Friday, September 21, 2007

There goes another one . . .


We have all been treated to endless reps of CO2 is a response to global warming and not a cause, and I know because that is what happened as the Earth came out of the ice age. This, in spite of the fact that we know increasing CO2 can be both a cause of warming as it is today, when the gas is released by burning long buried fossil fuels and a positive feedback as gas is released from warming oceans and from soils. The accepted current guess for the lag is 800 + 600 yrs from Monnin, E., et al. "Atmospheric CO2 concentrations over the last glacial termination, Science, 291, 112–114, 2001. Such measurements are made using ice cores and critically depend on coordinating the age of the ice and the age of the gas in the ice. They differ in position and must be put on the same scale

Now comes a new core, Epica, and a new bunch L. Loulergue, F. Parrenin, T. Blunier, J.-M. Barnola, R. Spahni, A. Schilt, G. Raisbeck, and J. Chappellaz in Climate of the Past, 3, 527–540, 2007 to write on New constraints on the gas age-ice age difference along the EPICA ice cores, 0–50 kyr.

Here we bring new constraints to test a firn densification model applied to the EPICA Dome C (EDC) site for the last 50 kyr, by linking the EDC ice core to the EPICA Dronning Maud Land (EDML) ice core, both in the ice phase (using volcanic horizons) and in the gas phase (using rapid methane variations). We also use the structured 10Be peak, occurring 41 kyr before present (BP) and due to the low geomagnetic field associated with the Laschamp event, to experimentally estimate the 1ag during this event. Our results seem to reveal an overestimate of the lag by the firn densification model during the last glacial period at EDC. Tests with different accumulation rates and temperature scenarios do not entirely resolve this discrepancy. Although the exact reasons for the lag overestimate at the two EPICA sites remain unknown at this stage, we conclude that current densification model simulations have deficits under glacial climatic conditions. Whatever the cause of the 1age overestimate, our finding suggests that the phase relationship between CO2 and EDC temperature previously inferred for the start of the last deglaciation (lag of CO2 by 800±600 yr) seems to be overestimated.
They are loath to speculate about where this will leave the lag, even when encouraged to do so by the referees (unheard of behavior), but it is clear that this question is being looked into intensively. If Eli HAD to guess, he would say that there should be a lag based on first principles, but would not be much surprised if it shrunk down from the previous 800 year estimate, substantially.

This paper appears to have evaded everyone's radar.

UPDATE: Fergus informs me that William and he discussed this on Stoat when it appeared, As importantly Steve Bloom points to another interesting paper that Hank Roberts finds scary
IIRC the 800 years had been thought to mesh nicely with the turnover of the oceans, but there's a fresh paper in JGR that claims more like century-scale turnover. If correct that would mesh well with the EPICA result, but unless I'm missing something it would have some rather more important implications for present calculations of ocean heat content, the time needed to reach global warming equilibrium and the time needed for CO2 saturation.
Eli has found an open access version of the paper Radiocarbon-based circulation age of the world oceans by Katsumi Matsumoto.

11 comments:

fergus said...

Not everyone, Uncle Eli: William & U discussed this when it first appeared in CPD some months ago...

:)P

Anonymous said...

But Rabett, your guess would have been that the 2006 Arctic ice minima would have later than 2005 and covered less area than 2005. You would have been wrong. Your guesses are worthless, great for your fellow faith warmers to comment, but still worthless.

JohnS

Steve Bloom said...

Hey, *I* saw it too, unwashed though I am.

IIRC the 800 years had been thought to mesh nicely with the turnover of the oceans, but there's a fresh paper in JGR that claims more like century-scale turnover. If correct that would mesh well with the EPICA result, but unless I'm missing something it would have some rather more important implications for present calculations of ocean heat content, the time needed to reach global warming equilibrium and the time needed for CO2 saturation. I've seen three or four other papers in the last year that found deep ocean warming in progress in specific locales, so maybe this new finding is for real.

JohnS, you appear to care not at all whether your comments have any basis in fact. Try spending some time reading papers.

