Dating tree cores
Whilst the Antarctic is a continent, the only major area of land in the Arctic covered with snow is Greenland.There have been several ice cores drilled in Greenland but these core do not go as deep as those in the Antarctic.Figure 6 shows the temperature for both the EPICA and the Vostok sites, which indicated that the temperature records are in good agreement for most of the time.Before approximately 200,000 years ago there was some divergence in the estimate age but as can be seen in Figure 6 these differences are well within the range of likely errors.Figure 8 shows the levels of Oxygen-18 from the Nevado Huascaran glacier in the Peruvian Andes.Levels of Oxygen-18 are positively correlated with temperature but this is reported not to be as accurate as when deuterium is also used in the calculation.
Indeed, dating information is sometimes given for the “ice age” and “gas age”.
Despite all of these limitations, it is generally accepted that ice cores give a good representation of temperature over very long periods.
They are able to answer such questions as what drives the cycle of ice ages and warm periods and what is the role of CO2 in long-term climate change.
Although not clear from this chart there is general agreement that temperature changes precede CO2 changes during the rising phase and CO2 lags temperature by a larger amount during the falling phase.
Figure 4 and Figure 5 show similar relationships for the Vostok ice core (note: EPICA ad Vostok are both in the Antarctic).