Our Ancient Ocean Temperature Records May Be Wrong Meaning Current Warming Is Unparalleled for 100 Million Years

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Scientists retrieving samples from the Arctic Ocean in July, 2011. NASA/Reuters

Scientists may have miscalculated ancient ocean temperature records. If confirmed, the discovery throws decades of climate research into question and could mean we are living through a period of climate change unparalleled for at least 100 million years.

It is generally accepted among the scientific community that ocean temperatures were around 15 degrees Celsius warmer 100 million years ago than they are today, during the Cretaceous period.

The Cretaceous period saw the highest global temperatures for the last 200 million years, because of the way the continents were positioned, with ocean circulation preventing the formation of ice sheets.

Scientists estimate ancient ocean temperatures using cores of sediment removed from the ocean floor. These contain the fossils of tiny marine organisms that lived at the time. By analyzing their calcareous shells, researchers can look at the content of oxygen-18—a natural, stable isotope of oxygen that provides information on the temperature at the time.

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The Indian Ocean seen from space. NASA

For the last 50 years, scientists have based estimates on paleoclimates using this technique. One of these calculations showed ocean temperatures 100 million years ago were far warmer than they are today and this estimate has been used as a staple in climate change research for decades.

However, in a study published in Nature Communications, a team of scientists from Europe has called into question the validity of oxygen-18 readings from this time. They looked at whether the fossils in the sediment cores had not remained constant over the millions of years they were trapped there.

To find out, the team exposed the organisms to high temperatures in artificial sea water containing oxygen-18. They then looked at how oxygen-18 was incorporated into their shells. Findings showed that the level of oxygen-18 can alter over time without leaving any trace of this change.

Representational image. Microfossils from marine sediments from the Antarctic continental margin. Hannes Grobe/CC

"What appeared to be perfectly preserved fossils are in fact not. This means that the paleotemperature estimates made up to now are incorrect," lead author Sylvain Bernard, from France's National Center for Scientific Research (CNRS)," said in a statement.

Instead of showing warm ocean temperatures 100 million years ago, the research indicates the changes seen are the result of the changing that take place during sedimentation, where the fossils reacclimatized to their new surroundings.

Further computer simulations in light of the latest findings indicate that in fact, oceans at this time were far cooler—and were fairly similar to temperatures seen today. If this is the case, the current period of warming is potentially far more concerning than previously realized.

Another study published in Science Advances in March 2017 indicated that the oceans are warming around 13 percent faster than previously thought. The European Environment Agency warns that global sea surface temperatures are around one degree Celsius higher now than they were 140 years ago and on the current trajectory, we can expect to see the first ice-free summers in the Arctic by the end of the century.

Anders Meibom, from the Swiss Federal Institute of Technology in Lausanne and an author on the latest Nature Communications study, said: "Oceans cover 70 percent of our planet. They play a key role in the earth's climate. Knowing the extent to which their temperatures have varied over geological time is crucial if we are to gain a fuller understanding of how they behave and to predict the consequences of current climate change more accurately."