Dung,

you completely misunderstand my evidence and position. With careful experimentation and measurement it is possible to determine temperature from appropriate proxies. For example, it is my view that the Phanerozoic marine isotope record determined by Veizer and co-workers can be interpreted as a temperature record and this record shows that on the time scale of tens to hundreds of millions of years temperature is decoupled from CO2. However, one must be cognisant of the fact that the interpretation is limited by our lack of understanding of the evolution of ocean oxygen isotope composition through geological time. One must always be open about the limitations and fully aware of the nature of possible errors and their impact on precision and ultimately interpretation of the data.. This is what I have tried to highlight in my posts. Such awareness has been conspicuously absent, or willfully ignored in many studies that combine proxies to produce a long chronology.

New isotopic tools are being developed that hold the promise of a 'thermodynamic' proxy. By that I mean a proxy whose response to temperature can be determined a priori from thermodynamic considerations. Measurement of the proxy value can then be used to estimate temperature much like the thermal expansion of mercury in a thermometer. These techniques are 'orthogonal' to the standard oxygen isotope thermometer and so decouple the temperature estimate from knowledge of the ocean isotope composition.

I see two complementary approaches. The first would be to reproduce the extensive marine oxygen isotope data set for the Phanerozoic. This will allow us to develop a long chronology for Earth's surface temperature. The second would be a series of deductive experiments targeting specific predictions of the current paradigm of a CO2 control knob.

Each would be very major undertakings and require many years, if not tens of years of effort. I'm not sure it would be possible to do on an ad hoc basis. The experiment would require many tens of thousands of measurements at the highest possible precision. It would need dedicated instruments etc. It would need access to, and collection of pristine fossil material with appropriate meta-data. Not with standing these caveats the thought of conducting such a programme regularly interests me. Some attempts have been made over the past few years but the quality of the data has not been sufficient to provide unambiguous interpretations.

Paul Dennis

Sorry, I've been busy.

It will probably remain ambiguous. As a biologist one gets used to complex multifactorial systems and the problems of trying to extract the effect of one factor from all the others. Regrettably one becomes resigned to making the best of it.

On another tack, I was just reading the final version of Hansen et al (2016), download availably here . They make considerable use of Eemion paleo data. I would welcome your opinion of its validity.

The gist is that we can expect a lower rate of warming than the IPCC A1B scenario, but much higher rates of sea level rise.

I tend to think in terms of energy flow, which makes me interested in their reasoning. The key to the authors' projection is a massive increase in the rate of ocean heat uptake by the deep oceans in the latter 21st century as freshwater melt from Greenland and Antarctica disrupt the AMOC. Curiously this produces a big temporary increase in the TOA imbalance and a temporary drop in temperature. The deniers will love it!

One concern.Their models predict South Atlantic cooling and a cold spot off Greenland in 50 years Both are already visible .

Paul Dennis thank you for that expert technical assessment.

The time frame, and likely costs, would exclude such a project from climate science's pressing need, a quick easy win. The fact that a 'win' could not be guaranteed for climate science purposes, probably doesn't help either.

This is not about cherry picking data, but choosing not to plant an unknown cherry tree sapling, in case the eventual fruit, turns out to be unpalatable.

EM, thank you for the link to the Hansen et al paper. I'll certainly look at it but you'll forgive me if it takes a few weeks. It's over 50 pages long. However, having read the abstract I'd say there is nothing really new in it. People have been hypothesing for a long time about freshwater inputs and shutdown of the ocean circulation with consequent effects on ventilation and CO2 levels. People have also been interested for some time in the Eemian as a possible analogue for the present day, especially the end Eemian. We've known that Eemian temperatures have been generally warmer but don't have any degree of precision on how warm. Is it 0.5, 1.0, 1.5, 2 degrees? It is actually very difficult to determine. We have also known that the Eemian climate appears more unstable than our own. Finally there is very good evidence that Eemian sea levels are higher than at present by several metres and that there were periods when tere might have been rapid steps in sea level. Again, as with the temperature the evidence is somewhat ambiguous and difficult to tie down.

So my main concern is that any paper that starts with a premise that fossil fuel usage will lead to catastrophic failure of Greenland and Antarctic ice sheets which is unacceptable to humanity will inevitavbly find evidence that this happened in the Eemian whether it did or not!

However, kudos to the authors who put up front that models are an imperfect representation of the climate system, that paleao and proxy data are riddled with ambiguities and the modern record is too short and imperfect. Nothing has changed with this paper - all three statements are still true and impact our ability to test hypotheses which is where this discussion came in.

I waited for Paul to respond first because its his speciality. I did want to reply earlier because I saw some of you reaching too pessimistic conclusions. I still think Paul is conveying an overly pessimist message. Paul has already mentioned success stories such as the detailed studies of cave speleothems in the Middle East where it can be concluded that most of the isotopic changes are due to a water effect. Surely you should infer from this that it is possible to tease out past environmental parameters. Paul's gripe is with people who don't appreciate the complexities of the proxies they use, but plough on regardless and falsely present temperature data when that may be nothing of the sort.

