Ancient Records Reveal Scary Sea-Level Scenarios

Sediment cores from below the Red Sea bolster two key tenets of climate experts, scientists reported Thursday: a three-foot sea level rise in a century is by no means extreme, and once ice sheets start to melt, that process is likely to accelerate for several centuries.

Using 500,000-year-old sediment cores, scientists from Australian National University reported that data covering more than 120 episodes of sea level change support those predictions of what Earth’s near future might hold.

“We can quantify how fast sea level rose in the past, in response to natural climate processes,” study co-author Katharine Grant, a climate researcher at the Australian National University, told NBCNews.com.

And that, the team said, offers parameters for what to expect in a world that most scientists believe is warming because of man-made emissions of greenhouse gases.

“Times with close to the modern amount of ice on Earth show sea-level rise rates of up to about 1 meter per century,” Grant said.  “This is in the range of sea-level rise predictions for the coming century, so what our study shows is that rise rates of this order of magnitude are not at all excessive or extreme but within the range of ‘normal’ climate variability for present-day-equivalent ice volumes.”

Co-author Eelco Rohling, also of the Australian National University and the University of Southampton, said the study is the first to show how long ice-sheet melting can persist.

"This happened within 400 years for 68 percent of all 120 cases considered, and within 1,100 years for 95 percent,” he said in a statement issued with the study.  “In other words, once triggered, ice-sheet reduction, and therefore sea-level rise, kept accelerating relentlessly over periods of many centuries."

What does that mean for Earth today?  "Man-made warming spans 150 years already and studies have documented clear increases in mass-loss from the Antarctic and Greenland ice sheets,” Rohling said.  “Once under way, this response may be irreversible for many centuries to come."

Ancient Records Reveal Scary Sea-Level Scenarios