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On entering an era of global warming, the stability of the Greenland ice sheet (GIS) is an important concern (1), especially in the light of new evidence of rapidly changing flow and melt conditions at the GIS margins (2). Studying the response of the GIS to past climatic change may help to advance our understanding of GIS dynamics. The previous interpretation of evidence from stable isotopes ([δ.sup.18]O) in water from GIS ice cores was that Holocene climate variability on the GIS differed spatially (3) and that a consistent Holocene climate optimum--the unusually warm period from about 9,000 to 6,000 years ago found in many northern-latitude palaeoclimate records (4)--did not exist. Here we extract both the Greenland Holocene temperature history and the evolution of GIS surface elevation at four GIS locations. We achieve this by comparing [δ.sup.18]O from GIS ice cores (3,5) with [δ.sup.18]O from ice cores from small marginal icecaps. Contrary to the earlier interpretation of [δ.sup.18]O evidence from ice cores (3,6), our new temperature history reveals a pronounced Holocene climatic optimum in Greenland coinciding with maximum thinning near the GIS margins. Our [δ.sup.18]O -based results are corroborated by the air content of ice cores, a proxy for surface elevation (7). State-of-the-art ice sheet models are generally found to be underestimating the extent and changes in GIS elevation and area; our findings may help to improve the ability of models to reproduce the GIS response to Holocene climate., Ice cores from six locations (3,8) have now been synchronized to the Greenland Ice Core Chronology 2005 (GICC05) throughout the Holocene epoch (Fig. 1a). The GICC05 annual layer counting was [...]

An understanding of how climate events in the Northern and Southern hemispheres are related is one of the main issues of climate dynamics. A new study uses the atmospheric methane concentrations of air bubbles trapped in ice cores from Greenland and Antarctica to determine the timing of temperature change in the two regions. It is found that, on average, climate change in Greenland lagged that of the Antarctic by 1000-2500 years during the last interglacial period. Such a time delay suggests that the oceans play an important part in transmitting climate changes.

Air bubbles which were trapped in polar ice have been analysed and the concentrations of CO2 over various periods have been calculated. Changes in the climate over many thousands of years tend to change the concentrations of CO2 in the atmosphere. However, CO2 concentrations during rapid climate changes are less certain. Research into CO2 from Greenland and Antarctic ice has been inconclusive. An accurate time scale is required to compare the data from Greenland with the Antarctic and a method has been developed which uses concentrations of atmospheric methane from both the ice samples.

The acidity of glacial ice influences the direct current electrical conductivity across the ice which indicates that the ice was formed in cold, dusty periods, as ice having high alkaline dust content decrease the conductivity. The data from Greenland Ice-Sheet Project 2 (GISP2) and Greenland Ice-core Project (GRIP) ice cores are used in the study. The GISP2 and GRIP ice cores are drilled 28 kilometers apart from each other and electrical conductivity test is performed at various levels. The upper layers exhibit uniform electrical conductivity and a large discrepancy is found in the lower layers.

Analysis of an ice core from Greenland indicates that interglacial periods do not normally have as stable a climate as the current Holocene period displays. The stable-isotope record indicates that climate can change drastically within as little as a few decades. This implies that the current climate may not stay stable as pollutants and greenhouse gasses are added. The last interglacial may also have lasted longer than previously thought.

Oxygen isotope levels from an ice core taken from the summit of Greenland's ice sheet confirmed previous evidence for the episodic occurrence of interstadials or periods of comparatively warm climate during the last glaciation. These interstadials, which were from 500 to 2,000 years in duration, developed sporadically probably because of the highly complex and variable circulation of the North Atlantic.

Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5°C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time. [ABSTRACT FROM AUTHOR]