Decreased carbon dioxide formed Antarctic ice sheet?

Turning a long-held climate shift theory on its head, researchers have found that decreased carbon dioxide (CO2) levels during a major climate shift 34 million years ago led to initiation of Antarctic glaciation.

The finding counters a 40-year-old theory suggesting massive rearrangements of the Earth's continents caused global cooling and the abrupt formation of the Antarctic ice sheet.

The long-held, prevailing theory known as "Southern Ocean gateway opening" is not the best explanation for the climate shift that occurred during the Eocene-Oligocene transition when the Earth's polar regions were ice-free, the study showed.

The textbook version has been that gateway opening, in which Australia pulled away from Antarctica, isolated the polar continent from warm tropical currents, and changed temperature gradients and circulation patterns in the ocean around Antarctica, which in turn began to generate the ice sheet, explained Matthew Huber from University of New Hampshire in the US.

"We have shown that, instead, CO2-driven cooling initiated the ice sheet and that this altered ocean circulation," Huber added.

For their study, researchers simply modeled the Eocene-Oligocene world as if it contained an Antarctic ice sheet of near-modern size and shape.

They explored the results within the same kind of coupled ocean-atmosphere model used to project future climate change and across a range of CO2 values that are likely to occur in the next 100 years (560 to 1200 parts per million).

The study, published in the journal Nature, will provide scientists insight into the climate change implications of current rising global CO2 levels.