The temperature and salinity data were averaged over one degree squares at standard levels from 0 to 5550 meters. The duration of the averaging period was dictated by data availability considerations. At 250 and 500 meter depths, the eastern part of the subarctic gyre was also cooler and fresher for the later pentad, whereas the western part of the subarctic gyre was warmer and more saline. These changes are on the order of 0.5 C in temperature and .025-.10 parts per thousand in salinity and are consistent with an upward displacement of the potential density surfaces. Although no cycle of variability was observed from this study because only two time periods were examined, it is clear that large changes in the structure of the deep ocean occurred and that they were most likely due to changes in the dynamics and interactions of the climate system.
Natural variability is also apparent in the long-term paleoclimate record.
The observed climate changes are abrupt, with time scales perhaps as short as decades, and appear to have at least regional extent. Therefore, it seems that the relatively benign stable climate of the last 8,000 years is rather unique in the paleoclimate record. There are many papers in the literature dedicated to variability issues. The above are just examples. However, they suggest that even within the last century very important changes, oscillatory or long term, have occurred.