[along with amplification of variability in solar radiation due to clouds/aerosols]
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 116, D18205, 13 PP., 2011
- RCM-simulated clear-sky dimming/brightening in line with observations
- All-sky signal dominated by cloud forcing in contrast to observations
- Temperature trends could not be improved with transient aerosol emissions
The present study applies a regional climate model with coupled aerosol microphysics and transport in order to simulate dimming and brightening in Europe from 1958 to 2001. Two simulations are performed, one with transient emissions and another with climatological mean emissions over the same period. Both simulations are driven at the lateral boundaries by the ERA-40 reanalysis and by large-scale aerosol concentrations stemming from a global simulation. We find distinct patterns of dimming and brightening in the aerosol optical depth and thus clear-sky downward surface shortwave radiation (SSR) in all analyzed subregions. The strongest brightening between 1973 and 1998 under clear-sky conditions is found in mid-Europe (+3.4 W m−2 per decade, in line with observations). However, the simulated all-sky SSR is dominated by the surface shortwave cloud radiative forcing (CRF). The correlation coefficient R between 5 year moving averages of the CRF and all-sky SSR equals 0.87 for all of Europe. Both model simulations show a similar evolution of cloud fraction and thus all-sky SSR due to the constrained circulation induced by the reanalysis at the lateral boundaries. For most subregions, the modeled differences in all-sky SSR due to transient versus climatological emissions are insignificant in comparison with estimates of the model's internal variability.
I must protest your use of a linear interpolation between 330 and 366 ppm CO2. Since the effect of CO2 on temperature is logarithmic (increasing CO2 in theory leads to a given constant 'forcing' per doubling). I calculate it (log(360/330)/log2)) as 14.94%, or, say 15%. 15% of 3.7W/m2 is 0.55W/m2 (rather than your 0.41W/m2) and gives a factor of 15 (rounded) rather than your 21.ReplyDelete
I realise this is slightly more favourable to the alarmists, butting getting it righ5t might deflect their criticism!