Atmosphere Ocean Science Colloquium

Tracking the thermodynamic and biogeochemical processes underlying climate change

Speaker: Prof. Jan Zika, University of New South Wales

Location: Warren Weaver Hall 1302

Date: Wednesday, November 29, 2023, 3:30 p.m.


When viewed using conventional Eulerian analysis tools, dynamic shifts in the climate system often dominate, while more gradual thermodynamic and biogeochemical effects are obscured. Those slower thermodynamic and biogeochemical processes are key to understanding climate change and climate model fidelity.

The idea of projecting climate data into coordinates which describe the underlying thermodynamic and biogeochemical state of the ocean (phase space) has been put forward. The oceanic version of this is known as the water-mass transformation (WMT) framework and has been useful in understanding the role of air-sea buoyancy fluxes and mixing in the time-mean ocean circulation. When such lenses are focused on the changing climate, they can filter out purely dynamic changes, but attribution of changes to specific thermodynamic processes is non-trivial. New approaches are needed which better clarify what changes in phase space mean in terms of the physical climate and new understanding is needed of how key physical and biochemical laws constrain changes in these spaces.

I will present recent progress by our team in improving phase space approaches. Our proposed approaches retain the benefits of classical WMT, but are (we think at least) easier to interpret and compare with Eulerian analysis. I will show how we have applied these methods to both observational and climate model data to attribute the thermodynamic and biogeochemical processes underlying climate change. Outcomes have included new understanding of where the ocean is taking up heat and quantification of changes in the atmospheric branch of the global water cycle.