Support for the Radiation-Intercomparison Project as part of the Chemistry Climate Model Validation exercise (CCMVal)

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment


Uncertainties in radiation schemes are a large source of error in climate studies. The PI is leading an international effort to validate the radiative transfer models used in Chemistry Climate Models (CCMs). This project is part of the SPARC CCM Validation (CCMVal) exercise. SPARC/WCRP recognise that CCMs require extensive validation and are providing the framework but not the funding to carry out this project. Phase I of this project is nearing completion and this NERC Small Grant proposal is to support Phases II and III of the project. Phase I. For this the PI collected and/or created (by stripping radiation subroutines out of main programs) offline versions of five GCM and CCM radiative transfer codes. Single profile clear sky comparisons of radiative heating rates and forcings were made and these were compared to those calculated with a sophisticated radiation model). This approach required substantial coding and debugging to get all radiation schemes performing on a single computer platform. Phase II will widen the comparison to the international CCM community and involve many more radiation schemes (12+), compared to the 5 analysed in Phase I. Groups themselves will need to perform the requested offline calculations. Heating rates, radiative temperature changes and radiative relaxation times will be compared in offline radiative transfer schemes for multiple clear-sky atmospheric profiles, simulating different months and different times of day. To explain the differences found between schemes it is also important to document the various parameterisations and approximations used in each code. Therefore it is necessary for the PI to visit modelling groups for a few days, impress on them the need for action and then to enlist willing scientists to help produce and/or document an offline radiation code. Following on from this contact groups will be required to submit calculations in a timely fashion and help with interpretation of the results. A suite of requested documentation and calculations has already been designed. Discovering causes of radiation scheme error will be an iterative process with the modelling groups performing additional calculations when requested. An independent set of reference calculations are also being performed by Dr Robert Portmann (NOAA-Bolder). Phase III will involve the CCM groups themselves with our input, employing the results from Phase II to improve their radiative transfer schemes and look at how improved schemes affect CCM integrations.
Description Radiation schemes used in climate models are important for how they represent climate change. The project found that recent improvements show that they are genreally fit for purpose, but still have errors representing stratospheric water vapour change
Exploitation Route Gives confidence in climate change models Climate modelling centres
Sectors Environment

Description Yes the CCMVal work has contributed greatly to IPCC reports and the underpinning of climate models for the World Climate Research Program Climate Model intercomparison Projects. These underpin climate science policy
First Year Of Impact 2010
Sector Environment
Impact Types Policy & public services

Description IPCC report authorship and citations
Geographic Reach Multiple continents/international 
Policy Influence Type Citation in systematic reviews
Impact IPCC reports influence the UNFCCC climate negotiations and government policy on climate change worldwide