New research has shown that ice sheets in Greenland and Antarctica are extremely sensitive to changes in ocean temperatures, raising concerns that sea levels may continue to rise for centuries. While it was previously known that sea levels rose several meters during the last interglacial period, between 129,000 and 116,000 years ago, but sea temperatures during this period were largely unknown until now. The research, published in the journal Science on January 20th, showed that sea surface temperatures in this period were similar to those of today.

Sea levels in the last interglacial period were six to nine meters above those of today.

The new research was based on data from marine sediment core records from 83 sites. Scientists compared the data from these sites to data from preindustrial times (1870 to 1889), and to data from 1995 to 2014.

University of Massachusets climate scientist Rob DeConto, said “This tells us that the big ice sheets are really sensitive to just a little bit of warming. That’s a really powerful message.”

During the last interglacial period (LIG), the climate warmed as a result of shifts in the Earth’s tilt, with resulting temperatures rising to 2 degrees celisus above those of today. The difference in climate was dramatic, with warmer climate species of animals found much further north, and forests as far north as above the Arctic Circle. The period is used as a reference for scientists examining how the ocean and atmosphere could change as a result of the current warming trend.

Sediment contains information about local surface temperatures as well as about global sea levels. Surface-feeding plankton show the water temperature, with the ration of calcium to magnesium in their shells dependent on water temperature. Scientists are able to determine the extent of continental ice shelves from another species of plankton, in which the ration of two different forms of oxygen varies based on the ratio of ice sheets to seawater at a specific time.

Researchers found that at the start of the LIG, sea surface temperatures were close to the pre-industrial average. 4,000 years later, temperatures had increased by 0.5 degrees Celsius, reaching a temperature close to the 1995-2014 average. This shows that the relationship between temperature and sea levels is direct, but that the process of change happens slowly. The full effects of warming on sea level may not be clear for hundreds or thousands of years.

University of Exeter climate scientist Professor Andrew Watson said:

“The good news is that with luck it will continue to rise slowly, so that we have time to adapt, but the bad news is that eventually all our present coastal city locations will be inundated.”

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