Future ocean warming depends on human decisions

A new study has revealed that human activities will be a major driver of ocean warming, which up until now has been primarily influenced by natural circulation patterns. In particular, the researchers identified an unexpectedly strong link between ocean heat and carbon storage.

The study findings are significant because regional sea level rise, which affects coastal communities worldwide, is strongly influenced by ocean warming.

The research shows that both ocean warming and sea level rise will become more intense, and some regions will be affected more than others. The study predicts that increased warming near the eastern edges of ocean basins will substantially boost sea levels along the western coastlines of continents in the North Atlantic and Pacific Oceans.

“In the future, the imprint of rising atmospheric temperatures on ocean warming will likely dominate that of changes in ocean circulation,” said study co-author Laure Zanna. “Initially, we might think that as the climate warms more, changes in ocean currents and their impact on ocean warming patterns will become larger. However, we show that that this is not the case in several regions of the ocean.”

Using a new approach to climate modeling, researchers at the University of Oxford found that ocean warming patterns will increasingly be influenced by the simple uptake of atmospheric warming. The modeling technique makes it easier to predict warming compared to earlier simulations that were based on changing ocean circulation patterns.

Since changes in ocean warming due to the uptake of atmospheric warming are easier to model, the researchers hope that their work will pave the way for more accurate projections.

Study lead author Dr. Ben Bronselaer began conducting the research while he was a PhD student at Oxford.

“I think it is an encouraging possibility that climate models, which struggle to simulate past ocean warming, might be better at predicting future warming patterns,” said Dr. Bronselaer. “Better prediction of warming patterns implies better prediction of regional sea level rise, which will help to mitigate climate impacts such as flooding on individual communities. Of course, we do need to understand predictions of ocean circulation better to solidify this result.”

“During our research, we found a surprising relationship between ocean heat and carbon storage which appears to be unique. While there is a connection between these two quantities that is not yet fully understood, we think we have made significant progress towards uncovering it.”

While ocean warming and carbon uptake are separate systems, the study shows that they are much more interconnected than previously realized. 

As humans activities pump more heat and carbon into the ocean, the state of the ocean is shifting. The research indicates that carbon emissions have a direct impact on atmospheric surface temperature.

“We find that the ocean’s capacity to absorb heat and carbon are coupled, and constrained by the ocean state,” said Professor Zanna. “This implies that the present ocean state will regulate surface warming whether CO2 emissions continue to rise or decline.”

“The rates of ocean warming over the past 60 years have been significantly altered by changes in ocean circulation, particularly in the North Atlantic and parts of the Pacific Ocean, where we can identify cooling over some decades.” 

“However, in the future changes in ocean currents appear to play a smaller role on patterns of ocean warming, and the oceans will transport the excess anthropogenic heat in the ocean in a rather passive manner in these regions.”

Based on their findings, the researchers will now investigate how the storage of heat and carbon in the ocean will affect atmospheric temperatures if carbon emissions are reduced.

The study is published in the journal Nature.

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By Chrissy Sexton, Earth.com Staff Writer