http://www.realclimate.org/index.php/archives/2005/03/how-long-will-global-warming-last/suggests
When you release a slug of new CO2 into the atmosphere, dissolution in the ocean gets rid of about three quarters of it, more or less, depending on how much is released. The rest has to await neutralization by reaction with CaCO3 or igneous rocks on land and in the ocean [2-6]. These rock reactions also restore the pH of the ocean from the CO2 acid spike. My model indicates that about 7% of carbon released today will still be in the atmosphere in 100,000 years [7]
If we stop emitting after releasing enough to get the peak up to 560ppm and half of it having been absorbed by oceans then if I am doing calculations correctly rather than falling back to 280 it tends to fall towards 280+1/4*2*(560-280)=420ppm by 1000 years and then takes a further 99,000 years to fall to 320ppm.
At 1,000 years where the GW effect could remain at over 3C for global average temperature (perhaps more if ice sheets collapse?). Calculated from 420ppm being over half a doubling and Earth system sensitivity at 6C. Temperature at the poles rise twice as fast as average so there could be around 6 or 7C temperature increase at the poles even after 1000 years. This might be enough to prevent an ice age starting?
At 100,000 years though, the GW effect at poles looks more like a 1C increase and that seems much less likely to be enough to stop an ice age starting.
So if there is no intelligent life, the Milankovitch cycles with periods of 21K 41k and 100k years will eventually come around to causing an ice age again. If the next is due in 2000 years then it could well be prevented even if we stop all our emissions at the 560ppm level and the delay to the next ice age could be a considerable length of time (41,000 years?). However if intelligent life is around, we seem quite capable of producing sufficient strong GHGs to ward off an ice age.
These calculations seem a bit woolly to me. There seems some disagreement perhaps because of lack of agreement on how long the CO2 lasts. I suspect the correct expert on this are CO2 cycle scientists. Someone that has just looked up a CO2 e-folding time of maybe 100 years or so without further research is likely to be wrong on this. I doubt scientists debate this much.
I have no idea but suspect there is room for disagreement on whether next ice age is delayed until next 41k year cycle or whether in 10k years further into 41k cycle the conditions could still be sufficient to initiate an ice age. Of course there is also room for discussion of the scenario of whether we stop burning fossil fuels at 560ppm or some other level or reduce the level but continue to produce some emissions or ....
