by Julie Arblaster & Gab Abramowitz
The Coupled Model Intercomparison Project (CMIP6) Model Analysis Workshop was held in Barcelona from March 25-28, 2019, and provided the first opportunity for results from CMIP6 models to be discussed and presented by the modelling community. It was held in conjunction with the World Climate Research Programme’s (WCRP) Working Group on Coupled Modelling (WGCM) and organised by the WGCM’s CMIP panel. Members of each modelling centre and many of chairs of the 23 endorsed Model Intercomparison Projects (MIPs) were represented at the meeting. One day was held jointly with Primavera, a European Union project to develop a new generation of advanced and well-evaluated high resolution global climate models.
Dr Veronika Eyring, the chair of the CMIP panel started the meeting with an update on the status of CMIP6. A key discussion point for the meeting was the higher equilibrium climate sensitivity of many of the models compared to CMIP5 (see figure). The equilibrium climate sensitivity is defined as the equilibrium change in annual mean global surface temperature following a doubling of the atmospheric CO2 concentration and is diagnosed from the CMIP models from abrupt CO2 experiments using the approach of Gregory et al (2004). The ECS from the CMIP6 models at the time of the workshop ranged from ~2.6 – 5.7°C, compared to the CMIP5 range of 2.1-4.7°C (Flato et al., 2013). There appear to be two clusters, one centred around 2.5°C and another around 5 °C. The CMIP panel is currently preparing a perspective piece describing this outcome and a session at the American Geophysical Union’s Fall Meeting exploring the reasons behind the change is also planned. This issue is also discussed in a recent Science article, with developments in both forcing (e.g. aerosols) and feedbacks (e.g. clouds) potentially implicated in the increase in some models from their CMIP5 to CMIP6 versions.
Another interesting advance since CMIP5 is the development of key automated tools to evaluate and analyse the models. These community tools included ESMValTool and PMP and are currently being used by Intergovernmental Panel on Climate Change (IPCC) lead authors of the 6th Assessment Report (AR6) to update key figures and metrics when additional models are added to the CMIP6 archive. These tools allow for a more efficient and routine evaluation of the large CMIP6 dataset, complementing traditional research efforts.
- Flato, G., Marotzke, J., Abiodun, B., Braconnot, P., Chou, S. C., Collins,W., Cox, P., Driouech, F., Emori, S., Eyring, V., Forest, C., Gleckler, P., Guilyardi, E., Jakob, C., Kattsov, V., Reason, C., and Rummukainen, M.: Evaluation of Climate Models, in: Climate Change 2013: The Physical Science Basis, Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Stocker, T. F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S. K., Boschung, J., Nauels, A., Xia, Y., Bex, V. and Midgley, P. M., Cambridge University Press, Cambridge, UK and New York, NY, USA, 741–866, 2013.
- Gregory, J. M., et al., 2004: A new method for diagnosing radiative forcing and climate sensitivity. Geophys. Res. Lett., 31, L03205