General Circulation Models and RCPs

General Circulation Models (GCMs)

General Circulation Models (GCMs) are numerical models that represent physical processes in the atmosphere, ocean, cryosphere and land surface, are the most advanced tools currently available for simulating the response of the global climate system to increasing greenhouse gas concentrations.

Schematic illustration of GCM (courtesy of IPCC Distribution Data Center (DDC))

Numerous GCMs simulation runs have been implemented by various countries as part of the WCRP's Fifth Coupled Models Inter-comparison Project (CMIP5) in which the simulation outputs can be downloaded from its webportal. For SEACLID/CORDEX SEA, member countries within the Southeast Asia region use GCM model simulation ouputs archived at the Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy. In order for the GCMs to be integrated into the future, they require radiative forcing of future GHG emissions. These are provided by numerous hypothetical emission pathways and IPCC for the AR5 has chosen four of these pathways and referred them as Representative Concentration Pathway 8.5 (RCP8.5), RCP6.0, RCP4.8 and RCP2.6. Below is the schematic illustration of these RCPs. However, CORDEX employs only two RCPs i.e. RCP8.5 and RCP4.5. The SEACLID/CORDEX Southeast Asia follows this requirement and uses only RCP8.5 and RCP4.5.

Schematic illustration of IPCC RCPs (courtesy of IPCC Distribution Data Center (DDC))

Table below summarizes the GCMs to be downscaled and also the RCMs and RCPs to be used by SEACLID/CORDEX member countries: