Antarctic drill core data set to galvanise sea level concerns

3news.co.nz, February 11, 2009

Important new findings on how the West Antarctic ice sheet melted the last time the Earth underwent global warming -- and the implications for rising sea levels in the current climate change -- are to be released next month.

The research is expected to show that for hundreds of thousands of years during the Pliocene era, between 1.65 and 5.2 million years ago, the West Antarctic was too warm to retain its ice cover, says Professor Tim Naish, director of Victoria University's Antarctic Research Centre.

He is co-science leader of the $30 million Andrill project on the ice, with Professor Ross Powell from Northern Illinois University in the United States.

"Antarctica's ice sheets have grown and collapsed at least 40 times over the past five million years," Prof Naish said.

"The story we are telling is around the history and behaviour of the ice sheet ... as an analogue for the future," he said.

Fifty top scientists meeting in Wellington are discussing new findings on the orbital controls for those changes, and the balance between atmospheric and ocean warming in influencing the changes.

A flood of scientific papers on the new drill core findings has already been sent to international journals such as Nature, Science, Geology and the Geological Society of America Bulletin by Antarctic scientists meeting at the Wellington-based research centre.

The scientists have been analysing samples and data from two drilling cores -- each over 1km long -- that New Zealand drillers collected in Antarctica in 2006 and 2007 during the multinational Andrill project.

The findings are expected to contribute to significant changes in the fifth assessment of the UN's Intergovernmental Panel of Climate Change (IPCC).

The IPPC has made projections of sea level rises ranging from 18 cm to 59 cm this century, but has noted that if the Greenland ice sheet melts proportionally to warming rates, then sea levels would rise by up to 79 cm this century, and eventually by 7 m.

Now the climate scientists will have hard data on how the West Antarctic ice has previously melted.

"The biggest finding from our project is that it was not possible to sustain a West Antarctic Ice Sheet for long periods," said Prof Naish.

"For up to 200,000 years it was too warm to have a significant ice sheet there -- yet atmospheric carbon dioxide was not significantly higher than where we are now, and where the IPCC say we definitely will be in the next 100 years."

Under the IPCC's most optimistic model, CO2 would reach 549 ppm by 2100, or roughly 50% more than today.

Though meltwater from the West Antarctic will eventually lift global sea levels by an average of 5 m -- the impacts will vary: levels may actually fall close to Antarctica but increase by 7 m in the northern hemisphere.

Prof Naish said some scientists developing computer models of ice-sheet behaviour argue that Greenland is already past the tipping point.

"We don't think that is the case yet with West Antarctica, though the Antarctic Peninsula is showing all the signs, with ice shelves collapsing," he said today.

But the jury is still out on whether a global effort to stabilise atmospheric carbon dioxide levels at 450-500 ppm might stave off loss of the ice sheet.

Recently-published satellite images indicate Greenland and West Antarctica are already jointly contributing an average of 1-2 m sea level rise each century -- rises which were not included in the IPCC prediction of a 59-cm rise in the next 100 years.

"They left that out, but it will be in the next IPCC report," said Prof Naish.

Computer models and the research underpinning them show that the bigger ice sheet in East Antarctica will likely remain relatively stable, though there is a debate around how stable that will be.

"It may be nibbled away at edges ... but a number of other lines of evidence make unlikely that we will lose half the East Antarctic ice sheet," said Prof Naish.

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