Climate models

The fundamentals of climate models are sound – the proof is in the plankton

Continents are reconfiguring, oceans are shifting, and ice caps are thickening and melting, but over the past 95 million years, Earth’s engine for distributing ocean heat has remained remarkably constant.

That’s one of the findings of a new Yale-led study that tracks the evolution of Earth’s climate system with a new approach to calculating the temperature difference between oceans at higher and lower latitudes. Using marine specimens from ancient fossil records, the research offers a new way to assess the accuracy of climate models.

The study appears in the journal Proceedings of the National Academy of Sciences.

There are so many interrelated elements in climate science. What we’re doing here is trying to improve the foundation by testing some of the underlying dynamics of the climate models that are used to predict future climate,” said Daniel Gaskell, a Yale doctoral student and first author of the study.

Gaskell works in the laboratory of Pincelli shellYale Assistant Professor of Earth and Planetary Sciences and co-author of the new study.

One way to understand the global climate system is to think of it as a giant heat engine. This engine attempts to redistribute the sun’s heat from lower latitudes near the equator to higher latitudes near the North and South poles. The latitudinal temperature gradient (LTG) – the difference in sea surface temperature between low and high latitudes – is an important measure of how well the Earth’s heat engine is working.

LTG is also an important factor in assessing how well climate models perform in reconstructing Earth’s past climate and predicting future climate.

Still, scientists say it has been difficult to find reliable surface temperature data to test the models. There are relatively few geological or biochemical proxies for past temperatures, for one thing. On the other hand, there can be large disagreements between these proxy temperature estimates and climate models.

But Gaskell, Hull and their colleagues say they may have found a better approach to determining temperature gradients – and the proof is in plankton.

The chemistry of plankton shells tells you a lot,” Gaskell said. “Their shells bear an imprint of the seawater conditions at the time of their formation.”

Foraminifera shells from a deep-sea sediment sample in the North Atlantic. (Daniel Gaskel)

Researchers used a combination of fossils of a single-celled organism called Foraminifera to create a 95 million year continuous record of LTG.

Our results show that the behavior of this temperature difference (LTG) has been remarkably consistent over time,” Hull said. “As the climate warms, the temperature gradient descends almost in a straight line, regardless of continental configuration or global ice volume.”

And how do commonly used climate models hold up against this new LTG record? Very good, say the researchers.

The models work better than we thought,” Gaskell said. “It means we understand this aspect of the climate system quite well and it implies that some of the more extreme scenarios are not as likely to occur.”

Other co-authors on the study were former Yale Institute for Biospheric Studies Donnelley Postdoctoral Fellow Charlotte O’Brien, who is now at University College London, Matthew Huber of Purdue University, Gordon Inglis from the University of Southampton and R. Paul Acosta and Christopher Poulsen from the University of Michigan.