The 'flickering switch' of late Pleistocene climate change

POLAR ice contains a unique record of past climate variations; previous Greenland ice cores have documented relatively warm 'interstadial' periods during the last glaciation and short (centuryscale) returns to colder conditions during the glacial to interglacial warming (see, for example, ref. 1). These climate features have also been observed to varying degrees in ocean sediment cores^2-4 and terrestrial pollen and insect records^5-7. Here we report electrical conductivity measurements from a new Greenland ice core, which confirm these previous observations, and also reveal a hitherto unrecognized mode of rapid climate variation. Fluctuations in ice conductivity on the scales of <5-20 years reflect rapid oscillations in the dust content of the atmosphere. This 'flickering' between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation.