Basically, carbon saying sounds like it is counting tree rings:
"Since the 1960s, researchers have mainly done this recalibration with trees, counting annual rings to get calendar dates and matching those with measured radiocarbon dates. The oldest single tree for which this has been done, a bristlecone pine from California, was about 5,000 years old. By matching up the relative widths of rings from one tree to another, including from bogs and historic buildings, the tree record has now been pushed back to 13,910 years ago."
One question, how are they able to push trees ring counting back 13,910 years, if the oldest tree they have counted was 5000 years old. The limit is 5000, right?
And another question, why was this tree only "about 5,000 years old"? They have the very tree, it is either possible to count the rings or not... So why are they rounding (up or down)?
> By matching up the relative widths of rings from one tree to another, including from bogs and historic buildings, the tree record has now been pushed back to 13,910 years ago."
This is exactly how they did it.
edit: Imagine I have one 50 year old tree in the yard, and a house with a log in it that was cut 40 years ago from another 50 year old tree. They were both alive at the same time for 10 years. The relative thicknesses of the rings will match for the first 10 years of the tree and the yard and for the last 10 years of the log in the house, giving me a 90 year record.
Yes, of course it is subject to interpretation, but it is not the only source of truth.
And no we don't have a vast quantity of 10,00 years trees but enough to be meaningful. We are not measuring in very precise years the further back we go.
I wouldn't suppose that's meant to be taken personal.
It would be highly pretentious, I think you agree, if it were a normative standard. That's not the case, so it seems they got carried away in trying to be witty
It's a personal peeve, but I find the footnote style of putting in links, rather than inline like the web was intended, to be not only hard to read, but quite pretentious.
These are comments on some web resource, not research papers.
I'd much rather read [1] than [2]. Too much bouncing around; I'm not even sure if it's worse when the text is large compared to the research paper citations, or small.
HN doesn't allow inline links like the web intended. So you either get footnote style or the raw link text (possibly with non-human-interpretable query parameters), and either way is hard to read and interrupts the flow of the text.
These curves are still somewhat fragile. I remember reading that the air polution is difficult to predict, so there are big error margins and further updates keep being worked on.
Does anyone else feel that the understanding of historic levels of atmospheric carbon are based on an set of assumptions that are bordering on farcical in the amount of guesswork they require?
You do know that atmospheric carbon level estimation is completely orthogonal to carbon dating, yes?
Carbon dating is about matching radioactive carbon contents in organic matter to samples from trees or other known-age organic matter. As such, it has a limit of ~50,000 years ago.
Historic levels of atmospheric CO2 is mainly based on samples of gas trapped in ice sheets, or estimates based on carbon quantity in mineral sediments that would have absorbed atmospheric carbon in their formation. As such, estimates go back to the entire history of the Earth.
Especially for recent history, where we have bubbles of air from those times still trapped in Antarctic ice, I see this is a remarkably direct measurement, the very opposite of a "farcical amount of guesswork". If we're talking about 1 billion years ago, I start to agree with you a little more.
but what if there was a time when the ice in Antarctica melt? wouldn't it mean that we don't know when and how long it happened and anything about it's atmospheric contents
The temperatures required to melt the ice in a short timespan, and then the temperatures required to re-freeze it in a short timespan after that, would leave marks in other places in the world as well.
We also know for sure that such extreme events have not happened in recorded history, so at the very least you can trust the method for atmospheric carbon content in the last few thousand years - more than enough to prove man-made as the only explanation of these carbon levels, and to compare for climate effects.
Atmospheric carbon levels are irrelevant to this. C14 date calibration is about the *ratio* of C14 to C12 and C13, not the absolute quantity. Biological processes to not meaningfully select between the isotopes of carbon, anything that grows while exposed to the atmosphere will contain carbon in the same ratio as the atmosphere--but over time the C14 decays, the ratio shifts. That tells you how long since it grew.
(Note the "exposed to the atmosphere" provision--one of the arguments the creationists love is to cite some examples of living organisms that date old. They didn't run the test for giggles, but rather to examine the environment in which the organism was found. Pull something out of a deep cave, date it and you now know how fast the air is exchanged between that location and surface atmosphere. This is because virtually all C14 is created by high energy particles hitting the upper atmosphere.)
Yes, I do too. But I also think that’s true for a lot in science. But try and dare scientific “discoveries” in most circles…
I guess it’s also the media’s fault, which cannot properly report on scientific papers. For example, probabilities become factual statements. Because it sells better like this.
"Since the 1960s, researchers have mainly done this recalibration with trees, counting annual rings to get calendar dates and matching those with measured radiocarbon dates. The oldest single tree for which this has been done, a bristlecone pine from California, was about 5,000 years old. By matching up the relative widths of rings from one tree to another, including from bogs and historic buildings, the tree record has now been pushed back to 13,910 years ago."
One question, how are they able to push trees ring counting back 13,910 years, if the oldest tree they have counted was 5000 years old. The limit is 5000, right?
And another question, why was this tree only "about 5,000 years old"? They have the very tree, it is either possible to count the rings or not... So why are they rounding (up or down)?