[alancalverd]

Here's the Vostok ice core  data that makes me skeptical
The timescale reads from left to right and three features are strikingly clear

The temperature rises are very steep compared with the asymptotic falls, indicating a positive feedback mechanism in play
The temperature curve always leads the CO2 curve, implying that CO2 is an effect, not a cause.
The most recent feature shows a continuous steep rise in temperature beginning 25,000 years ago, with a few hiccups in the last 5000 years or so. On a geological scale, it is no different from previous steep rises.

These curves were published in the 2001 "Summary Report for Policymakers" of the IPCC but the anomalies were not highlighted or explained. I attended one of the early presentations of that report and quickly lost confidence in it as John Houghton (editor) introduced himself as a "committed Christian". I'm very wary of people who parade prejudice and superstition as a virtue: science isn't like that.

Moderator's note: This thread about interpreting historical ice cores was split off from "How could you stop the earth's poles from warming?", which is more forward-looking and action-oriented.
- Please post comments in the appropriate thread.

[Bored chemist]

Since we are talking about anthropogenic warming due to CO2, perhaps you could help us out by shading the part of that graph which happened since the first oil well was drilled (August 27, 1859).
( you might need a rather fine nib)
I prefer this chart.
https://xkcd.com/1732/
if you scroll to the bottom you will see what

The temperature rises are very steep

means.

[alancalverd]

No, you can see what a computer model of the future suggests. This is quite different from the facts of the past and depends on a fundamental assumption that is not supported by said facts.

Lots of people are indeed talking about anthropogenic warming due to CO2, but a hypothesis based on a little recent correlation, that is not consistent with 400,000 years of coarse prior data, or explanatory of the cyclic fine structure of the Mauna Loa data, or the discovery of 500-year-old vegetation under a retreating glacier, doesn't fit into most people's definition of science. 

"The last temptation is the greatest treason - to do the right deed for the wrong reason". T S Eliot.  Not my favorite pseud by any means, but everyone is allowed to express one great truth!

[Bored chemist]

No, you can see a computer model of the future suggests.

The bit up to 2016 is real data, not prediction; and it's steep.

[Bored chemist]

a hypothesis based on a little recent correlation, that is not consistent with 400,000 years of coarse prior data, or explanatory of the cyclic fine structure of the Mauna Loa data, or the discovery of 500-year-old vegetation under a retreating glacier, doesn't fit into most people's definition of science. 

What about a hypothesis based on the infrared  absorption of CO2?

What you need to explain is how CO2 doesn't increase warming, when the science says it should.

[Petrochemicals]

Warm and moist conditions obviously speeds decay, peat bogs and tundra emmit alot of the green house gasses, it could just be an effect.

[alancalverd]

The bit up to 2016 is real data, not prediction; and it's steep.

Only a fool would pretend that climate doesn't change, and change quickly from time to time. Curious people might investigate an apparent correlation, but only a True Believer considers unidirectional correlation to be proof of causation.

Of course any gas increases warming, but since CO2 has always followed the temperature curve instead of leading it, and maximises on the Mauna Loa  data in summer (when anthropogenic CO2 emission is least), how can anyone say it is the primary cause? On my planet, causes precede effects.

Just for a change, I concur with Petrochemicals (pity about the name!). What makes sense in my book is the effect of temperature on the activity of bacteria, fungi and coldblooded animals, which convert plant material into CO2 and both eat, and reproduce more, at higher temperatures. So after a sharp temperature rise you will see an increase in CO2 levels which persists with a lag (due to the increased population of said bugs) as the temperature decreases. 

This nicely explains the Mauna Loa and the historic ice core anomalies.

[Petrochemicals]

https://www.iucn.org/resources/issues-briefs/peatlands-and-climate-change#:~:text=Peatlands%20are%20the%20largest%20natural,types%20in%20the%20world%20combined.

There is alot of peat in the North tundra.

[evan_au]

The temperature curve always leads the CO2 curve, implying that CO2 is an effect, not a cause.

