SEQUENTIAL RELATIONSHIP BETWEEN ATMOSPHERIC CO₂ CONCENTRATION AND SURFACE AIR TEMPERATURE ON ORBITAL AND MILLENNIAL SCALES

The sequential relationship between atmospheric CO₂ concentration (aCO₂) and surface air temperature (SAT) is one of the fundamental questions in the paleoclimatic studies of Quaternary. A good understanding of this relationship is relevant to understanding the issues of climate change that the human beings are facing at the present-day. The ice sheets in the Polar Regions have produced important data to the sequential relationship studies. However, ice sheet records are not without pitfalls. The earliest reconstructions of past climate and aCO₂ histories using ice core were carried out in Greenland, of which temporal ranges of the reconstructed results were generally short, with the longest record shorter than the last interglaciation. Moreover, carbonate dust and some other mineral particles included in the ice during the formation of the Greenlandic ice sheet, might have caused some chemical reactions with CO₂ as their by-product. These processes ultimately led to the CO₂ records reconstructed from the ice bubbles unfaithfully reflecting the aCO₂ back then. Although the existing chronological timescales of ice layers are of considerable high precision, the uncertainties in the chronological timescales of aCO₂ records are still biggish due to the lock-in depths of ice bubbles not being estimated accurately in some ice cores. This is a major obstacle in resolving the problem of SAT-aCO₂ sequential relationship. With the accumulation of more and more high-quality paleoclimatic records, there have been several high profile reports on the integration of multiple proxy records on larger spatial scales (no longer limited to Antarctic region) for SAT-aCO₂ sequential relationship analysis over the past few years. However, the results of these recent studies are data processing methodology dependent. The SAT-aCO₂ sequential relationship on orbital and millennial time scales remains an issue of debating.