Study finds ancient oceans were much colder than previously thought, implying global warming is unprecedented within the last 100 million years
By Andrew Griffin
26 October 2017
(The Independent) – Global warming might be far worse than we thought, according to a new study.The research challenges the ways that researchers have worked out sea temperatures until now, meaning that they may be increasing quicker than previously suggested.The methodology widely used to understand sea temperatures in the scientific community may be based on a mistake, the new study suggests, and so our understanding of climate change might be fundamentally flawed. [UPDATE: See this analysis of the story at Climate Feedback: The Independent makes a giant leap in stating that modern global warming could be “worse than thought” based on a single study.]The new research suggests that the oceans hundreds of millions of years ago were much cooler than we thought. If true, that means that the global warming we are currently undergoing is unparalleled within the last 100 million years, and far worse than we had previously calculated.Until now, scientists believed that the temperature of the ocean depths and the surface of the polar ocean 100 million years ago were about 15 degrees warmer than they are today. But they might in fact have stayed relatively stable – making the warming we’re currently undergoing far more alarming.”If we are right, our study challenges decades of paleoclimate research,” said Anders Meibom, the head of EPFL’s Laboratory for Biological Geochemistry and a professor at the University of Lausanne.”Oceans cover 70% 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.” [more]
ABSTRACT: Oxygen-isotope compositions of fossilised planktonic and benthic foraminifera tests are used as proxies for surface- and deep-ocean paleotemperatures, providing a continuous benthic record for the past 115 Ma. However, visually imperceptible processes can alter these proxies during sediment burial. Here, we investigate the diffusion-controlled re-equilibration process with experiments exposing foraminifera tests to elevated pressures and temperatures in isotopically heavy artificial seawater (H218O), followed by scanning electron microscopy and quantitative NanoSIMS imaging: oxygen-isotope compositions changed heterogeneously at submicrometer length scales without any observable modifications of the test ultrastructures. In parallel, numerical modelling of diffusion during burial shows that oxygen-isotope re-equilibration of fossil foraminifera tests can cause significant overestimations of ocean paleotemperatures on a time scale of 107 years under natural conditions. Our results suggest that the late Cretaceous and Paleogene deep-ocean and high-latitude surface-ocean temperatures were significantly lower than is generally accepted, thereby explaining the paradox of the low equator-to-pole surface-ocean thermal gradient inferred for these periods.
