Scientists shed light on ice sheet formation
An international team of scientists has discovered that the Antarctic ice sheet was potentially formed by a decrease in the levels of carbon dioxide (CO2). Presented in the journal Science, the study's findings highlight how this greenhouse gas was involved in the one of our planet's most significant climate events, and how it is contributing to the current and future climate scenario. Scientists from Australia, China, Sweden, the United Kingdom and the United States evaluated molecules from ancient algae found in deep-sea core samples. They identified a threshold for low CO2 levels below which an ice sheet forms in the South Pole. However, why CO2 must rise before the ice sheet melts is not yet known. Approximately 40% of CO2 dropped before and during the quick formation of a mile-thick ice sheet over the Antarctic some 34 million years ago, according to Professor Matthew Huber from the Department of Earth and Atmospheric Sciences at Purdue University in the United States. 'The evidence falls in line with what we would expect if CO2 is the main dial that governs global climate; if we crank it up or down there are dramatic changes,' co-author Professor Huber says. 'We went from a warm world without ice to a cooler world with an ice sheet overnight, in geologic terms, because of fluctuations in CO2 levels.' The team points out how our planet was warm and wet before the cooling period emerged, at the end of the Eocene epoch. Mammals, amphibians and reptiles shared both the North and South Poles, which had subtropical climates. Then, over a 100 000-year period, temperatures dropped significantly, killing off various species, shrinking sea levels, and covering Antarctica with ice. Sea ice and polar ice sheets influence the modern climate, as well as the global circulation of warm and cold air masses, says Yale University researcher and lead author Mark Pagani. They also impact precipitation patterns and wind strengths, and regulate global and regional temperature variability. 'The onset of Antarctic ice is the mother of all climate "tipping points,"' he says. 'Recognising the primary role CO2 change played in altering global climate is a fundamentally important observation.' Professor Huber points out how the findings of this study provide key insight behind the sudden cooling event. According to the team, the atmospheric CO2 levels for cooling that kick-start ice sheet formation are at about 600 parts per million. It would have been too warm for the ice sheet to form before the levels fell this low. The current level of around 390 parts per million helps maintain an ice sheet, but CO2 levels and temperatures are rising. The scientists predict that the levels will reach between 550 and 1 000 parts per million by 2100. 'The system is not linear and there may be a different threshold for melting the ice sheet, but if we continue on our current path of warming we will eventually reach that tipping point,' Professor Huber explains. 'Of course after we cross that threshold, it will still take many thousands of years to melt an ice sheet.' Commenting on the use of models to estimate the climates of the future, Professor Huber says: 'The models got it just about right and provided results that matched the information obtained from the core samples. This was an important validation of the models. If they are able to produce results that match the past, then we can have more confidence in their ability to predict future scenarios.' Professor Huber plans to research the impact of an ice sheet on climate. 'It seems that the polar ice sheet shaped our modern climate, but we don't have much hard data on the specifics of how. It is important to know by how much it cools the planet and how much warmer the planet would get without an ice sheet,' he explains.For more information, please visit: Science:http://www.sciencemag.org/Purdue University:http://www.purdue.edu/
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Australia, China, Sweden, United Kingdom, United States