Jan Zika - Changes in ocean water masses reveal the distribution of excess heat in the climate system

Event type: 
13 May 2020
2.00pm - 3.00pm

Via Zoom - Zoom link TBA

Dr. Jan Zika
School of Mathematics and Statistics, UNSW Sydney
Climate Change Research Centre

Over 90% of the excess heat trapped in the earth system is contained in the ocean and the consequent thermal expansion was the largest contributor to sea level rise in recent decades. Since 2006 ocean warming and hence sea level rise has been spatially heterogenous, with some regions such as the Southern Ocean showing intense warming and others such as the sub-polar North Atlantic showing intense cooling. This heterogeneity may be due to spatial variability in the rate at which heat added to the ocean at the sea surface propagates into the ocean interior or to changes in circulation which redistribute the existing heat reservoirs within the ocean. However, the importance of these two mechanisms at a regional scale is unclear. Here we show that the spatial variability in warming and sea level rise is dominated by changes in ocean circulation. In some regions the redistribution term is 10 times larger than the excess heat component which is distributed much more homogenously across the oceans. In the North Atlantic, substantial excess heat uptake is balanced by cooling due to redistribution associated with a slowdown in the Atlantic Meridional Overturning Circulation.  Both circulation change and heat uptake drive intense warming in the Southern Ocean with an anomalous poleward heat transport of 118 ± 50 PW the largest effect. Our results suggest near term projections of sea level change will hinge on understanding and predicting changes in ocean circulation.

Biography: Jan Zika is a senior lecturer in the School of Mathematics and Statistics at the University of New South Wales, Sydney where he has been since 2016. He carries out fundamental research on the role of the ocean and water in the changing climate. He has led a team of researchers who used ocean observations to demonstrate that as the climate warms, wet parts of the globe are getting wetter and dry parts are getting dryer. His research has also helped to establish that the atmosphere is unlikely to become more energetic (windier overall) in a warming climate as having more water in the system makes the atmospheric heat engine less efficient. 

After completing a PhD at CSIRO in Hobart Jan has worked at the Université Joseph Fourier in Grenoble, the University of Southampton and Imperial College London and has been awarded both a National Environment Research Council Postdoctoral and Senior Fellowships. In 2018 Jan was awarded the Outstanding Early Career Researcher Award by the European Geosciences Union's Ocean Science Division and in 2020 he was awarded the Australian Academy of Science Anton Hales Medal.