Does cloud cover effect or change the albedo of the planet?
No.
The emissivity of Earth is unknown. The presence of clouds do not affect it.
Albedo is the inverse of emissivity. Emissivity is also the same as absorbtivity. It is simply a measured constant of how well a surface emits or absorbs light as light is converted to thermal energy or as thermal energy is converted to light.
ALL frequencies of light are considered. There is no frequency term in the Stefan-Boltzmann law.
Only infrared light converts to thermal energy upon absorption. The absorption of visible light converts to chemical energy or ionization, not thermal energy at all.
Like the simple photosensor on an elevator door, or like in a plant, absorption of visible light does not convert to thermal energy.
It is not possible to measure the emissivity of Earth, because it is not possible to measure the temperature of the Earth.
It can
seem that clouds have a warming effect, because we tend to see them form when there is warm air at the surface (well, warmer than the upper atmosphere!), and moisture is available (water vapor, invisible). The cloud itself is not water vapor. It is liquid water or ice. They are formed by warm air containing moisture, cools as it rises. Cold air can hold less water vapor than warm air, so some is 'squeezed out' and becomes visible liquid water. This tends to happen at the same altitude, which is why clouds tend to be flat on the bottom. As the air continues to rise, it takes that liquid water with it, creating a 'piled up' look to the top of the cloud (cumulus cloud).
Lines of cumulus clouds indicate a cold front. Cold air is coming in and tossing warm air aloft. This is why after such a front passes, it feels cooler. This type of front can also produce the more violent storms. Such air is said to be 'unstable' by meteorologists. This means the air is cooling faster with altitude than the normal adiabatic rate. Warm air easily rises into this colder air, once given something to start it moving. Air flowing over a mountain range can get it moving this way, which is why storms and clouds tend to appear on the windward side of a mountain range and it tends to be clearer on the leeward side. Cold fronts tend to be fast moving, and often generate thunderstorms and/or heavy rain or hail.
Stratus clouds form a little differently. These types of clouds are common in the Pacific Northwest. Warm air arrives over colder air, carrying with it moisture from the nearby sea. As it descends into the colder air slowly, a 'sheet' is formed at the point where the air can no longer retain that much moisture. It isn't a fast moving event. This is essentially a warm front, where warm air comes in over the top of cold air and settles into it. The air is said to be 'stable'. This kind of front is often stationary, hanging around for days. In the Pacific Northwest, it is almost continuous during the winters around here. This type of front can create what is called freezing rain. It's rain, but it's so cold it turns to ice when it strikes the ground, covering everything in a thick sheet of ice and literally gluing cars to the ground. Portland, OR has a lot of this kind of weather, due to it's proximity to the sea and the Gorge to the east, where cold air is arriving from eastern Oregon.
On the 'dry' side (eastern Washington and Oregon), snow is less, but it tends to be fluffier, due to the colder temperatures there in the winter.
On the 'wet' side (western Washington and Oregon), snow is greater, but tends to be wet and heavy. Some locals refer to it as 'Cascade Concrete'. It takes a certain skill to ski well in it!
In other words, that 'warming effect' is the
cause of clouds, not the reverse.
