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A common set of boundary conditions needed for the proposed experiments can be downloaded from here. The purpose of using common lower boundary conditions is to remove some sources of inter-model variance (e.g., sea-ice -albedo feedback) in order to better understand others. There will be no interannual variability in the boundary conditions to aid analysis of extreme events (better statistics).

The files are in netCDF format with values over land being 2.0E+20

SST and sea-ice concentration for control experiments

• Climatological monthly mean SST & sea-ice concentrations derived from the HadISST observations for 1961-1990. SST are in degrees C and sea ice coverage is either 1 or 0.
  • SST for control experiment (Figure 1: model climatological SST biases relative to the HadlSST)
  • sea-ice for control experiment

SST and sea-ice concentration for 2XCO2 experiments

• Monthly mean SST anomalies are added to climatological fields used for control experiments. SST anomalies are derived from 1% pa CO2 CMIP-type integration with HadCM3 model. The anomalies are the difference between two 30 year means: a) mean for period with CO2 values near present day b) mean for period with CO2 values near 2 x present day CO2.
  • SST for 2xCO2 experiment (Figure 2: model annual and mean SST anomalies)


• The monthly mean sea ice coverage is simply taken from the 30 year mean period with CO2 values near 2 x present day CO2 of the HadCM3 1% CO2 integration. In addition, the gridpoints are taken as sea ice covered where SSTs are less than -1.8C when the model SST anomalies are added to the control SSTs. This is due to the cooling over the North Atlantic associated with the weakening of the THC when CO2 increases in the model.
• sea-ice for 2xCO2 experiment.

Greenhouse gases

The Greenhouse gas concentrations for the control experiments are the mean concentrations for the period of 1961-1990. Only CO2 concentration changes for the 2XCO2 experiments. The concentrations for the control and 2XCO2 experiments are listed in Table 1 and Table 2. Table 1 is for models that require equivalent forcings. Table 2 breaks the Equivalent CFC-11 from Table 1 into specific concentrations and is for models that require specific concentrations.

Table 1: Greenhouse gases concentrations

Table 2: Decomposition of equivalent CFC-11 from Table 1

Land sea mask

• Land-sea mask