CO2 can drive temperature. There is exidence that this happened at the end of Snowball Earth episodes. It is a candidate cause for the Permian extinction and PETM, and is driving the current warming. Today CO2 is the forcing and temperature is the feedback.

Entropicman. No, it has been speculated that volcanism released sufficient CO2 to offset the positive feedback that a totally Ice covered Earth would experience. The explanation has little/no supporting e evidence and is only considered because no better explanation seems to have been proposed (i.e. it is.considered scientifically "true"until more evidence is available). Where is the supporting evidence - lack of volcanic activity that allowed the snowball earth to form in the first place, increased activity at precisely the right time?. How to explain how increasing CO2 (given the decreasing effect this has) could have this effect.

To argue that we can use the far distant past as evidence (where precise timing and environmental reconstructions are so much more difficult to establish) is, in my opinion rather foolhardy. Why do people do it - perhaps because geologists want to demonstrate that there subject is relevant, perhaps because geological departments saw that their students were becoming less employable and jumped on the environmental bandwagon, perhaps because the climate gravy train was just too tempting

Dung

. The scientific method requires only one experiment/observation which falsifies a theory in order for it to be disproved.

Regrettably, reality is rather more comp!ex.

For example, your Devonian claim that temperature dropped before CO2 was based on a poor quality graph and turned out to be wrong. When better data became available,t turned out that they dropped together.

Garbage in, garbage out.

The climate imperialists reject any evidence that does support their alarmist claims.

Entropy man, I think that your last post illustrates one of the points I made - that is difficult to resolve cause and effect problems in "deep time". Commonly the time resolution is not sufficient.

Regarding Milancovitch cycles and CO2 amplification, firstly it is not commonly known that the theory still has problems (as a brief trip to Wikipedia will reveal). The original link with iceages only explained glaciation in alternating hemispheres, but this problem was overwhelmed by the correlation in newly obtained deep sea cores between temperature changes and calculated M cycles. Secondly, although the lag between CO2 and temperature rises might be explicable by amplification, if you adopt this, you have a real problem explaining how the high CO2 amplification, when the temperatures began to fall (due to Milankovitch effects), was unable to prevent that temperature fall and was unable to do this for thousands of years. If there was any CO2 amplification during the temperature declines it must have been a very weak one. If it was weak during declines, why should it be strong during temperature increases? The amplification hypothesis (for that is all it is) has real problems.