Earth's wobbles affect climate say NZ scientists

"Wobbles" in the Earth's orbit are causing rapid changes to the East Antarctic ice sheet and leading to global climate changes and marked sea-level changes around the world, New Zealand scientists say.

Analysis of sediment cores from under the Western Ross Sea proved a scientific theory that cyclical variations in the Earth's orbit not only drove ice ages in the northern hemisphere, but also global warming and dramatic sea-level changes, they said.

The analysis also confirmed a link between expansion and contraction of the ice sheet and the Earth's orbital cycles, said Dr Tim Naish, of the Geological and Nuclear Sciences Institute.

Dr Naish returned to Antarctica last month to lead a team surveying sites for a new drilling programme along the side of the East Antarctic ice sheet and on the Ross Ice Shelf in the southern McMurdo Sound region.

He said in an article in Nature magazine that the analysis of cores from the three-year Cape Roberts Project, led by New Zealand, showed the East Antarctic ice sheet - larger, more stable, and theoretically less vulnerable to climate change - had been dramatically affected by long-term wobbles in the Earth's orbit.

The changes in the shape of the Earth's orbit, the tilt of the planet, and wobbling of its axis follow different cycles with durations of 20,000, 40,000 and 100,000 years. The extent to which these balance out each other is a key driver of ice ages and warm periods.

But Dr Naish and colleague Professor Peter Barrett, of Victoria University's Antarctic research centre, have shown the cores can provide useful indications of what humans can expect in climate change being brought about in a much shorter term by global warming.

Their findings have been hailed internationally as a major contribution to the understanding of the behaviour of the Antarctic ice sheets, based on the cores, dating back 34 million years, recovered in three seasons of drilling by the multinational Cape Roberts Project.

Research on the Cape Roberts core - the deepest taken from Antarctica - showed that nikau-like palm trees, beech forests, flies and beetles flourished in the Antarctic 33 million years ago.

The cores provide the most detailed record of ice fluctuations for the Antarctic margin from this period.

Scientists estimate that the fluctuations in the volume of the East Antarctic ice sheet could have driven global sea-level changes of up to 50 metres.

Dr Naish and another GNS scientist, Dr Stuart Henrys, and Professor Barrett, were recently awarded a three-year grant of $390,000 by New Zealand's Marsden Fund to undertake more research into ice advance-and-retreat cycles dated precisely in the Cape Roberts drill core.

- NZPA

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Intergovernmental Panel on Climate Change (IPCC)

United Nations Environment Program

World Meteorological Organisation

Framework Convention on Climate Change

Executive summary: Climate change impacts on NZ

IPCC Summary: Climate Change 2001