Ice sheets more sensitive to climate change than thought

23 FEBRUARY 2016
Antarctica’s ice sheets more sensitive to climate change than previously thought

A team of scientists from New Zealand, the United States, Italy, and Germany has determined that Antarctica’s large land-based ice sheets may be more vulnerable to increasing global temperatures than previously thought.

The research, led by Richard Levy of GNS Science, Edward Gasson of the University of Massachusetts, David Harwood of the University of Nebraska-Lincoln, and Fabio Florindo of the Istituto Nazionale di Geofisica e Vulcanologia, confirms that Antarctica’s marine-based ice sheets (those connected to the ocean) are vulnerable to climatic warming.

It also shows that land-based ice will melt if these warm temperatures are maintained into the future. This would have significant consequences for future sea level rise.

“This research gives us a look into Earth’s potential future if greenhouse gas levels continue to rise and temperatures continue to climb,” says Dr Levy.

“Basically, large parts of Antarctica, particularly around the coast, will become ice-free. Melting of Antarctica’s massive land-based ice sheets will likely take thousands of years, but observations certainly suggest ice sheet melt is well underway.”

“I would like to think that we can slow down this glacial retreat or even stop it. I certainly find it hard to imagine Antarctica without its majestic ice sheets.”

How the research was conducted Scientists examined a one-kilometre-long drill core that contained layers of rock and sediment deposited during an interval in Earth’s past when atmospheric carbon dioxide (CO2) concentrations reached 500 parts per million, levels similar to those projected for the next several decades.

This amount of atmospheric carbon dioxide last occurred over 15 million years ago during an episode of global warmth known as the Miocene Climatic Optimum, a period when global average temperatures were at times up to 3 to 4 °C
higher than today.

What the researchers found "We found plenty of evidence for relatively warm conditions in Antarctica. Shellfish that today are unable to live south of our sub-Antarctic Islands flourished along the shorelines at the foot of the Transantarctic Mountains.

“Trees, shrubs, and grasses that are similar to those that grow in New Zealand’s alpine tundra regions were able to thrive in Antarctica’s Dry Valley’s, an area that is presently devoid of higher plant life. We also found evidence that the glaciers retreated far from the coast.”

Importantly, these intervals of past warmth occurred when atmospheric CO2 concentrations were similar to levels projected to occur within the next several decades in all but the most aggressive greenhouse gas mitigation scenario.

“We were able to link the environmental data from Antarctica to information gathered from other locations around the world. Our analysis showed that the episodes of peak warmth and ice sheet melt occurred when CO2 was at about 500ppm, only slightly higher than today.”

The researchers also found that Antarctica’s ice sheets grew larger when climate cooled and CO2 dropped to pre-industrial levels.

“Clearly the ice sheets are highly sensitive to relatively small changes in CO2 and temperature,” says Dr Levy.

At the same time, Dr Levy’s colleagues at the University of Massachusetts used computer models to simulate Antarctic ice sheet response to climate change. Led by Dr Edward Gasson, the research examined how the ice sheet changed in response to different levels of atmospheric carbon dioxide and incoming energy from the sun.

When CO2 concentrations were held at 500 parts per million, regions of the ice sheet that sit in the ocean disappeared.

This result was similar to previous modelling studies. However, Dr Gasson’s new simulations showed that large portions of land-based ice also retreated a great distance inland contributing tens of meters to sea level rise during episodes of peak warmth in the Miocene.

“Fifteen million years ago West Antarctica had a lot more area sitting above sea level, so it held much more land-based ice than it does today. Therefore we would not expect the same amount of sea level rise from land-based
ice melt under similar temperature increase in the future. But the outcome certainly suggests that land-based ice in Antarctica is more susceptible to melt than we previously thought,” says Dr Levy.

Details of their studies will be published this week in the Proceedings of the National Academy of Sciences.

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