In the discussion above there is reference to planets in space with no nearby stars and just the cosmic background radiation. The planet is either atmosphere-less, has a non-GHG atmosphere or has a GHG atmosphere. It also has either a water surface or a rock surface.
What about an atmosphere-less planet (called Vulcan) that is both solid (rock) and translucent at the surface with an optical depth of 50 metres. It is a grey body with an emissivity of say 0.85. What is the surface temperature? Is it higher than the cosmic background temperature?
The planet Vulcan is not transparent and it is not opaque. It is made of a substance intermediate between black obsidian and transparent silica glass.
Now put the planet into our solar system at the orbital position of the Earth. What is the new surface temperature of Vulcan? Presumably it is not the standard SB temperature of 255 k. It must be significantly higher.
If the surface temperature is substantially greater than 255 k then this must reduce the approximate warming that can be attributed to the greenhouse effect on Earth. This is because the Earth has an ocean that is an analogue for the translucent obsidian. The Earth’s translucent ocean lifts the average surface temperature regardless of the presence or absence of greenhouse gases in the atmosphere, so long as its surface does not freeze over.
An argument is made in a previous comment that with a non-GHG atmosphere the Earth’s oceans would evaporate, condense, and fall to the surface as ice, thereby freezing all water at the surface. This does not apply to Vulcan. Nor does it actually apply to the real Earth as the real Earth always has an atmosphere. In other words the argument is a red-herring.
So on Earth how much of the observed greenhouse effect is caused by the the translucent nature of about 70% of its surface, given that most of the ocean surface is not frozen, and how much is caused by GHG in the atmosphere?
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