Understanding the impact of climate change on ocean eddy activity

Ever wondered how human-induced climate change can influence km-scale whirls in the ocean, so-called ocean eddies? The study by Beech et al. (2022) about long-term evolution of ocean eddy activity in a warming world, delves into this question by investigating the response of ocean eddy activity to anthropogenic climate change through climate modeling. Here is a summary of the key messages.

Specifically, the research employs climate change projections to analyze the variability and long-term trends of ocean currents and eddy kinetic energy (EKE) in different regions. By examining the representation of EKE in a climate model and comparing it with observed EKE from satellite altimetry data, the study aims to improve our understanding of ocean eddies – the weather of the ocean – and how they change in a warming planet.

This research field is crucial in the context of climate change because eddies are known to subsequently impact ocean systems through ventilation, volume transport, carbon sequestration and heat, and nutrient transport.

About the model

The study uses the AWI-CM-1-1-MR climate model. This model is used as part of the CMIP6 (Coupled Model Intercomparison Project Phase 6) ensemble, and it has been developed to simulate the Earth’s climate system. This model is also used in nextGEMS and one of its unique features is its variable-resolution ocean grid, which allows for a more accurate representation of eddy activity in the world’s oceans by employing enhanced resolution in dynamically active regions. The ocean component also utilizes a highly scalable and dynamical core, in addition to an unstructured mesh. This enables it to overcome the computational challenges associated with simulating long time series at sufficient resolutions needed to represent eddies.

How does anthropogenic climate change affect ocean eddy activity?

The study projects several shifts on ocean eddy activity due to anthropogenic climate change impacts, resulting in implications for various oceanic processes and circulation patterns. For instance, EKE is expected to shift poleward in most eddy-rich regions, whereas it is expected to intensify in the Kuroshio Current, Brazil and Malvinas currents, and Antarctic Circumpolar Current. Conversely, the Gulf Stream is projected to experience a decrease in EKE, which is due to a decline of the Atlantic Meridional Overturning Circulation (AMOC). Overall, these projections of EKE in the world’s oceans show pronounced transitions on a global scale. Furthermore, these changes are linked to broader climate elements such as the decline of the AMOC; the intensification of Agulhas leakage, and the shifting Southern Hemisphere westerlies.

The study shows that it is difficult to conclude something so robust from relatively short satellite time series. Additionally, the authors highlight it will be important to revisit the results of the study with truly eddy-rich models, like the ones employed in nextGEMS.

References:

Beech, N., Rackow, T., Semmler, T., Danilov, S., Wang, Q., & Jung, T. (2022). Long-term evolution of ocean eddy activity in a warming world. Nature Climate Change, 12, 910-917. https://doi.org/10.1038/s41558-022-01478-3