Comments on ‘ Coupling of the hemispheres in observations and simulations of glacial climate change ’ by A . Schmittner ,

Fig. 1. Squared-cross-correlation as a function of lag between (a) the predictions of M1 and Antarctic temperatures, and (b) M2 predictions Schmittner et al. (2003) argue that during the last glacial period, at millennial timescales, temperature changes in Greenland preceded changes of the opposite sign in Antarctica by 400–500 yr. They provide support for this conclusion by comparing a simple conceptual model with synchronized proxies of polar temperature (Blunier and Brook, 2001). But further analysis of this conceptual model, using the same data, suggests the opposite—that Antarctica leads Greenland. A more conventional cross-spectral analysis of the raw observations also supports the conclusion that Antarctica leads Greenland, and indicates that this relationship applies to the band from 1/7 to 1/2 kyr . The conceptual model states that changes in Antarctic temperatures Ta are negatively proportional to Greenland temperatures Tg; qTa qt 1⁄4 sTg;