Kiwis solve global warming riddle

New Zealand scientists have helped solve one of the riddles of global warming by drilling deep into the ancient Antarctic rock.

An ingenious drill developed by Victoria University's Alex Pyne delved more than 2km through ice, sea and rock to pull out layers of ancient sea floor that were formed the last time greenhouse gases reached the levels they are now approaching.

The drill team, led by Victoria University Antarctic research centre director Tim Naish, found seas were warm enough to melt a large chunk of Antarctica's ice when atmospheric CO2 was only slightly higher than it is today.

The findings from the $30 million Antarctic Geological Drilling (Andrill) project were published in the journal Nature yesterday and may be used to help the Intergovernmental Panel on Climate Change (IPCC) update its predictions of sea level rise.

Mr Naish said scientists were given a "kick up the bum" in 2001 when the IPCC did not take into account melting West Antarctic and Greenland ice sheets because it did not think the science supporting it was strong enough. Scientists at a climate conference in Copenhagen last week decided there was now enough evidence to double the IPCC's predicted sea level rise this century from 0.5m to 1m.

The Andrill team bored a hole through a floating corner of the West Antarctic ice sheet about the size of Texas, called the Ross ice shelf, using drill parts adapted from Australian mining technology and sledged in by bulldozer.

The drilling found that when atmospheric CO2 reached 400 parts per million (ppm) - around 4 million years ago - it exaggerated a 40,000-year cycle of warming and cooling caused by tilts in the Earth's axis. That was enough to melt the Ross ice shelf and create the conditions to melt the entire West Antarctic ice sheet.

Mr Naish said New Zealand scientists drilled for 60 days before the ice sheet floated too far sideways and bent the pipe.

The Andrill team is still studying the cores to check just how warm the sea was when the ice sheet melted. Modelling suggests it could be about 5C.

When sea ice melted, remains of warm sea creatures floated to the sea floor. At other times ice stretched right to the bottom of the ocean, leaving glacial remains.

CO2 concentration in the atmosphere is now around 387 ppm, up from about 280 ppm at the start of the industrial revolution. Even optimistic IPCC predictions expect it to reach 400 ppm by the end of the century.

Publication of the research follows a climate congress in Copenhagen, Denmark, last week, where more than 2500 climate scientists and researchers told world leaders there was now "no excuse" for failing to act on global warming.

Victoria University climate scientist Andy Reisinger, who attended the summit, said some of the uncertainties in the predictions of the IPCC had been cleared up in the past year and new research showed sea levels would rise more in the next 20-30 years than had been expected.

The draft conclusions from the conference said a failure to agree strong carbon reduction targets at political negotiations could bring "abrupt or irreversible" shifts in climate that would be "very difficult for contemporary societies to cope with".