OK, so we’re back to the question of whether T leads CO2 in the ice cores, the skepics favourite talking point. The std.answer is “OK, so there is a lead (maybe) but…” (Stoat passim). The “but” is a good enough answer, and I suspect most people skip over the (maybe). But its important, because the lag/lead is not at all easy to establish, because the T comes from the ice (via d-o-18 proxy) and the CO2 comes from the bubbles. 800y+/-600 is the current “best guess”, but not certain.
Thanks to GH for pointing out Loulergue et al. [Meh, dead link. Try http://www.clim-past.net/3/527/2007/cp-3-527-2007.pdf perhaps] who propose that the T lead is much smaller or even that CO2 leads: Our results reveal an overestimate of the Δage 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. Our finding suggests that the phase relationship between CO2 and EDC temperature inferred at the start of the last deglaciation (lag of CO2 by 800±600 yr) is overestimated and that the CO2 increase could well have been in phase or slightly leading the temperature increase at EDC.
Now… I wouldn’t get carried away by this, since this isn’t definitive either – just interesting at this stage. And I have done no more than skim it. Its worth a skim, just to get some idea of how hard this relatively simple thing is to establish. Note that the paper is under review in an open-access journal, so jump in if you think you’re hard enough!