A reader writes: where is the paleontological data showing the correspondence between CO2 levels and ice age events?. The answer is, all over the place; here is one possible source. The correspondence isvery good.
At this point, the s(k)eptics jump up and down and say, aha, but the T leads the CO2. To which the answer is, so what? The lead is small (on the scale of these things: maybe 800y) and hard to even measure (you certainly can't see it on the scale of that graph). We *know* it takes feedbacks between T and CO2 to create the ice age cycles, which because of their periodicity are presumed to have orbital forcing as their ultimate pacemaker.
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I recall reading somewhere (Petit maybe) that while temperature preceeds CO2 to a certain extent, CO2 rise preceeds de-glacation in the Northern Hemisphere. As you say, there are complicated feedback processes at work.
Chasing this down I found this:
http://www.globalwarmingart.com/wiki/Image:Phanerozoic_Carbon_Dioxide_p…
It shows, as a conclusion:
"Both measurements and models show considerable uncertainty and variation; however, all point to carbon dioxide levels in the past that have been significantly higher than they are at present."
But let's not forget about the trend being set in the past 200 years:
http://www.globalwarmingart.com/wiki/Image:Carbon_Emission_by_Region_png
And how does that relate to the past 400,000 years:
http://www.globalwarmingart.com/wiki/Image:Carbon_Dioxide_400kyr_Rev_png
So, even though there is a significant rise in CO2 since the last ice age, it still isn't as much as it has been in the past several million years. This doesn't mean that there won't be another ice age triggered by the current rise in CO2. It only means that the earth will recover from any catastrophe that is happening during this period of earth's life cycle. And that really could mean, since humans arrived since the last ice age, humans most likely will not survive the next ice age - which appears to be well on its way, say, in another 100 years maybe?
Would anyone care to comment on this?
[Why would there be "another ice age triggered by the current rise in CO2"? IT seems most implausible. You haven't been watching too many Hollywood movies have you? And why "appears to be well on its way, say, in another 100 years maybe?"??? -W]
It's also my understanding that when the CO2 drops the T follows the drop, so while increases might not be directly correlated due to feedback processes, decreases are always preceeded by drops in CO2. This suggests in previous non-human related climate change other events caused the rise in temperature, releasing CO2, and then temps were maintained until something trapped CO2 from the atmosphere. Now we're bypassing the first step, releasing tons of CO2, and it's warming things, as predicted by the relationship between high CO2 and higher global mean temp.
I guess what I'm saying is, CO2 hasn't preceeded global warming cycles before, but that's only because humans weren't there to dump tons of it into the environment. It always was a natural forcing agent and therefore secondary and a reinforcement to whatever primary process was increasing global temp.
So what? It means that the temperature was the primary driver - that was itself changing because of other reasons such as the solar output - while the concentration of gases such as CO2 or methane was a consequence.
http://motls.blogspot.com/2006/07/carbon-dioxide-and-temperatures-ice.h…
Saying that 800 years is too short that it can be neglected is childish. This lag can simply be measured, it is there, and our knowledge about it has clear implications even though (expletives deleted)
[Hi Lubos. Congratualtions on getting nearly to the end before veering off into rudeness. You must be getting old.
As to the correlations... the change from ice age to interglacial, or vice versa, takes many multiples of the lag time. What matters is the clear correlation between them. The fact that one starts off the feedback process is no great surprise. Given the orbital forcing, a lead from temperature is entirely unsurprising. But thank you for verifying my para 2 -W]
I thought Cuffey & Vimeux (2001) had resolved the greater part of the phase-lag question. (William -- please amplify. I'd really like to know more.)
Gildor & Ghil (2002), following the same path, show that the phase lag can be in either direction, depending on the season, and explain why very convincingly.
I am sure this will satisfy Lubos. snork! Almost got through that with a straight face.
Cuffey, K.M., and F. Vimeux (2001). Carbon dioxide and temperature covariation from the Vostok ice core after deuterium excess correction. Nature, 412, p. 523-527.
[Ummm... thats the first time I've read G+G: it didn't seem terribly convincing to me. I can't see the few kyr lag they claim is clear for november in their fig 1. And I don't see how it could possibly be clear: 2kyr is thinner than their thick line! I don't see anywhere where they demonstrate their assertion that phase relations can be different during different seasons. In fact the entire thing seems rather confused, or I am...
C+V seems rather more convincing, though... -W]
I had the impression that at least some important details were awaiting further ice core analysis; see the discussion at http://www.geol.ucsb.edu/faculty/lea/ . I'm very curious as to the relationship between this line of thinking and the two recent Milankovitch papers.
Steve, which research/discussion there, specifically?
You mean one or several of the papers under the 'Publications' link on that home page, I assume, but which?