Recent hemispheric asymmetry in global ocean warming induced by climate change and internal variability

Helen Elizabeth Phillips, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia, Saurabh Rathore, Institute for Marine and Antarctic Studies, University of Tasmania, Taroona, TAS, Australia, Nathaniel L. Bindoff, University of Tasmania, Institute for Marine and Antarctic Studies, Hobart, TAS, Australia and Ming Feng, CSIRO, Environment, Crawley, Western Australia, Australia
Abstract:
Recent research shows that 90% of the increase in global ocean heat content during 2005-2015 was confined to the southern hemisphere with no corresponding heat uptake in the northern hemisphere oceans. We show that this heating pattern of the ocean is driven by anthropogenic climate change and an asymmetric climate variation. This asymmetric variation in the coupled ocean-atmosphere system is identified in 11 climate models with 6000 years of simulations of pre-industrial variability. The observed hemispheric asymmetry is more pronounced in the 0-700 m ocean layer than in the 700-2000 m layer. While both layers experience steady anthropogenic warming, 0-700 m layer also has a stronger internal variability that we show is the primary driver of the observed hemispheric asymmetry. The rate of warming of our planet is tracking as projected from climate simulations. The changes in ocean heat content below 700 m have the strongest signal to noise ratio for tracking anthropogenic warming, however both layers indicate the robust detection of anthropogenic climate change without the need for other hypotheses, such as aerosols, to explain the asymmetry in ocean warming.
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