The University Network

Scientists Reconstruct 150 Years Of Ocean Warming

A new method to reconstruct global ocean temperature changes since 1871 estimates that the ocean absorbed as much energy during 1921-1946 as it did during 1990-2015.

Noticeable changes in warming and sea level rise throughout the past 60 years have been caused, in part, by changes in ocean circulation.

This innovative mathematical approach, which was led by researchers from the University of Oxford, lets scientists track how ocean circulation has caused the changes in ocean temperatures over time.

“Our approach is akin to ‘painting’ different bits of the ocean surface with dyes of different colors and monitoring how they spread into the interior over time,” Samar Khatiwala, a professor of earth sciences at Oxford and co-author of the study, said in a statement.

“We can then apply that information to anything else — for example manmade carbon or heat anomalies — that is transported by ocean circulation,” he continued. “If we know what the sea surface temperature anomaly was in 1870 in the North Atlantic Ocean we can figure out how much it contributes to the warming in, say, the deep Indian Ocean in 2018.”

A full paper describing the method is published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

This development comes at a pivotal time.

As the oceans continue to suck up the world’s excess energy emissions, it has become increasingly important for scientists to understand how ocean circulation affects the trends and patterns of warming and sea level rise.

“The oceans absorb most of the excess energy in the climate system, leading to ocean warming. However, the patterns of ocean warming are not uniform,” said Laure Zanna, an associate professor in climate physics at Oxford and lead author of the study.

“This is due in part to the role of ocean circulation which redistributes heat,” she continued. “We wanted to understand the role of the ocean in setting observed patterns of ocean warming and associated sea level change.”

This method will be useful to explain increased warming in specific regions, Zanna explained.

There is still much work to be done to validate the method, but the researchers are confident in their approach.

“We were pleasantly surprised how well the approach works,” Zanna said in a statement. “It opens up an exciting new way to study ocean warming in addition to using direct measurements.”

But it is just a start. The researchers are working to refine their approach and improve their understanding of the drivers and the physics behind the changes in ocean circulation.

This knowledge is pivotal to help predict future patterns of ocean warming and sea level rise.