Mark Webb

Areas of expertise

• Radiative forcing and feedback analysis.

• Evaluating cloud processes using satellite simulators.

• The tropospheric energy budget and the global hydrological cycle.

• The design of model intercomparison studies.

Current activities

Mark has been the lead co-ordinator of CFMIP since 2006, and has been involved with the project since its inception in 2003. He led the development of the CFMIP-2 strategy to improve the understanding and evaluation of cloud feedbacks in climate models and is currently working on co-ordinating project implementation.

International climate modelling groups are now running CFMIP-2 experiments as part of the latest phase of the Coupled Model Intercomparison Project (CFMIP5).  These contain additional diagnostics which support quantitative evaluation of model clouds using satellite data from active and passive satellite observations. They also contain high frequency diagnostics suitable for comparison with in-situ observations taken at various locations around the globe, and budget terms suitable for understanding the contributions of different physical processes to changes in temperature, humidity and cloud water/ice in the warmer climate. The CFMIP-2 experiments form a hierarchy linking climate projections from the fully coupled ocean-atmosphere experiments for the next IPCC assessment to fine scale reference models run at a single location, via relatively inexpensive atmosphere only experiments forced with realistic and idealised 'aquaplanet' sea surface temperatures.
 
Mark is also working on understanding the physical processes responsible for short and long timescale responses of clouds and precipitation to carbon dioxide and large scale temperature increases in climate models. This includes work with coupled ocean atmosphere models and single column models, the latter through the CGILS (CFMIP-GCSS Intercomparison of LES and Single column models) project.

Career background

• Mark has worked on understanding and evaluating simulations of clouds and water vapour in climate models since joining the Met Office in 1990.  

• Between 1990 and 1994 Mark worked on understanding clear-sky greenhouse effect and its dependence on water vapour, temperature and lapse rate, and developed a system to simulate clear-sky outgoing longwave radiation from ECMWF operational analyses.

• Between 1995 and 1997 Mark started to work on evaluation of clouds in climate models, and co-developed the International Satellite Cloud Climatology Project (ISCCP) simulator, a tool which allows quantitative evaluation of model clouds using satellite retrievals from ISCCP.  He applied this tool to assess the Hadley Centre, LMD and ECMWF models during the EUCLOUDS project, identifying compensating errors in cloud amount and optical depth.

• From 1998 to 2000 Mark applied the ISCCP simulator in the model development process, identifying the need for a cloud area scheme to address problems with coarse boundary layer resolution in Hadley Centre climate model at that time.  

• Mark spent 18 months, from 2000–2001, representing climate users in the commissioning of a new mass data storage system.

• 200–2005 — Mark co-ordinated and participated in the analysis of climate model cloud feedbacks in CFMIP-1, and his analysis of CFMIP and parameter-perturbed ensembles contributed to the Fourth IPCC Assessment Report conclusion that low clouds are the largest cause of uncertainty in climate sensitivity in the current generation of climate models.  

External recognition

Mark has chaired the CFMIP project since 2006.