Ocean temperature change models may be flawed, study finds
A Swiss-French study points to inaccuracy in measures of oceantemperatures over thelast 100 million years, suggesting that the levelshave remained much more stable than previously thought. The evidenceraises “serious concerns” about current rates of climate change.
Global sea surface temperatures are approximately 1 degree higher now than they were 140 years ago. But on a much longer-term scale, ocean floor and surface temperatures, particularly in the polar ocean, were (until now) assumed to be 15 degrees warmer100 million years ago.
Now,a research team from various French and Swiss universities – including the Swiss Federal Institute of Technology in Lausanne (EPFL) and the University of Lausanne – havequestioned the methods used to make these historicalestimates. Their study suggests thattemperaturesat the ocean depths, and at the surface of the polar ocean, have been overestimated: rather than falling 15 degrees over the last 100 million years, these marine temperaturesmay actually have beenquite stable. The research has been published in the journal Nature Communications.
“If we are right, our study challenges decades of paleoclimate research,” said Anders Meibom of EPFL and the University of Lausanne.
The 15-degree figure was traditionally arrived at by measuring the prevalence of a certain oxygen isotope in the fossils ofmarine organismspulled from the ocean floor. The assumption was that levels of the isotope in the organisms varied according to the temperature of the water they lived in, meaning their fossils could give an idea of how warm the oceans were at the time.
Butafter subjecting these organisms to hot artificial sea water, the Swiss and French scientistsfound that the oxygen isotope levelcan in fact change without leaving any visible traces. This suggeststhat the fossils were not as perfectlypreserved as previously thought – and calls into question their reliability as ocean thermometers.
For Meibom, the importance of oceans – and ocean temperatures – for gauging shifts in temperature change over geological time is crucial, including for predicting the consequences of current climate change more accurately. By re-investigating the study of ocean temperatures with the knowledge gleaned from this experiment, the scientists are confident that they can more clearly understand the evolution over time.
swissinfo.ch and agencies/dos