Some of you have been puzzled by my support of Paul's position while earlier accepting temperature data from ice cores. I'll try to explain. I, and others, use the isotope data as a temperature proxy because we believe the changes reflect temperature and other factors, but (and this is the important point) we believe those other factors are temperature dependent. Thus although absolute temperature values may be exceedingly difficult to obtain (Paul's argument) timed relative temperature changes (when coupled with dating methods on the host ice) are apparent (my argument).

So be more positive Dung, its not as you may have thought.

I am getting the distinct impression that I am playing Watson to Paul's Sherlock, trying to explain his much greater expertise.

Mike Jackson says - "that same "community" are desperate for "a quick, easy win" whether because they genuinely believe that global warming is going to be catastrophic [..]or because they fear it won't be and have their own environmentalist agenda to pursue."

That seems to sum up EM's posture on Climate Change fairly succinctly. He triumphantly brandishes any publication, speculation or rumour that might be interpreted by him to have concluded,suggested, implied or hypothesise that anthropogenic emissions of CO2 are causing unprecedented warming leading inevitably and rapidly to catastdrophe while dismissively rubbishing any research conclusions, climatic,paleoclimatic data or evidence that do not support his views and thus offend his deeply held convictions of impending disaster.

This posture reminds me of the reported behaviour of 17th century witch hunters.

Mike Jackson, spectator

I would love to be wrong!

Show me convincing evidence that my fears are groundless and I will stop worrying.

Note that "convincing" refers to high quality peer reviewed papers in reputable journals which agree with observed data and known physics, not posts on sceptic propaganda sites or dubious papers in attack journals. I was never very good at wishful thinking.

Unfortunately the output from the climate datasets and the published literature show that AR5 is probably conservative. As more research comes in the prospect is looking worse, rather than better.

Alan Kendall

I do not think you need excessive vulcanism to end a snowball Earth episode.
The onset of Snowball conditions tends to coincide with mountain building episodes and accelerated weathering, or with the appearance of photosynthetic organisms. Both produce a drawdown of CO2 to very low levels, followed by worldwide glaciation.

Once glaciated a snowball Earth has very little weathering, so drawdown of CO2 stops. Normal levels of vulcanism are enough to increase CO2 over millions of years. When the CO2 concentration is high enough to start tropical thawing the positive feedback loop of reducing ice albedo does the rest.

Paul Dennis

Many thanks for the comments on Hansen et Al (2016)

So my main concern is that any paper that starts with a premise that fossil fuel usage will lead to catastrophic failure of Greenland and Antarctic ice sheets which is unacceptable to humanity will inevitavbly find evidence that this happened in the Eemian whether it did or not!

This is always the scientist's dilemma. If the science suggest that there is a problem, do you become an advocate for its solution?

If you do advocate, subsequent work becaumes automatically suspect as you describe.

If you do not advocate, the problem may not be addressed.

I vaguely remember lines from "Day afterTomorrow"

Politician-You should stick to the science and leave policy to us.

Scientist-We tried that and it didn't work.

As an active climate scientist, do you feel that you should not take part in the policy debate?

If I became an active scientist again, should I stop posting comments at BH, ATTP or wherever?

Sorry Entropic man, increased volcanism not my idea. I was just quoting other people's ideas.

Don't much fancy yours either. Seem to remember snow, and eventually ice, absorbs more CO2 than warmer water. So what stops continual CO2 removal? If volcanism built up CO2 over millions of years, then some lava and pyroclastic deposites would have come to rest directly on ice. Where is the evidence for this? I would expect to find these materials to show collapse features. I don't know of any such occurrences. The only part of "your " explanation I would unreservedly accept is the effect of decreasing albedo as ice cover declined. My own guess about snowball earth is that either the sun hiccuped, or the solar system passed through a dust cloud. Nothing to do with CO2.

Completely off topic but I thought you might enjoy this. My wife just told me that our 15-year old granddaughter, who lives with us, looked over my shoulder as I was reading this thread and saw a posting that thanked me by name for my contributions. Later she expressed concern that "grandad is being groomed".

The mind boggles, I'm sure golfCharlie can have great sport with this.

Paul Dennis and Alan Kendall, thank you again, for your expertise and insight.

It again reminds me of some of the miscarriages of justice, exposed years after the trial. The police 'believed' they knew who the guilty party was, and then had to 'find' evidence to fit. Some members of the public have proved vulnerable to suggestions about changing the slant of their evidence, some paid professional experts have been relaxed about finding the correct evidence, and ignoring that which conflicts.

It is good to know that experts are still able to report on the evidence they have, rather than 'best fitting' it to a a predetermined verdict. In my cynical experience, they are more trustworthy!