1.  IGD is also known as “delta-age”.  It was back calculated from the ice age and gas age data, thus IGD.
2.  IGD is calculated from a physical diffusion model of the firn.
3.  IGD is related to local not global temperatures, although, of course these are linked.
4.  Atmospheric CO₂ is relatively uniform across the global. Although it is generally slightly higher in the northern hemisphere.
5.  Accumulation rates are not directly related to temperature.

Update:

It has come to my attention that a number of AGW supporters have attempted to attack my paper.  This is brilliant news because it demonstrates its significance and that it is perceived as a threat to their agenda.  The best part is that none of them have contacted me in order to ascertain the physical mechanism behind the correlation and thus they do not know the reason for the subsequent correction.  However, some have gone as far as making up a nonsense theory and use it as the basis for their attack. 

Check the paper for yourself and ask yourself why these individuals have behaved in this way.  I know the answer, do you?