Greenland ice core hints at Earth's next big melt

An international team of scientists has drilled down through 2.5 kilometres of Greenland ice and uncovered a surprising picture of Earth's last big melt, a picture that suggests how today's ice caps will affect sea levels as polar regions get warmer this time around.

The new results were published online in the journal Nature this week in an article co-authored by an international collaboration of researchers known as NEEM (North Greenland Eemian Ice Drilling). The group includes scientist Jocelyne Bourgeois from Natural Resources Canada.

The NEEM researchers analyzed snow that fell during the last interglacial period, called the Eemian, around 130,000 to 115,000 years ago.

Researchers from Natural Resources Canada spent two seasons helping drill an ice core five times as deep as the CN Tower is high — the first core that has ever provided information about the entire Eemian period in Greenland.

The collaboration discovered that during the Eemian period, Greenland was about 8 C warmer than it has been for the past 1,000 years. That's about 6 degrees warmer than climate models had predicted, said lead author Dorthe Dahl-Jensen of the University of Copenhagen.

At the same time, the data also showed that only 25 per cent of the volume of the ice sheet melted, which suggests that the melt didn't contribute as much as expected to the rise in global sea levels, which was four to eight metres higher than they are today.

On one hand, that's good news, as Greenland has undergone alarmingly rapid warming in recent years. According to the NEEM scientists, Greenland's average temperature has been rising five times faster than the global average, but the new results suggest the impact on the oceans may not be as dramatic as others have predicted.

On the other hand, the results suggest that melting in Antarctica was likely the cause of the bulk of the sea level rise in the Eemian period, and that Antarctic melting could well give the oceans a boost during this current period of warming as well.

"That's bad news because, in Antarctica, several parts of the ice sheet are unstable," Dahl-Jensen said, implying that these massive sheets could break apart and change global sea levels quickly.

The NEEM findings also suggests that scientists need to keep a closer eye on melting in Antarctica.

Canadian scientists played a key role in developing the techniques to help tease information from the ice core, which was no easy feat, Dahl-Jensen said.

For example, she said, the Canadians took many surface core samples that helped scientists understand how the atmosphere imprints itself in the ice.

Based in part on the Canadian work, the scientists figured out that the proportions of different varieties of oxygen called isotopes are related to the surface temperature when the snow was falling. By analyzing the oxygen in the ice core, they were able to figure out the average temperature during the Eemian period.

To figure out how much the ice shelf melted, the researchers analysed the pressure of air trapped in bubbles in the ice. Air is thinner at higher elevations.

"By measuring the pressure of the bubbles, we can reconstruct the elevation," Dahl-Jensen explained.

According to Natural Resources Canada, its scientists did analysis of trends in climate and atmospheric contaminants and contributed to the first pollen record from a Greenland ice core.

Dahl-Jensen said analysis of the pollen and DNA from the ice core, which provide information about the plants that lived in Greenland during the Eemian, were a focus for the Canadians and isn't yet complete.

"Unfortunately, Canada has decided to tune down their activities of ice core research," she added. "To be honest, I don't know if they will ever achieve those goals, which is really sad."

Natural Resource Canada said its geosciences program is currently focused on understanding the geological response to a changing climate in priority areas for northern infrastructure development and the monitoring of "key glaciers" as indicators of climate change.

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