A controversial study of ancient corals published this week suggests that sea levels can rise rapidly under global warming-type scenarios.

Paul Blanchon, of the Universidad Nacional Autonoma de Mexico, and his colleagues report in Nature that fossilized coral reefs uncovered during excavations for a Mexican theme park show that a sea-level leap of 2 to 3 metres occurred in the space of about 5 decades some 121,000 years ago. This was during the last interglacial period, when temperatures were higher than they are today.

“In our warming world, the implications of a rapid, metre-scale sea-level jump late during the last interglacial are clear for both future ice-sheet stability and reef development,” the researchers write.

“Given the dramatic disintegration of ice shelves and discovery of rapid ice loss from both the Antarctic and Greenland ice sheets, the potential for sustained rapid ice loss and catastrophic sea-level rise in the near future is confirmed by our discovery of sea-level instability at the close of the last interglacial. Furthermore, the inhibition of reef development that this instability caused has negative implications for the future viability of modern reefs, which are already being impacted by anthropogenic activity on a global scale.”

However a number of other researchers seem sceptical of the claims.

The key issue is how old the reefs actually are.

As the NY Times points out, the new study dated the fossil corals by analysing isotopes of thorium and comparing the Mexican reefs with other reefs in the Bahamas with accepted ages. The paper notes:

But in interviews and e-mail messages, several researchers who focus on coral and climate said that although such a rapid rise in seas in that era could not be ruled out, the paper did not prove its case.

Daniel R. Muhs, a United States Geological Survey scientist who studies coasts for clues to past sea level, cited a lack of precise dating of the two reef sections. William Thompson, a coral specialist at the Woods Hole Oceanographic Institution, agreed, saying that given the importance of the conclusion, Dr. Blanchon interpreted the physical features without enough corroborating evidence.

Scientific American points out that the researchers themselves admit some of their dating is “suspect” in their paper. National Geographic adds:

Tad Pfeffer, of the University of Colorado at Boulder, noted that Blanchon’s team couldn’t directly measure the rate of sea level change around the Mexican corals, because the age estimates aren’t accurate enough. Instead the study authors compared changes seen in Xcaret to those seen in reefs with well-established ages in the Bahamas.

“It’s an interesting idea, but one that for me is only suggestive and not compelling,” Pfeffer said. “I’d want to see something more solid than this if I’m going to buy the idea of such rapid sea level rise at the time [of the last interglacial].”