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Antarctic ice sheet formation was triggered by decline in carbon dioxide

By Robbie Anderson

New research seems to conclude that the presence of ice sheets on the Antarctic ice was initiated by a huge decline in the amount of atmospheric carbon dioxide.

About 34 million years ago when the, the formation of ice sheets started, it was preceded by the fall in the level of carbon dioxide fell by 40 per cent, suggesting that such massive falls in the greenhouse gas result in global cooling, and likewise the rises result in global warming.

Previous studies had indicated that atmospheric carbon dioxide over the Southern Ocean was actually rising during the Eocene to Oligocene climate transition, when the ice first formed. But the team of researchers said that accounting for the Southern Ocean currents and temperatures of that period, which are much different from today, it becomes quite obvious that the big freeze in Antarctica came after a decline in the level of carbon dioxide.

NSW Climate Change Research Centre researcher Dr Willem Sijp, said, "Our research recognized that the flows of deep ocean currents at the end of the Eocene were dramatically different from those of today because of the altered position and shape of continental masses. Previous research relied on different temperature estimates and had also not taken these different currents into account. This decline was a critical condition for global cooling and the emergence of the Antarctic ice sheet. In short, the apparent increase of CO2 during Antarctic glaciation is refuted."

Ocean currents are a bigger factor in calculating atmospheric carbon dioxide, because estimates of atmospheric carbon dioxide are derived from measurements of molecules from algae that are deposited on the ocean floor.

Matthew Huber, a professor of earth and atmospheric sciences at Purdue, said, "The evidence falls in line with what we would expect if carbon dioxide is the main dial that governs global climate; if we crank it up or down there are dramatic changes. We went from a warm world without ice to a cooler world with an ice sheet overnight, in geologic terms, because of fluctuations in carbon dioxide levels."

The Earth was once warm and wet, for 100 million years before the cooling, which occurred at the end of the Eocene epoch. Either poles were then inhabited by mammals and even reptiles and amphibians, as they then had subtropical climates. But then over the next 100,000 years, as temperatures declined drastically, many species of animals became extinct, and the ice-covered Antarctica and sea levels fell.

Pagani said, "The onset of Antarctic ice is the mother of all climate 'tipping points.' Recognizing the primary role carbon dioxide change played in altering global climate is a fundamentally important observation."

The researchers found that the point of transition in atmospheric carbon dioxide levels for cooling that marks the formation of the ice sheet formation is about 600 parts per million. The current level on Earth is about 390 parts per million, and so while an ice sheet remains, but carbon dioxide levels and temperatures are surging.

Huber said, "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. Of course after we cross that threshold it will still take many thousands of years to melt an ice sheet."