@H2O MAN,
The main problem with the mathematical models of the IPCC is that they couldn't model cloud cover (of any kind) so they entered a dummy variable specified by their "scientists" to meet their a priori task of proving anthropogenic climate change due to CO2. After that was exposed and they became the laughingstock of the mathematics profession they promptly deleted their raw data, removing any doubts as to their competence.
http://climate.envsci.rutgers.edu/nuclear/
Volcanoes, nuclear explosions (groundbursts, but also airbursts, in brief everything except exoatmospheric), particulates from biomass burning, duststorms, etc, all result in increased cloud cover, however with chemically differential effects; this is a recent article with a good simulation model usable for volcanic eruptions as well. Btw, Tambora was vastly more powerful than the few Hiroshima-size explosions modeled here:
Quote:.....heating of the stratosphere by smoke..... strongly absorbs solar radiation. The smoke-laden air rises to the upper stratosphere, where removal mechanisms are slow, so that much of the stratosphere is ultimately heated by the localized smoke injections. Higher stratospheric temperatures accelerate catalytic reaction cycles, particularly those of odd-nitrogen...
http://www.pnas.org/gca?allch=&submit=Go&gca=pnas%3B105%2F14%2F5307