A while back I noted a paper in CPD that questionned the "there is an 800 year lag of CO2 at deglaciations" meme which has become such a favourite of the septics recently (most people go with the "yes its true but irrelevant", but the maybe its not true is also possible). When I noted the paper before it was just submitted.
Now its had two reviews and an editor comment by the sagacious Eric Wolff, and to my eye it seems to have survived largely unscathed. Indeed the reviewers call for it to consider the consequences rather more, so there maybe interesting times ahead for the idea.
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Hopefully someone will try to use a few good (that is, can reproduce modern atmospheric CO2 trends based on known carbon emissions) carbon cycle models to model the CO2/T lag during the warming from the last glacial maximum, and compare the model-produced trends to both old and new interpretations of the ice cores.
Apparently some others still think the lag is real.
The paper I just linked identifies a lag during the last glacial as opposed to during deglaciations, but is there a reason to expect a lag during one and not the other?
[That paper identifies CO2 leading by several kyr during ceratin events. The situation, alas, seems to be unclear. People have decided that, since we have a CO2 lag, thats what we expect, so I don't know what will happen if it turns out there is no lag after all :-) -W]
As a mental exercise, let's flip it around, and consider the alternative: what if over multi-million historical timescales, CO2 always led dT? Would that actually make things easier for the AGW case?
Probably not. Because if CO2 was sponaneously increasing and decreasing before dT went up and down, we'd have to figure out who was emitting/absorbing the CO2. Do we know of any natural mechanisms that would change CO2 on such scales without first involving dT? I'm assuming no - or at least not that I know of.
If that is the case, the CO2 must *always* lag dT in the absence of an artificial/anthropogenic emitter. Therefore, it can't be used as an argument against AGW.
"If that is the case, the CO2 must *always* lag dT in the absence of an artificial/anthropogenic emitter."
I suppose the size of the lag (eg if it is so small as be able to be considered no lag, it could be on the century timescale) could have implications for the more immediate future?
> any natural mechanisms that would change CO2 on such scales?
What happens to propagation of tsunamis over the continental shelves once they are newly free of ice? Would that area have been kept exceptionally free of disturbance while the surface was frozen over, and perhaps be a bit more likely to become unstable once suddenly under open ocean and warming currents?
If so, perhaps methane hydrates:
"The permafrost reservoir has been estimated at about 400 GtC in the Arctic (MacDonald, 1990), but no estimates have been made of possible Antarctic reservoirs. The oceanic reservoir has been estimated to be about 10,000 to 11,000 GtC (e.g., MacDonald, 1990; Kvenvolden, 1998). This oceanic clathrate reservoir is thus enormous (at almost a third of the size of the deep ocean reservoir; Fig. 2), and only small changes in its extent can have major effects on the atmospheric reservoir. Even the permafrost reservoir is on the order of hundreds of gigatons, not much smaller than the total amount of carbon in the terrestrial biosphere."
http://ethomas.web.wesleyan.edu/ees123/clathrate.htm
"Around 8100 years ago, one of the largest landslides in the world occurred at Storegga, 100 kilometres north west of the Møre coast. An area the size of Iceland slid into the Norwegian Sea."
http://www.hydro.com/ormenlange/en/about_ormen/key_features/storegga_sl…
"In the early morning of 1888 March 13, roughly 5 km3 of Ritter Island Volcano fell violently into the sea northeast of New Guinea. ... These accounts represent the best available first-hand information on tsunami generated by a major volcano lateral collapse. In this article, we simulate the Ritter Island landslide .... The consensus between theory and observation for the Ritter Island waves increases our confidence in the existence of mega-tsunami produced by oceanic volcano collapses two to three orders of magnitude larger in scale."
http://www.ingentaconnect.com/content/bsc/gji/2003/00000154/00000003/ar…
Of if you don't like that one, reach farther, consider a possible sudden and massive spike in the quantity of carbonaceous dust pouring into the atmosphere from comets --- see the older Peiser/CCNet archives for much about that as a possible explanation for all sorts of things in the anthropological record.
