An international research team led by the Spanish National Research Council (Spanish: Consejo Superior de Investigaciones Científicas, CSIC) and involving researchers from the University of Granada, has found a direct link between the changes in the earth’s orbit and the stability of the East Antarctic Ice Sheet.

Twenty nine scientists from twelve different countries participated in the study, published in the journal Nature Geoscience.

The results were obtained via the analysis of seabed sediments, transported by icebergs around 2.2 – 4.3 million years ago, and were collected during an expedition undertaken as part of the Integrated Ocean Drilling Program.

The data obtained reveals that climate change can have a significant impact on how polar ice sheets react to more minor energy changes caused by alterations in the earth’s orbit. As a result, sea levels can either decrease or increase by dozens of metres. The research shows that 2.5 million years ago, when the concentration of carbon dioxide in the earth's atmosphere was similar to current levels, the thawing of the East Antarctic Ice Sheet became widespread. “This study helps solve the mystery of how the Earth’s orbit around the Sun contributes to the stability of ice sheets”, states Carlota Escutia, a researcher at the UGR’s Andalusian Earth Sciences Institute, and who led the expedition.

“Greenhouse gas emissions have, nevertheless, a much greater energy impact than that exerted by changes in the earth’s orbit”, explains Escutia. Sediment analysis shows that the stability of the earth’s largest ice sheet is directly influenced by the stability of the sea ice in the oceans surrounding Antarctica. This sea ice, essentially a mass of frozen seawater, acts as a protective shield around the continent and the Antarctic ice sheets. This protective shield melts as a result of rising sea temperatures produced by greenhouse gas emissions. “The disappearance of this sea ice triggers the melting of the ice sheets, which consequently leads to rising sea levels”, observes Escutia.

Millions of years ago, when carbon dioxide levels were highly concentrated in the earth’s atmosphere, as is also the case now, and sea temperatures were slightly higher than at present, the oceans surrounding Antarctica could no longer sustain the sea ice. Escutia points out that “the disappearance of this protective shield allowed oceanic currents pushed by the winds to penetrate down to the base of the ice caps, causing them to melt”.

The study predicts a widespread melting of the East Antarctic Ice Sheet if we fail to reduce the carbon dioxide levels in the atmosphere.

Bibliography:

M. O. Patterson, R. McKay, T. Naish, C. Escutia, F. J. Jimenez-Espejo, M. E. Raymo, S. R. Meyers,, L. Tauxe, H. Brinkhuis, IODP Expedition 318 Scientists. Orbital forcing of the East Antarctic ice sheet during the Pliocene and Early Pleistocene Nature Geoscience. DOI: 10.1038/NGEO2273