PNNL

The Science   

The effect of ocean heat transport on climate in polar regions remains uncertain, though studies suggest it plays a prominent role in high-latitude warming. Researchers at the U.S. Department of Energy's Pacific Northwest National Laboratory led a study that illustrates the key roles played by the atmosphere and ocean in transporting heat from lower latitudes to the poles, leading to a polar amplification of climate change.

The Impact

This study provides insight into the relative importance of the atmosphere and ocean in high-latitude warming. Analysis of Earth system model experiments shows that large-scale ocean dynamics appears to be of secondary importance to the local polar atmosphere and oceanic mixed layer in causing polar amplification. However, energy transported by the ocean is a more effective driver of polar amplification than energy transported by the atmosphere, suggesting a fundamental asymmetry in how effective these energy transports are in warming the high latitudes.

Polar warming has a range of impacts, including polar ice cap loss, global sea level rise, midlatitude weather extremes, and reduced oceanic biological productivity.

Summary

Researchers used a coupled atmosphere-ocean model to isolate the relative importance of ocean and atmospheric heat transport in environmental changes at high latitudes. Based on their analysis, they proposed a mechanism in which ocean and atmospheric energy transport have opposing effects on rising temperatures at high latitudes. These energy transport changes compensate in both hemispheres—increased ocean heat transport into the high latitudes is accompanied by decreased atmospheric energy transport.

This partitioning of the energy transport change between the atmosphere and ocean influences polar-amplified warming: When more energy is transported poleward by the ocean and less by the atmosphere, there is greater polar amplification of climate change. These findings reveal how interactions between local radiative processes and large-scale dynamic air and ocean motions shape how polar climates respond to greenhouse gas changes.

Acknowledgments

Sponsors: H.A.S is grateful for funding from Pacific Northwest National Laboratory's Linus Pauling Distinguished Postdoctoral Fellowship. B.E.J.R. was supported by National Science Foundation grant AGS-1455071. P.J.R. was supported by the Regional and Global Climate Modeling program of the Office of Biological and Environmental Research in the U.S. Department of Energy's Office of Science as a contribution to the HiLAT project.

Reference: H.A. Singh, P.J. Rasch, B.E.J. Rose, "Increased Ocean Heat Convergence Into the High Latitudes With CO₂ Doubling Enhances Polar-Amplified Warming." Geophysical Research Letters 44, 10,583-10,591 (2017). [DOI: 10.1002/2017GL074561]