Human influence is a key agent of future ocean warming patterns

Scientists found that circulation changes on ocean warming patterns will decrease in influence, which may alter sea level rise predictions

The oceans play an vital role in regulating atmospheric processes and the climate, it also regulates changes in these processes by absorbing heat and carbon.

Researchers from the Department of Physics at Oxford University have found that the influence of circulation changes on shaping patterns of ocean warming will diminish in the future, despite having been identified and modelled as a key factor over the past 60 years.

Their findings, which were recently published in the journal Nature, are significant as regional sea level, which depends on patterns of ocean warming, affects coastal populations around the world. The better this situation is understood, the more chance that mitigation strategies can be put in place to protect these communities.

Results of this study show how these ocean warming patterns are likely to change.

The researchers suggest that compared to past data, there will be widespread ocean warming and sea level rise, including increased warming near the Eastern edges of ocean basins leading to more sea level rise along the Western coastlines of continents in the North Atlantic and Pacific Oceans.

Laure Zanna, visiting professor in climate physics at Oxford University said: “In the future, the imprint of rising atmospheric temperatures on ocean warming will likely dominate that of changes in ocean circulation.

“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 climate modelling to predict ocean warming

A new method developed by scientists at Oxford University uses climate models to suggest that ocean warming patterns will increasingly be influenced by the simple uptake of atmospheric warming, making them easier to predict.

This is in contrast to the past when circulation changes were key factors in shaping ocean warming patterns.

Changes in ocean warming due to the uptake of atmospheric warming is easier to model. Therefore, scientists hope that where previous models have struggled, this might become more accurate for future projections.

Lead author, Dr Ben Bronselaer, commented:

“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. 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.

Ocean warming and carbon uptake go ‘hand in hand’

The study shows that the global ocean heat and carbon uptake go hand-in-hand, and the uptake rates are set by the present state of the ocean. This relationship is what determined the method developed in this study.

As humans alter the stability of the ocean through global warming, the ability of the ocean to take up both heat and carbon is altered. A possible implication could be that reductions in atmospheric surface temperature are likely to be slower if emissions are not reduced fast enough. This is due to the coupling between heat and carbon uptake by the ocean.

While ocean carbon and heat are separate systems, this study shows that they are deeply interconnected, due the ability of the ocean to absorb these quantities. These results help explain why atmospheric warming depends linearly on cumulative carbon emissions.

Zanna added: “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.”

Building on this research, the scientists will now attempt to understand how the storage of heat and carbon in the ocean will affect the decline of atmospheric temperature and CO2 levels if carbon emissions start declining.

The full paper can be found here.