July 27, 2011 | A new study that looks at rising sea levels during the warmth of the last interglacial period (130,000 to 120,000 years ago) finds that melting ice sheets contributed far more to rising sea levels than thermal expansion (the process by which oceans absorb heat and consequently expand). The study, which includes NCAR’s Bette Otto-Bliesner among its contributors, notes that ice sheets may be more sensitive to temperature than widely thought.

Sea level rise is one of the major threats posed by climate change. The different components that drive sea level rise—thermal expansion, melting glaciers, and the melting of the Greenland and Antarctic ice sheets—are not well understood.

For the study, the researchers compiled data from the last interglacial period, when sea levels were about 26 feet (8 meters) higher than today, and compared it to the results of computer simulations that calculated the contributions from thermal expansion.

They found that thermal expansion could have contributed no more than about 1.5 feet (40 centimeters) to rising sea levels during the period, with ocean temperatures at the time only about 1.3°F (0.7°C) higher than today. Melting from the Antarctic ice sheet, on the other hand, likely contributed from 13.5 to 19 feet (4.1 to 5.8 meters) to sea level rise, according to the study.

The results show that small amounts of warming may have committed the ice sheets to more melting than scientists have previously thought. They also help scientists identify the physical mechanisms that explain changes they observe in the paleoclimate record, which is important for making accurate future projections.

McKay, N., J. T. Overpeck, and B. Otto-Bliesner (2011), “The role of ocean thermal expansion in Last Interglacial sea level rise,” Geophysical Research Letters, doi: 10.1029/2011GL048280

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