Phase relationships between Antarctic and Greenland climate records

Comparison of climate records from Antarctic and Greenland ice cores shows that the two regions respond asynchronously during millennial-scale climate changes. The apparent out-of-phase relationship between the records has been described as a climate "seesaw" in which cooling in the Northern Hemisphere is balanced by warming in the Southern Hemisphere. The same relationship has also been attributed to the initiation of climate-change events in the Southern Hemisphere, rather than the North Atlantic as is conventionally assumed. A simple statistical approach - band-pass filtering combined with lag-correlation tests-used to examine the phase relationships in more detail shows that neither an anti-phase nor a phase-lag relationship adequately describes the observations. Whereas Antarctic and Greenland climate records do exhibit approximate anti-phase behavior about 50% of the time, the), are generally in phase during cooling. A phase lead of Southern Hemisphere climate of 1000-1600 years is statistically indistinguishable from a lag of 400-800 years, whether for Dansgaard-Oeschger, Heinrich or longer-duration events. The "seesaw" or "Southern lead" appearance of the data arises from the fundamentally different characteristics of the climate time series, most importantly the absence of rapid warming events in Antarctica comparable to those in Greenland. To be consistent with the observations, climate models will need to capture these characteristics, in addition to reproducing the correct phase relationships.