The Wikipedia entry for the Greenhouse Gas Effect states:
“If an ideal thermally conductive black-body was the same distance from the Sun as the Earth is, it would have a temperature of about 5.3 °C. However, since the Earth reflects about 30{154653b9ea5f83bbbf00f55de12e21cba2da5b4b158a426ee0e27ae0c1b44117} of the incoming sunlight, this idealized planet’s effective temperature (the temperature of a black-body that would emit the same amount of radiation) would be about −18 °C. The surface temperature of this hypothetical planet is 33 °C below Earth’s actual surface temperature of approximately 14 °C. The mechanism that produces this difference between the actual surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect.”
The statement is almost completely untrue. For instance not even the math adds up: the difference between the two temperatures +14 °C and -18 °C is not 33 °C but 32 °C. But it is not important, what is important here is the fact that there’s not a difference of 33 °C, nor of 32 °C between the hypothetical and real Earth surface temperature. In short, there is clearly a confusion about what is meant scientifically when describing the “surface” of Earth.
I don’t want to rewrite astronomic customs, but for such purposes as a black-body radiation flux equation to and from the planet using the Stefan-Boltzman law, we would think the surface of the Earth should be considered to be “the atmosphere”- not the surfaces of the sea and land. The reason being that it is only the uppermost layer of the planet’s mass that is capable of radiation – in the sense as defined by the Stefan-Boltzman equation – unlike the boundary of the vacuum of space beyond.
This confusion is a result of our human perspective. In the case of big gas planets like Jupiter we observe from the outside and hardly anybody would suggest the immediate exterior of its uncertain small diameter core was the “surface.”
Indeed, there’s an even stranger boundary custom to consider whereby we could discern the “surface” and atmosphere arbitrarily just at the point where Jupiter’s immense atmospheric pressures crosses 10 bar. Nonetheless, when talking about the Stefan-Boltzman law (i.e. about black-body radiation) as applied to Earth and it’s radiation budget, we should consider the gaseous atmosphere as being the Earth’s surface, not the actual surfaces of sea and land below.













