Large parts of the East Antarctic Ice Sheet did not retreat significantly during a time when carbon dioxide concentrations were similar to today's levels.
Three major ice sheets are being closely watched by scientists as global temperatures increase, glaciers melt and sea levels rise. Of the three, the East Antarctic Ice Sheet is the largest potential contributor to sea-level rise. Efforts to predict the East Antarctic's role in future sea-level rise have been hindered by an absence of data about the ice sheet's response to warming periods in the past. The geological history of the massive ice sheet has been difficult to pinpoint. Using ultra-sensitive analytical measurements that have helped to reveal the history of other ice sheets, a team of scientists has found that the East Antarctic Ice Sheet did not retreat significantly over land during the warm Pliocene epoch, approximately 5.3 to 2.6 million years ago, when atmospheric carbon dioxide concentrations were similar to today's levels.
Estimates of sea-level rise during the Pliocene have varied, from 20 feet to more than 130 feet higher than today. The upper end of this range would imply that much of the ice on the planet melted, which all together holds enough water to raise sea levels by over 200 feet. If the land-based East Antarctic Ice Sheet was stable during the Pliocene, however, as Jeremy Shakun, an assistant professor of Earth and Environmental Science at Boston College, and colleagues suggest, the Pliocene total could have been at most about 100 feet. According to Shakun and his scientific team, "Atmospheric warming during the past eight million years was insufficient to cause widespread and/or long-lasting meltback of the East Antarctic Ice Sheet margin onto land."
The findings suggest that some ice on the southern continent could be stable in a warming climate, but do not signal that Antarctica can somehow backstop the impact of climate change, the researchers caution. Ongoing emissions mean that atmospheric carbon dioxide levels will soon surpass the benchmark set during the Pliocene, the last time Earth experienced carbon dioxide levels higher than 400 parts per million. "Based on this evidence from the Pliocene, today's current carbon dioxide levels are not enough to destabilize the land-based ice on the Antarctic continent," stated Shakun. "This does not mean that at current atmospheric carbon dioxide levels Antarctica won't contribute to sea level rise. Marine-based ice is already starting to add to sea level rise and alone could contribute as much as 20 meters. We're saying that the terrestrial segment of the ice sheet is more resilient at current carbon-dioxide levels".