Climate prediction models are sound — the proof’s in the plankton

Continents reconfigure, oceans shift, and ice sheets thicken and thaw, but for the past 95 million years Earth’s engine for distributing ocean heat has remained remarkably consistent.

That’s one of the findings of a new study featuring academics from the School of Ocean and Earth Science at the University of Southampton. The study tracks the  evolution of Earth’s climate system by using a novel approach to calculate the temperature difference between oceans in higher and lower latitudes. In doing so, the research offers a new way to gauge the accuracy of climate models.

The study appears in the journal Proceedings of the National Academy of Sciences and features Dr Gordon Inglis, a Royal Society Dorothy Hodgkin Fellow and Proleptic Lecturer.

“There are so many interlocking parts to climate science. What we’re doing here is trying to improve the foundations by testing some of the underlying dynamics of climate models that are used to predict future climate,” said Daniel Gaskell, first author of the study and a doctoral student in the lab of Dr. Pincelli Hull, a Yale Assistant Professor of Earth & Planetary Sciences.

One way to understand the global climate system is to envision it as a giant heat engine. That 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 — the difference in sea-surface temperatures between low and high latitudes — is an important measure of how well Earth’s heat engine is working.

It’s also an important factor in gauging how well climate models work to reconstruct the climate of Earth’s past and predict the climate of the future.

Yet scientists say it has been difficult to nail down reliable surface temperature data to test models. There are relatively few geological or biochemical proxies for past temperatures, for one thing. For another, there can be large disagreements between those proxy temperature estimates and climate models.

But the authors 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 so much,” Gaskell said. “Their shells carry an imprint of the seawater conditions at the time they were formed.”

The researchers used a combination of fossils from a single-celled organism called foraminifera to create a continuous, 95-million-year record of latitudinal temperature gradients.

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

And how do the current climate models hold up against this new temperature record? Quite well, the researchers say.

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

Dr Gordon Inglis, a co-author at the University of Southampton added, “the development of long-term, high-resolution temperature records is also vital for understanding other aspects of the climate system, including rainfall patterns, vegetation distributions and variety of biogeochemical processes. Understanding how these feedbacks operate in the past is crucial because they may help to amplify or reduce global warming”.