The air bubbles trapped by ice are always deemed to be younger than the ice owing to the time lag between snow falling and it being compacted to form ice. In Vostok, the time lag between snow falling and ice trapping air varies between 2000 and 6500 years. There is therefore a substantial correction applied to bring the gas ages in alignment with the ice ages

It seems that it is well-accepted that there is a time difference between the two measures, which must be calibrated out.
- There is likely to be arguments about how to account for this difference.

If I read him right, Euan Mearns is skeptical that humans are causing temperature rise today because they didn't 100,000 to 400,000 years ago. See blog (not peer-reviewed):
http://euanmearns.com/the-vostok-ice-core-temperature-co2-and-ch4/

[evan_au]

Moderator's note: This thread about interpreting historical ice cores was split off from "How could you stop the earth's poles from warming?", which is based on current climate modeling, and is more forward-looking and action-oriented.
- Please post comments in the appropriate thread.

[Bored chemist]

Of course any gas increases warming

Can you explain the mechanisms for argon, oxygen and nitrogen please.

[chiralSPO]

Ok Alan, let's say that you are correct that temperatures have increased before atmospheric CO₂ levels over the course of history before the 1800s. This would make some sense, because we know of several mechanisms by which warmer climates would lead to more CO₂ in the atmosphere (greater temperatures lead to decreased solubility in water, increased rate of wildfires, etc.).

The problem is that this historical data might not be a valid model for the last 250 years or so. If I understand correctly, for most of the history of our ice cores, nobody was excavating or extracting fossil fuels from deep below the surface, and burning them, at a rate of tens of billions of tons (10¹³ kg) of CO₂ per year. It seems quite possible to me that this is unprecedented, and could be a significant departure from historical data.

[chiralSPO]

Of course any gas increases warming

Can you explain the mechanisms for argon, oxygen and nitrogen please.

I saw that as well.

[Bored chemist]

What you need STILL to explain is how CO2 doesn't increase warming, when the science says it should.

[alancalverd]

Of course any gas increases warming

Can you explain the mechanisms for argon, oxygen and nitrogen please.

They are all insulators.

 https://upload.wikimedia.org/wikipedia/commons/7/7c/Atmospheric_Transmission.png shows the oxygen absorption spectrum and also the dominance of water.

[alancalverd]

The problem is that this historical data might not be a valid model for the last 250 years or so.

Admittedly so, but any valid model must explain

the CO2 lag, both long term as  shown in the ice cores and short term as shown at Mauna Loa

the steep and remarkably periodic historic temperature rise and slow fall, that was clearly not due to CO2

and if we reduce anthropgenic CO2 emission, the temperature must fall by a predicted amount in a predicted time to validate the hypothesis.

Which is why I proposed a zero-cost, reversible and negligible-impact method of reducing anthropogenic CO2 by 25% in about 5 years, several years ago. So far, nobody has dared to do the experiment. So either the climate crisis isn't that acute, or the hypothesis is known to be weak. My own opinion is that the crisis is a lot worse than any politician dares to imagine, and praying to the CO2 gods won't avert it. But five years is a lifetime in politics. 

[alancalverd]

What you need STILL to explain is how CO2 doesn't increase warming, when the science says it should.

I never said it didn't. A squashed fly on my windscreen slows the car down, but that's no reason to ignore the binding brakes.

[Bored chemist]

Of course any gas increases warming

Can you explain the mechanisms for argon, oxygen and nitrogen please.

They are all insulators.

You mean that, if you get a big ball of rock, and enclose it in an insulator which allows radiation through from the Sun, the ball gets hotter- a bit like... a greenhouse?

And they were insulators a thousand years ago.
So, how do they make the place warmer than it was a thousand years ago?

[Bored chemist]

A squashed fly on my windscreen slows the car down,

If the fly weighed a third as much as the car, it would probably be significant.

[Bored chemist]

Which is why I proposed a zero-cost,

Yeah; right...