Greenhouse gas experiment (GHG)
In GHG, the concentrations of the following greenhouse gases are prescribed as a function of time: CO2, CH4, N2O and several industrial gases, i.e., chlorofluorocarbons (CFC-11, 12, 113, 114, 115), hydrochlorofluorocarbons (HCFC-22, 123, 141b), hydrofluorocarbons (HFC-125, 134a, 152a), carbon tetrachloride (CCl4) and methylchloroform (CH3CCl3).
From 1860 to 1990, the annual concentrations of these gases are prescribed as observed and, from 1990 onward, according to the IPCC'92 scenario IS92a. For the industrial gases, the IS92a scenario has been updated to be consistent with a Copenhagen-like emission scenario (IPCC'96). All of the time dependent, or 'transient', forcing experiments have been initialized at year 100 of CTL, nominally 1860 in the transient experiments. However, these initial values do not correspond to 'pre-industrial' (1860) but to present-day conditions.
This applies not only to SST and other climate variables but also to the concentrations of CO2, CH4 and N2O. In the transient experiments, this initial shift in concentration is taken into account by enhancing the observed/projected concentrations of these gases in an appropriate way (Appendix A). Although this approach allows for a correct computation of the radiative forcing, it does not account for the warm bias in the initial climate state. This bias is maintained throughout the transient experiments so that a comparison with observations should be restricted to climate trends as a result of the imposed radiative forcings.
Corresponding Control Run is EH4OPYC_71413CTL and EH4OPYC_71413CTL_MM.