By Juliet Eilperin
Washington Post Staff Writer
Thursday, December 17, 2009; A08
COPENHAGEN -- A new paper published online Wednesday in the journal Nature suggests that the world may face a long-term sea-level rise of 20 to 30 feet, even under a modest global temperature rise.
The study -- by Princeton and Harvard researchers -- focuses on a period known as the last interglacial stage, which occurred about 125,000 years ago. At that time, temperatures at the two poles were likely warmer than today by five to nine degrees Fahrenheit, which is what scientists expect could happen again if the average global temperature warms four to six degrees above pre-industrial levels.
The scientists collected 50 indicators of geological sea level from that time, including beach sediment and coral samples, and developed a statistical approach so they could compare them to each other. After factoring in how both the sea surface and the earth's surface responds to pressure from ice sheets, they determined a global temperature rise of 3.6 Fahrenheit would likely commit the planet to a long-term sea-level rise of at least 21.6 feet and possibly more.
The findings are significant because the estimate is higher than previous projections, which put the sea-level increase at between 13 and 20 feet at 3.6 degrees Fahrenheit, or two degrees Celsius, which is the temperature rise threshold that policymakers are hoping not to cross if they can seal a climate deal in Copenhagen.
Princeton University geosciences and international affairs professor Michael Oppenheimer, who co-authored the paper and is in Copenhagen observing the U.N.-sponsored talks, said the findings are "something to worry about."
"Is this the end of the world? No," he said. "Does it mean there's a premium on reducing the level of greenhouse gases as fast as reasonably possible? Yes."
"Also," he added, "it puts an exclamation point on the two-degree target."