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CLIMATE/ Proof of global warming thousands of years ago

GIANLUCA LAPINI discusses the controversy over global warming, and the new discovery that could make help calm those who are worried about man’s contributions to the problem.

(Infophoto) (Infophoto)

The heated controversy, that has not died down, pitting those who argue that the ongoing climate change are man-made against those who attribute them to a natural variability in the climate of our planet, is the subject of interesting research conducted at the Department of Earth Science of the University of Syracuse (New York, USA). The results of this study, appearing in an article with a rather cryptic title (An Ikaite Record of Late Holocene Climate at the Antarctica Peninsula), recently published by the journal Earth and Planetary Science Letters, signed by Professor Zunli Lu and collaborators (with some previews appearing online in recent days), highlight the interesting role that "ikaite", a particular form of mineralization of the common calcium carbonate, may act as an indicator of climatic changes that occurred in the past.

For those unfamiliar with these issues, it is perhaps worth mentioning that scientists can only indirectly assess the ways in which the Earth's climate has evolved in the past, through the traces left by various natural phenomena sensitive to climatic conditions, collectively referred to as "climate proxies", for example, variations in the thickness of growth rings of trees, the contents of lake or ocean sediment, the pace of growth of stalactites in caves, the characteristics of the sediments of alpine or polar glaciers, etc.

The study mentioned above, then, demonstrates that the sediments containing "ikaite" may constitute a new type of climate proxy, based on the peculiar characteristic of the ikaite of incorporating some molecules of water into its crystal lattice. This mineral is in fact a hydrated form (to be precise, a hexa-hydrate) of calcium carbonate, which has the particularity of forming and remaining stable only at low temperatures. This odd property makes it particularly suitable to track the changes in average temperature which occur over time in the cold marine environments in which it forms. It is no coincidence that its name derives from the Ika Fjord, located in south-western Greenland, where it was first discovered and studied, in the years around 1963, by the Danish geologist H. Pauly.