CMIP forcing - ozone

Summary

Ozone is the third most important greenhouse gas after CO2 and methane. It is therefore crucial that climate models are able to account for changes in ozone concentrations in their both in the historical period, and their projections of future climate change.

This project aims to provide ozone forcing for the new phase of the Coupled Model Intercomparison Project, CMIP7, with a focus on exploitation of the available earth observation record.

Background

Anthropogenic activities since the industrial revolution, have substantially altered the chemical composition of the atmosphere including ozone concentrations, with far reaching consequences for the ozone layer, air quality, and climate. Resulting changes in stratospheric and tropospheric ozone contributed substantially to the overall climate forcing from anthropogenic greenhouse gas emissions since 1850.

The IPCC (2023) estimate ozone depleting substances to have caused a total negative radiative forcing of -0.15 (+/- 0.15) Wm-2, and tropospheric ozone precursors to have caused a total positive radiative forcing of 0.5 (+/-02) Wm-2 due to tropospheric ozone production. The tropospheric ozone changes thereby constitute the third most important radiative forcings since 1850 (acter CO2 and methane).

To be able to understand the climate impacts of ozone changes, climate models must be able to represent spatiotemporal variability in ozone concentrations, in the past and for future projections. However, the sources and sinks of ozone in the atmosphere are linked through complex chemistry to many other atmospheric species, which can render interactive-chemistry models too computationally expensive to be run for long-term climate simulations.

An alternative solution is to prescribe ozone changes in the radiation schemes of the Earth system models used, removing the need for interactive chemistry modules in the models themselves.

Aims and objectives

The overall aim of the project is to produce state-of-the-art ozone forcing fields for CMIP7. This will be achieved via the following primary tasks:

Moreover the overall aim is to work towards sustainable long-term production of future ozone databases in support of future CMIP phases, with a focus on maximising the exploitation of the available satellite (as well as ground-based) observational data records.

The project consists of the following tasks:

• Task 1: gathering of user requirements for the new generation of climate models
• Task 2: Extension of the existing CMIP6 ozone record to the present day
• Task 3: Update historical and future ozone forcing data in preparation for CMIP7
• Task 4: Develop a roadmap for the sustainable operationalisation of ozone forcing data.