“Given the uncertainty in representing various cloud
processes in climate models…”
“MG08 includes the treatment of subgrid cloud variability
for cloud liquid water by assuming that the probability
density function (PDF) of in-cloud liquid water
follows a gamma distribution function.”
“subgrid variability of cloud liquid”
“The temperature of homogeneous freezing of rain was
changed from 40°C in the original MG08 scheme to 5°C
in the released version of CAM5 in order to improve the
Arctic surface flux and sea ice in the coupled climate
simulations [Gettelman et al., 2010]. We note that this
change has no physical basis,…”
“There are still large uncertainties in the mechanisms
of ice nucleation,…”
“..partially related to the subgrid-scale dynamics that are
not resolved in large-scale models..”
“The modeled cloud fraction, phase and spatial distribution
of cloud condensates have a significant impact on
modeled radiative fluxes…”
“In general, CAM5 underpredicts the
observed downwelling SW flux by up to 100 W m2…”
“Lognormal fitting parameters for the best estimate
aerosol particle size distribution are given in Table 1…”
“There is a threshold size separating cloud
ice from snow (Dcs), which is largely a tuning parameter…”
“CAM5 severely underestimates aerosol optical depth
(AOD) by a factor of 5–10…”
I mean, look. I dont know squat about cloud microphysics, and modelling them as outlined in this paper is truly fascinating and interesting work.
However, I know enough reading this paper to scoff at the statement:
“The science is settled….”
http://www.ecd.bnl.gov/pubs/BNL-96872-2012-JA.pdf