Bubbles in the ice

Temperature of the trapped atmosphere can be obtained by studying the ratio between the heavy isotopes of oxygen, such as 18O, and the more commonly found one 16O. The ratio 16O/18O is then compared to the composition of a standard sample of sea water, the so-called SMOW (Standard Mean Oceanic Water), and the difference is calculated (δ18O‰).
Ice formed in a cold period has a lower content of heavy isotopes, such as 18O, therefore δ18O‰ is negative compared to ice formed at higher temperatures. Specific tables allow us to calculate the average temperature of the air on the basis of the value of δ18O‰. This type of analysis, carried out on different cores in Antarctica and Greenland have permitted us to establish, for example, going back in time, the end of the last glaciation, around 13,000 years ago and its beginning, around 75,000 years ago; the interglacial period between the latter and older glacial episodes (120,000-140,000 years ago) had a warm climate and temperature was over 2°C higher than present, according to the reconstruction that was made using the Vostok core.
The analysis of the chemical composition of trapped air takes into account mainly the greenhouse gases, such as carbon dioxide and methane, considered the main cause of global warming. In fact, the analysis of the core shows that the content of these gases is naturally lower during the cold periods, corresponding to glacial periods, and increases when temperature increases. By studying numerous cores, it has been possible to reconstruct the trend in time of the two main greenhouse gases, and to identify different cold and hot periods.
The most significant result of this analysis is, however, the dramatic increase of these gases in the last 200 years – starting from the development of industrial activities – an increase that has no comparison with any other in the last 160,000 years. From the end of the last glacial episode to the beginning of the Holocene (a period of time of about 2-3,000 years), the carbon dioxide concentration in the atmosphere has increased by 70 ppm, and the same increase has been recorded from pre-industrial times until today (less than 200 years)! Data inferred from the study of glaciers thus allow us to reconstruct with great detail information on the climate and on the atmosphere of the past – essential in order to understand how the climatic system of our planet works and at the same time it rings a warning bell that should make us reflect and take necessary measures. Will we be able to make good use of the ‘advice’ our glaciers give us?

Special reports

From the Multimedia section