Pie chart:
http://ethomas.web.wesleyan.edu/ees123/clathres.p.gif
A text post meant to accompany the pie chart above is probably still languishing in the spam filter; in brief:
Storegga slide; and as longterm sea ice melts off, isn't that going to allow more areas of continental shelf with hydrates to be exposed for the first time in tens of thousands of years to short term events like tsunamis? Look up "volcano collapse" and tsunami. I'd guess the ice shelf areas were able to be very stable through those events and now will be jerked around more with only open water above them.
http://www.agu.org/pubs/crossref/2007/2007GL029551.shtml
"... Atmospheric CO2 rose several thousand years before abrupt warming in Greenland associated with Dansgaard-Oeschger events, 8, 12, 14, 17, four large warm events that follow Heinrich events. ..."
[Indeed yes. Though I'm not sure what that is supposed to prove, and the spread is wide, and there are still gas/ice age problems.
BTW, apologies for your other comment sitting in the Q for ages -W]
Hank - thanks for the links. So if the CO2 record did in fact lead the dT, the ups and downs could be explained by the types of events that you refer to? Would we actually be able to figure out what was causing the CO2 going up and down independent of T?
I know, I know, it seems a silly exercise to try to figure out the cause of something that didn't happen. But I hope the point of the mental exercise is understandable.
Better look for an answer from a climatologist, I'm just another reader here. Short answer seems to be 'not known yet' for the events in the past. The current event, we know, is from fossil fuel use.
http://www.cosis.net/abstracts/EGU05/10296/EGU05-J-10296.pdf
Wikipedia:
http://en.wikipedia.org/wiki/Dansgaard-Oeschger_event
"Dansgaard-Oeschger events are rapid climate fluctuations during and at the end of the last ice age. ... about 11 500 years ago, averaged annual temperatures on the Greenland icepack warmed by around 8°C over 40 years, in three steps of five years ...."
"The processes behind the timing and amplitude of these events (as recorded in ice cores) are still unclear."
Our host will know if that's good info.
It's awfully fast, eh?
Those all were attempts to speculate on what kind of changes might cause an increase in CO2 without a previous solar/orbital warming.
Looking at that pie chart, if it's right, _half_ of the planet's easily available carbon is tied up in methane in shallow sediments on the continental shelves. To me that looks like a classic house of cards situation. The same way MSWord can build a document far larger than it can revise without eventually collapsing, looks to me like the planet can put far more carbon into clathrates than it can keep stable.
But I don't find any good info on existence, let alone dates of other such submarine slides, particularly say in the sediments under the sea ice around the Antarctic. I don't know if they are mapped and described well enough to say at all if they might correlate at all to the D-O events.
If I ever see farther than giants, it's only by getting in their hair.
D-O events were discussed well in a thread at RC. It's closed to comments. Good chart at the beginning.
http://www.realclimate.org/index.php/archives/2006/11/revealed-secrets-…
In today's news (original not yet found at NASA, link is to newspaper)
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/06/02/MNG4VQ6A0B1…
------excerpt------
David Perlman, Chronicle Science Editor---Saturday, June 2, 2007
NASA scientists reading signals from a satellite in orbit, and flying aboard a low-flying plane over Greenland, are finding fresh evidence of melting snows and thinning glaciers in vast areas of the massive island.
.... changes in the circulation of waters feeding into the Arctic Ocean are altering crucial patterns of ocean currents there with effects that are increasingly uncertain.
The pace of glaciers sliding into the sea along Greenland's southwestern coast "is speeding like gangbusters this year," said William Krabill, leader of a NASA team that has just ended a three-week airborne mission probing glacier dynamics with lasers and radar. ...
... seven years ago, ... glaciers were moving into the ocean at a rate of only about 6 feet a year.... flights this spring, covering 16,000 miles of Greenland's surface and coastal glaciers, revealed that ice along the southern coast is speeding to the sea at more than 75 feet a year ....
... Krabill's team has been monitoring the inland surface and the glaciers flowing into the sea every year for the past 15 years. ....
.... according to Marco Tedesco, ... at NASA's Goddard Space Flight Center .... last spring the snow on Greenland melted over an area of more than 375,000 square miles .... far more than the island's average summertime snowmelt area of 350,000 square miles ....
Eighteen years of the satellite observations .... last summer the island experienced more days of melting snow and at higher altitudes than the average of all the past years -- particularly in the southern part ....
Melting snow ... both Tedesco and Krabill said, for in many areas near the coast the water can drain through surface cracks and vertical passages inside the glaciers and reach bedrock where it lubricates the ice sheet and speeds the flow of the glaciers to the ocean.
-------- end excerpt --------
from: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/06/02/MNG4VQ6A0B1…