(CN) — A genetic analysis of the Antarctic octopus purports to show that the West Antarctic Ice Sheet collapsed roughly 120,000 years ago, during the last interglacial. Perhaps alarmingly, temperatures in the Antarctic Sea were less than 2 degrees warmer than preindustrial levels.
That's according to a new paper published Thursday in the journal Science by a team of mostly Australian scientists, which suggests that the even minimal temperature rises have drastic consequences on the ice sheet — and therefore global sea levels.
"The marine-based West Antarctic Ice Sheet (WAIS) is considered vulnerable to irreversible collapse under future climate trajectories, and its tipping point may lie within the mitigated warming scenarios of 1.5° to 2°C (2.7 to 3.6 degrees Fahrenheit) of the United Nations Paris Agreement," the scientists wrote in the paper. "Our results provide the first empirical evidence that the tipping point of WAIS loss could be reached even under stringent climate mitigation scenarios."
The team of Australian researchers, led by Sally Lau, a postdoctoral research fellow at James Cook University, looked at the genetic history of Pareledone turqueti, or Turquet’s octopus. Modern populations of the octopus, which live deep in the ocean near the sea floor, are found in the Weddell, Amundsen and Ross seas, separated by the West Antarctic Ice Sheet. Lau and her team sequenced the DNA of 96 octopi.
They found that although the octopi in the different seas were genetically distinct, there were signs of "historic gene flow." In other words, the populations had at one point mated with each other. Demographic modeling suggested the mixing occurred during the last interglacial, or Eemium period, between 130,000 and 115,000 years ago. The authors conclude the mixing could only have been possible if the ice sheet, which now separates the three groups of octopi, had melted away.
That the West Antarctic Ice Sheet had once melted into nothing was first theorized by glaciologist John Mercer more than 50 years ago.
The issue of Science includes a perspective by two American scientists, Andrea Dutton and Robert Deconto, who are somewhat critical of the paper's conclusions. They argue that whether or not history will repeat itself — whether modern global warming will lead to the same melting of the ice sheets in Antarctica — remains an open question.
"Answering this question requires resolving additional questions about the timing, nature, and conditions of past deterioration of the WAIS," they wrote. "If the trigger occurred just before the warm period, then perhaps the simplistic emphasis on how warm it got during the interglacial should not be a focus."
They add: "The challenge in identifying a precise tipping point — and all the conditions thereof — is that the tipping point will likely not be apparent until it has been passed. Policymakers will always have to make decisions in the face of uncertainty about the future, and this latest piece of evidence from octopus DNA stacks one more card on an already unstable house of cards."
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