h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

- Is (relative) depth the only way that ice cores can be dated?

Nice question Rod!

The evidence for man-made rapid climate change is complicated and clearly not just based on ice cores. It is very hard for your average punter to draw any meaningful conclusions from the mass of complicated evidence, which is why we trust those in the know to draw those conclusions for us.

Unfortunately, if you're making a mass-market propaganda film, it's a lot easier to make your point by presenting one single piece of evidence - something that Joe Public can understand - as if it was conclusive in itself. Picking on a single study that supports your own agenda is the approach usually taken by climate change deniers, which is, sadly, why so many people are convinced by them.

In carbon dating, dating of the age of rocks and in ice core dating there must be a clear set of cross references of known age otherwise you have no clue as to the precise age of any of these things.
I.e. there must be a calibration of some kind.

I don't know the precise details of how ice core dates are cross referenced but, if I recall correctly, the more recent atmospheric conditions gleaned from trapped gases in ice cores correlates very nicely with data gained from tree cross sections (by examination of the growth rings). This can provide a cross reference for up to a thousand years say.

Presumably there are other cross references that can be used to match data data in earlier sections also and then one can be reasonably safe in the assumption that the cross section in between each calibration point is continous and reasonably linear in terms of growth (bearing in mind that is an assumption in caculation of error).

Assuming for one moment that there is say a time in the core when no snow fell and the entire ice sheet only partially melted. Would there not be a sudden jump in the data at this point - i.e. atmospheric gases would change in concentration all of a sudden rather than contnously varying as they normally do presumably?
If such sudden jumps in data are not there then I would guess the assumption that the data are continous is even more safe.
I think it would stretch credulity that such a gap in the data would not be accompanied by a sudden change in atmospheric conditions as it's extremely unlikely that the conditions upon ice-melting and then on re-freezing would be identical so as to mask such a gap.

I remember reading a book on the very subject of ice cores and previous climate change not long ago. Unfortunately I can't remember much of it. 'The Two Mile Time Machine' was the title.

I'm going to a public lecture on climate change this afternoon. Will report back anything relevant.

Aa quick google has revealed to me that the CO2 in ice cores can be radiocarbon dated. So there is one excellent approach to dating the cores.

The limit of carbon dating is around 60,000 years so that's another method of cross referencing the age of ice core layers.

The more methods of cross reference one has then the more accurately we can determing their age.

I like words like unlikely, and assumed errors it allows for uncertainty and the Improbability drive, chaos etc. I just think that if we were 100% certain of our past then we could also be 100% certain of our future, and we'd have a doomsday scenario. Then god help us!
But then he'll be out of the picture by then, probably.

Thanks doc.

Orcus, you've told me pretty much what I was hoping, thank you:

BTW I have the idea that tree ageing can go quite a lot further back than 1,000 years, by overlapping, eg, petrified logs.
Ah, yes - http://sonic.net/bristlecone/dendro.html
"...The bristlecone pine chronology in the White Mountains currently extends back almost 9,000 years continuously ... The hope is to push the date back to at least 8,000 BC. This will be important as the last Ice Age ended about 10,000 years ago"

This business of possibly a surface-melted icecap then: one would expect some kind of disjoint in the record if it had lasted for...? (centuries / millennia?)

From what I've learned here (so far), your post 44, last 2 paras is looking good.

Orcus, where did you find the bit on Radio carbon dating, When I were a lad at school, which was a long time ago.
Carbon Dating was limitted to organic matter, i.e. we could only find out when something was last alive. Apparently being alive causes some depletion of the Carbon Isotopes, or somink!
They might well have revised the method by now and sorted some new method out, but I wouldn't mind taking a look!

http://www.google.com/search?client=safari&rls=en-us&q=calibration+of+ice+core+logs&ie=UTF-8&oe=UTF-8

That was the google search I did, I think the second hit down was my source.

To be fair, you have a good point but I suspect it can be used when the atmospheric 14-C CO2 is trapped in ice and thus cannot equilibrate with atmospheric CO2 and thus can decay as with organic matter.
Having said that, I'm glad you challenged that as it's inspired further reading by me this morning and it seems that 14-C dating isn't really a generally used method for ice-core dating.

I'm afraid that the link blinded me a bit with science, good read though. Maybe with a bit more effort I could understand it all but it gets very wordy and expects us to know all about previous research by the reference to their work.
They seem to mention the limitations of the information quite a lot, and it sounds like they are going to start using the ice core logs for callibration of Carbon dating. It all seems a bit far fetched for me, to think some day, people will just skip this talk about the limitations of readings and just accept what they are told as gospel.

Hmmm sounds familiar.

Now hear the Gospel according to {such and such scientist}.

Don't panic all Orcs were once Elves.....

I have just been directed to the following article,

http://www-pord.ucsd.edu/~sgille/stpa35/petition_justification.pdf

It's a bit long and detailed but basically it begs the question why are we worried about increased CO2, in fact it more or less says that we shouldn't be bothered about it, cause it is not the cause of climate change. Something similar has apparently been published in the Journal of American Physicians and Surgeons (2007).

It is no wonder that the US then are not with us on reducing Carbon emissions.

What is the goal then of Environmentalist propoganda, or even what is the goal of this article.

It might be just as simple as the fact that most of the subscibers to that American Journal are in the pay of the big Pharmacutrical Companies and these are now joining forces with the people that benefit from more oil sales.

Do you go to a climatologist for chest pains?

Then why would you ask a surgeon about climate change?

Good one, I don't suppose you would ask a climatologist about chest pains. But the real question is are you more likely to do something that some scientists say than your own family doctor?

Most Americans trust what their doctors tell them. Suppose it's not just limited to Americans either. We shouldn't underestimate the effect of the medical profession, they wield a great amount of power.

And those at the top of the power tree know it!

Given my experience with doctors badly screwing up my diagnoses, and the fact that I'm a scientist, guess what my answer is?

Arnie,

Don't Panic mate I am inclined to agree with you, I am also none too pleased with diagnoses by my doctor a lot of the time, but being of a scientific mind you know that you and I are not in the majority are we?
Even in this country a lot of people slate environmental pressure groups, "fortunately" over here the environment lobby appear have the ear of the press and have seemingly won the hearts and minds of our government. The same can not be said of the US government.

What to do about it, I don't know.