This dir contains the monthly time series for select surface variables (TREFHT, 
TS (=SST over ocean), PS, PSL, aice, surface fluxes), plus averaged 3-d fields for
U, V, T, Q, etc.) around 2xCO2, 4xCO2 and 8xCO2 from the 1%/yr CO2 increase runs. 
The *.anomaly.* files are deviations relative to the control climatology 
of years 1-80. 

The 1pctCO2 run (1%/yr CO2 increase with fully coupled sea ice), 
FixedIce run (1%/yr CO2 increase with fixed aice for flux calculations only, 
internal sea ice concentration (aice) varies with time) and PiControl run are 
those used in Dai et al. (2019, Nature Comm.) and Dai and Song (2020, NCC). 

Arctic sea ice loss is minimum before 4xCO2 in the FixedIce run and this small sea 
ice loss is not seen by the atmosphere or ocean. Arctic amplfication (AA) is very 
weak in the FixedIce run. 

Thus, the 1pctCO2 minus FixedIce difference represents the effect of AA, while FixIce 
represents the background warming effect without signficant AA, and the 1pctCO2 run
represents the combined effect from the background warming and AA (this is the case
for all CMIP model projections).