I picked up this tidbit on Judy Curry’s blog:
alistairmcd | November 13, 2010 at 11:43 am | Reply
When I posted on Real Climate pointing out the glaring error in the optical physics used in most if not all the climate models to predict cloud albedo from optical depth**, my post was taken down in less than a minute.
**Mie solved Maxwell’s equations for a plane wave so the assumption of constant ‘Mie asymmetry factor’ is correct only when light first enters a cloud. Also, substantial direct backscattering at the upper cloud boundary is ignored yet it has an opposite dependence on droplet size than diffuse scattering. Therefore, above a threshold ‘optical depth’, pollution causes a reduction of albedo, another form of AGW.
So, at the very least, the IPCC’s predictions of CO2-AGW should be reduced by a factor of about three, possibly much more if ‘cloud albedo effect’ heating explains most recent warming.
Was it the result of Asian industrialisation [the ‘Asian brown Cloud’]? As it’s self-limiting, this might explain why according to ocean heat content, global warming ceased in 2003 and will reverse once Asian aerosol pollution is reduced.
A bit more info on this from elsewhere on the net. The Author is Alistair Davidson. Hopefully he’ll call by and tell us a bit more about his discovery.
“the ‘two-stream’ approximations used to predict cloud albedo from optical depth and, in particular, the effect of aerosol pollution. There is no doubt whatsoever that they’re fundamentally wrong because light attenuation is from two processes, backscattering at the upper cloud surface shielding the cloud interior and backscattering due to internal diffuse scattering. Unfortunately, the approximations assume just the latter and that excess light from the upper surface of the cloud is steered out by predominately forward scattering.
However, that’s, a mistake apparently dating to Dutch physicist Van de Hulst, who made the assumption to fit experimental data from liquid sols. To do so, he assumed constant ‘Mie asymmetry factor’, using the value Mie got from solving Maxwell’s equations, and got a reasonable fit. However, he and apparently none of the successor physicists who used the idea, including Sagan, studied the fine print: Mie assumed a plane wave front boundary condition, only met as the wave enters the surface of the sol. In reality, for diffuse scattering, g is by definition operationally 0.5, giving symmetrical exit streams.
So, the fit of the equation is fortuitous and whilst it can be used to predict albedo from tau, use to predict change of albedo when pollution changes tau goes the wrong way.”
This also fits with the article on WUWT a couple of months back saying ‘black carbon’ or ‘soot’ to you and me, in the atmosphere causes warming.