Yet another study has connected the ancient history of Antarctic ice sheets to atmospheric carbon dioxide, a climate parameter that humans are have a direct effect on. The findings follow last month's research that revealed that approximately 14 to 23 millions years ago, a loss of huge volumes of ice in Antarctica took place when carbon dioxide levels in the atmosphere were around 500 parts per million.
The new research stretches back even further, approximately 34 million years ago, during an era when the ice sheet's growth is believed to have originated. The results show that in this period as well, decreased levels of atmospheric carbon dioxide was connected to glaciation and the growth of ice sheets.
"Before 33.6 million years ago, there was no ice, and CO2 was above 750, was above the threshold," said Simone Galeotti, lead author of the new study. However, this didn't last for long - a transitional period with lower carbon dioxide and a variable ice sheet surfaced, followed by a period when the carbon dioxide levels went below 600 parts per million and the Antarctic ice sheet experienced a large expansion.
"This is one of the biggest climate changes that the planet has seen in the last 50 million years, when Antarctica went from being forested and vegetated, to really... it became glaciated at this Eocene-Oligocene boundary," said Rob DeConto, co-author of the study.
The team based their findings on a core of deep-ocean almost one-kilometer in length and examined sediment taken from the western part of the Ross Sea. The distribution of rocks in the various layers of the core suggests that icebergs were breaking off of an ice sheet approximately 32.9 million years ago, after emerging from the hot Eocene period.
Both the new findings and last month's research point to a "danger" threshold for ice sheets and potentially indicate a rapid melting event that may take place in the near future.
"As we go forward to a warmer world, we're essentially running this in reverse," said Thomas Wagner, a cryosphere scientist who was not involved in any of the research. "This work shows us what the world looked like back then that we're now heading toward."
The findings were published in the March 10 issue of Science.