Deech56 said...

Well, we know that the CA crowd was too busy with minutia. While perusing that site, it struck me that their problem is that they examine small detail in a vacuum. In one of my few posts there I asked whether they planned to examine the Schwartz paper; when John V asked the same question, Steve McI wrote, "I’ve only got a certain amount of time, I can’t do everything in the word. I also try to do things that other people aren’t doing and it looks like other people are writing on Schwartz. I’d like to get to it some time." Had enough time to write a post on Tamino's RC post about the paper, though.

Anyway, by focusing only on the details, they (unlike you) fail to consider the context. They appear to believe that the big issue is inaccuracy in the data; it's not - the big issue is that by any relevant indication anyone chooses to examine, the earth is getting warmer and things will change. Are all the data perfect? No, but then there aren't that many perfect data sets in science, but science seems to progress.

Anyway, thanks for allowing my rant and keep educating us on the science and the meaning of the research.

Anonymous said...

Deech56 and details.

deech writes [Mcintyre]Had enough time to write a post on Tamino's RC post about the paper, though.

small detail, check who wrote the post. UC wrote it.

Details.

Hank Roberts said...

Auditing for OCR/typos,

"1ag" and "1age" -> "lag"?
(the first 2 have numeral "one" for lower case "L")

loathe -> loath

-------
Fascinating post on ocean circulation; I've seen two or three papers reporting increasing abyssal temperatures, and knew these were many centuries sooner than expected, but hadn't seen any comment on them; most helpful.

(Terrifying, but helpful ...)

EliRabett said...

Actually Evil Hank, ADD/typos

Deech56 said...

Anonymous 7:08 AM: Duly noted; however, my point still stands. ADD.

Hank Roberts said...

A bit of an excerpt, just to make the point that people need to read the actual article (and I left out a big chunk of detail below).

_____________excerpt_______
"The large reduction in 14C age in Figure 4 compared to Figure 1 suggests that the deep ocean circulation is more accurately described as centennial [Broecker et al., 1991; Stuiver et al., 1983] rather than millennial. This does not entirely negate the notion of a millennial timescale because circulation ages of 1000 years are found in the North Pacific (Figure 4). However, basin-wide, average erroneous first impressions that one gets from conventional
ages (i.e., 1000 years in the Atlantic and 1000 years in the
Pacific).[25] The new circulation 14C ages summarized in Table 1
are broadly consistent with the centennial replacement times
of Stuiver et al. [1983]....

"The new map of 14C ages (Figure 4) accounts for important pitfalls when interpreting the conventional 14C ages (Figure 1) in terms of circulation. Those pitfalls are not always obvious to those outside the field of chemical oceanography. Now there is a map that actually shows what the special IPCC [2005] report on carbon sequestration says about the age of the North Pacific deep water. ..."
--------end excerpt--------

This did make look for a vaguely recalled Calvin & Hobbes cartoon: Dad checks under the bed and says, "Yep, the monster's there again, hmmm, and tonight it's drooling. Well, good night, sleep well."

Anonymous said...

To the people who have used the lag to argue against CO2-induced global warming, it makes no difference whether the lag is 800 years or 800 micro seconds -- as long as there is a lag.

Hank Roberts said...

The short time for ocean circulation fits rather frighteningly well with Ward's scenarios for rapid change to a toxic atmosphere -- trouble by mid-this-century -- based upon the paleo work on warming of the deep ocean, in previous great extinctions.

Think layers of black anoxic shale in the strata, above layers of limestone full of fossils, but overlain by layers with very few fossils -- those mark the great extinctions of multicellular life, and a great era of success for the bacteria that thrive on sulfur.

http://www.newscientist.com/channel/life/mg19726421.900-mass-extinctions-the-microbes-strike-back.html

http://64.233.179.104/scholar?q=cache:7LCFXfPAFT0J:www.geotimes.org/current/feature_Geocatastrophes.html+%22peter+ward%22+extinction+microbes+sulfur&num=100&hl=en&lr=&newwindow=1&strip=1