1) its possible to make something highly reflective, yet be completely black to the naked eye. Its possible that the spectrums that the clouds reflect are more along the lines of infrared, or other spectrums that the human eye does not see, and still be able to reflect more of the energy of the sun.

2) we are currently in, and have been for some time, a period where these clouds would not form as often or as much.

If the theory is correct, once the solar activity dies down, they will be visible more often and much more of them. this would cause a much higher rate of cooling, than current times. If we are indeed (and i see no reason to believe were not) in a period of global warming, then this could just as easy reverse that after the high levels of solar activity passes.

the more man learns, the more he realises, he really does not know anything.