"The atmosphere is relatively transparent to visual radiation in sunlight, and it penetrates to the earth's surface where it heats up the land and the oceans and the lower reaches of the atmosphere in contact with the land and seas. These materials re-emit this radiation in the far infrared region of the spectrum into the atmosphere, which is highly opaque to infrared, mostly because water vapor is an extremely effective IR absorber, as you point out. It is difficult for this heat to radiate back into space; this is what causes the greenhouse effect and makes our planet warm and suitable for life."

Yes, but it's only warm a suitable for life at lower than 30,000'
in elevation.

This isn't much of a greenhouse affect above 30,000'. It's *cold* up there.

"However, at high altitudes, it is so cold that water cannot exist as a gas, it freezes into a solid, so the moisture does not play a role as a greenhouse gas where it matters, at the atmosphere/space interface."

The greenhouse affect, can be measured and experienced at lower elevation. It occurs less at higher elevation.

If only scientists would spend more time skiing.

If we were bird people and lived at high altitudes [30,000'] "where water cannot exist as a gas", our birdman scientists would not talk about a greenhouse affect.

But being monkey people who live in houses on the ground, we measure "earth's average temperature" by monitoring the air temperature in little white boxes 5' off the ground. We mark down the temperatures of the high and lows each day and we keep records of this.
Then a monkey notices that the oceans are much of the surface area of earth. And notices that the average ocean temperatures are fairly warm.

When you combine the land average temperatures and the ocean surface temperatures and we get a number of roughly 15 C as average surface temperature- btw, this temperature is dominated by ocean surface temperature.

[If we were dolphin people we might get the same average earth temperature- and not because dolphin people are particularly smart.]

So the monkeys say Earth's average temperature is about 15 C.
But then they determine the black body temperature of Earth is 255 K
http://en.wikipedia.org/wiki/Black_body
Or
"Black-body temperature (K) 254.3"
http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html

15 C in Kelvin is 273.15 + 15 = 288.15 K

So Black body temperature says Earth should be 254.3
and the monkey people thought it was 288.15 K

Why is Earth 33.85 C warmer than it should be?

Whereas the bird people are mostly interested in the sky, and in the sky the average temperature would be fairly close
to 254.3 K, so when they discover what Earth's black body temperature should be, they don't need an explanation for a large difference.