Glacial CO2

[Pmt111500]

This is an unanswered question in science, I think, since the Milankovitch cycles are thought likely to be the necessary primer for a glacial period to begin. However, the average value of CO₂ at the start of glaciation might have relevance in the interpretation of Holocene events (Early Anthropocene hypothesis). Thus the poll. There might be another threshold for getting an interglacial, comments on these, and other things on glacial cycles below. As hopefully is evident of the poll, this isn't intended as a very serious poll. Poll ends when the next glacial has begun, so no hurry to answer.

[modified poll because of Early Epica core records]

[Laurent]

Well, my guess is it is higher than 300 ppm because in the last million year there was 8 interglacial and 300 ppm was reached. I guess it is between 300 ppm and 350 ppm. Abruptslr did send a graph showing the first glacial era.
You should had some values above 290 ppm like 300 ppm, 310 ppm 320 ppm.
(I may not understand the question !?)

[crandles]

http://upload.wikimedia.org/wikipedia/en/6/63/Co2-temperature-plot.svg

Is it threshold to go below to get to a glacial period from a interglacial?

For a glib answer:
Given some temperature peaks appear to be before CO2 peak and imperfect correlation, I am inclined to say CO2 is not the only factors and so the answer is 'it depends'.

[Pmt111500]

 "I am inclined to say CO2 is not the only factors and so the answer is 'it depends'.", yes, and that's why this isn't too serious a poll. I should probably paraphrase the question as 'How low would the CO2 have to drop to start a Pleistocene sort of glaciation in Hudson Bay area or Scandinavia?', hmm, maybe I'll do that. There has been glacial periods in deep geologic time with higher CO2, I guess, but the intent was to find the other limit (350.org against global warming, and .... against a new glacial period ;-))

third way to ask: where would you put the lateral line between glacial and interglacial on the following (NGRIP) record and what is the corresponding C02

[ChrisReynolds]

I've voted 280 to 290, which is basically pre-industrial.

With the amount of CO2 we've put into the ocean/atmosphere system and the persistence of that (Archer/Brovkin), we will skip the next glacial at least. In "Storms of my Grandchildren" Hansen makes the point that even one factory producing CFCs could make sufficient forcing to offset the small Milankovitch forcing that initiates the slide into a glacial (then amplified by CO2 NO2 and ice sheet forcing), so as long as we retain the technology we can stop ice ages happening ever again.

Archer/Brovkin.
http://melts.uchicago.edu/~archer/reprints/archer.2008.tail_implications.pdf

The notion that global warming will last only a few centuries is widespread in the popular and even in the scientific literature on global warming. This misconception may have its roots in an oversimplification of the carbon cycle.

...Ultimate recovery (of the carbon cycle to pre-industrial CO2 levels) takes place on time scales of hundreds of thousands of years, a geologic longevity typically associated in public perceptions with nuclear waste.

[crandles]

Chris, why isn't that an argument for entering 229 or lower?

Is the question one that is at all relevant? Shouldn't we be asking what levels of CO2, in absence of geo-engineering, are consistent with Greenland not melting away (the not glaciating Canada and Scandinavia being an unimportant end of the range)?

(Or is greenland melting away something we can adapt to over the long timeframe that it will take?)

[ChrisReynolds]

It could well be Crandles, but it's Sunday and I can't bothered doing the maths. 

[Pmt111500]

Wili had found an answer here, so the poll is somewhat obsolete: http://forum.arctic-sea-ice.net/index.php/topic,728.0.html

So, it'd be 260.org against ice ages, then.

[Pmt111500]

Umm, not so fast.... discussion continues

On the Nature
link to Fig. 1.  Fig. 1g is for the North American ice sheet, Fig. 1h for the Eurasian ice sheet, and they both show the modelled ice-volume change with a constant CO2 concentration (blue, 160 ppm; black, 220 ppm; red, 260 ppm) expressed in Sea Level Equivalent relative to present.

So in their model constant 220ppm (e) is enough to drop the sea level almost as much as in true simulation with variable [co2] (100m vs.125m)! This is a great result since the low limit in the poll does not have to be changed. If reading the chart correctly, constant 260 ppm (sum of g & h) still produces almost 50m of sea level change. That's like half an Ice Age. Or, equivalent of tripling the Greenland Ice Sheet to Canada Arctic Archipelago and adding some serious amounts of mountain glaciers. Maybe their model does not answer the poll after all! Was Little Ice Age a prelude to glacial conditions (which humans interrupted) or not?

[JackTaylor]

Pmt111500: Reply #8;
"Was Little Ice Age a prelude to glacial conditions (which humans interrupted) or not?"

Or, we could ask, was the Medieval Maximum (medieval-warm-period) a prelude to current global warming but was interrupted by the Little Ice Age?

This has been discussed (and cussed) so much in so many places it's a matter of pick your choice.
Another kick to beat a dead horse probably won't hurt it, simply tenderize it.

My choice is volcano's interrupted the Medieval Maximum (medieval-warm-period) which was an early start to AGW caused by the increased burning of carbon products such as wood, peat, straw, coal, (heating-cooking, clearing land for farming, smelters,,, etc.....)

And, Little Ice Age (ca ~ 1350-1850) allowed the more severe effects of the Maunder Minimum (ca ~ 1645-1715) as compared to other solar minimums.

 Temps  http://en.wikipedia.org/wiki/Sp%C3%B6rer_Minimum

Volcano 1   http://www.sciencedaily.com/releases/2012/01/120130131509.htm

Volcano 2   http://www.archaeology.org/news/1348-131002-little-ice-age-lombok-volcano

I would like to hear your choice - answer for your question?
 

[Pmt111500]

I thought to get a sticker on the car rearwindow that says 'www.270.org', but it wouldn't get much exposure, since I don't drive much.