What does the chemistry-climate model UKCA have to say about methane and ozone

A grand challenge in the field of chemistry-climate modelling is understanding the connection between anthropogenic emissions, atmospheric composition and the radiative forcing of trace gases and aerosols.

My talk focuses on what a whole-atmosphere chemistry-climate model can tell us about methane and ozone. Methane is an important greenhouse gas but its treatment in chemistry-climate models can be improved by moving from the commonly used latitude-invariant ‘lower boundary condition’, which prescribes the methane concentration at the surface, to a flux-based emissions treatment. I’ll describe the impact of such an improvement on the performance of UKCA, a key component of the UK Earth System Model, UKESM-1.

Tropospheric ozone is a pollutant levels of which impact human health, agricultural productivity and radiative forcing. The second part of my talk will describe how a whole atmosphere chemistry-climate model allows us to attribute the drivers of the ozone budget. I’ll describe recent work examining how stratospheric ozone depletion has influenced tropospheric ozone and draw on a recent CMIP6 analysis of how tropospheric ozone will evolve over the 21st century.