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It is ridiculous to suggest N2 and O2 are not greenhouse gases just because the don't absorb IR


It is ridiculous to suggest N2 and O2 are not greenhouse gases just because the don't absorb IR24-02-2019 05:19
Tai Hai Chen
★★★★☆
(1013)
Earth reflects 70% of incoming shortwave radiation back into space. If it weren't for O2 and N2 absorbing that and reflecting that back to Earth as IR, Earth would be much colder than it is currently. So defining greenhouse gases as those that absorb in the IR is totally ridiculous IMO.
Edited on 24-02-2019 05:27
24-02-2019 19:17
Wake
★★★★★
(4021)
Tai Hai Chen wrote:
Earth reflects 70% of incoming shortwave radiation back into space. If it weren't for O2 and N2 absorbing that and reflecting that back to Earth as IR, Earth would be much colder than it is currently. So defining greenhouse gases as those that absorb in the IR is totally ridiculous IMO.


Firstly, O2 and N2 do not absorb much energy being emitted by the sun. O2 does have Rayleigh scattering which does reflect a percentage of blue light back into space, but this is not much. If you wear a blue shirt you can still see it is blue because most of the blue light band reaches the ground. O2 and N2 absorb in the UV but there is a rather sharp cut-off in these frequencies because the Sun is not a perfect black body and doesn't emit a lot of this. Though that which it does emit is very high energy. This is mostly lost in the Thermosphere and the Ozone layer. The lower frequency UV-A and UV-B so make it through and is why you wear sunscreen on summer days.

Approximately half of all of the heat from the Sun absorbed by the Earth is conducted into the Tropopause and then far more slowly into the Stratopause. At this point it becomes very complicated but we needn't address that here.

So while technically there is no such thing as a "greenhouse gas", what has become normal usage for that term should stress that CO2 is so slight a greenhouse gas that it cannot be counted as one at any levels above 200 ppm. THE "greenhouse gas" is H2O in its three phases that exist in the atmosphere. Nothing else in the quantities available is 100th the levels that H2O is. Any increases in CO2 above 200 ppm has no corresponding effect on temperature slowing of radiant energy.

What's more, there is so much humbuggery about the several gases that can absorb IR that the people making claims about these should be held up to public ridicule at every opportunity.
24-02-2019 21:46
Into the Night
★★★★★
(7664)
Tai Hai Chen wrote:
Earth reflects 70% of incoming shortwave radiation back into space.

1) The emissivity of Earth (the inverse of albedo) is unknown. No one knows how much light is reflected or how much is emitted by Earth itself. Emissivity is the same as absorbtivity. They are both the inverse of albedo, which is unknown.
Tai Hai Chen wrote:
If it weren't for O2 and N2 absorbing that and reflecting that back to Earth as IR,

Absorption and emission is not reflection. You cannot heat a warmer surface using a colder gas.
Tai Hai Chen wrote:
Earth would be much colder than it is currently. So defining greenhouse gases as those that absorb in the IR is totally ridiculous IMO.

It is totally ridiculous. No gas or vapor is capable of warming the Earth using any light coming from Earth's surface, whether it's emitted or reflected light.


The Parrot Killer
24-02-2019 22:09
Into the Night
★★★★★
(7664)
Wake wrote:
Tai Hai Chen wrote:
Earth reflects 70% of incoming shortwave radiation back into space. If it weren't for O2 and N2 absorbing that and reflecting that back to Earth as IR, Earth would be much colder than it is currently. So defining greenhouse gases as those that absorb in the IR is totally ridiculous IMO.


Firstly, O2 and N2 do not absorb much energy being emitted by the sun.

Both O2 and N2 absorb energy from the Sun, Wake.
Wake wrote:
O2 does have Rayleigh scattering

Rayleigh scattering is not absorption, Wake.
Wake wrote:
which does reflect a percentage of blue light back into space, but this is not much.

Rayleigh scattering does not reflect blue light back into space, Wake. It scatters blue light across the atmosphere, creating the blue sky we see instead of a black one during the day. We see the black one at night.
Wake wrote:
If you wear a blue shirt you can still see it is blue because most of the blue light band reaches the ground.

No, because you have sensors in your eyes specifically coded to detect this frequency, and your brain decides to call this signal 'blue'.
Wake wrote:
O2 and N2 absorb in the UV but there is a rather sharp cut-off in these frequencies

True, the absorption bands of both of these gases is quite narrow.
Wake wrote:
because the Sun is not a perfect black body

There is no ideal black body anywhere, Wake. It is a reference point, not any actual body. The Sun emits blackbody radiance. It is so hot it emits intensely at frequencies on up into the X-ray band, above the UV band.
Wake wrote:
and doesn't emit a lot of this.

It does, Wake.
Wake wrote:
Though that which it does emit is very high energy.

Energy is not solely determined by frequency, Wake.
Wake wrote:
This is mostly lost in the Thermosphere and the Ozone layer.

The frequencies above the UV-A band are heavily absorbed by the atmosphere, and especially by the oxygen in the atmosphere. Everything above UV-B never reaches the ground. A small amount of UV-B does, but it's intensity is quite reduced. More UV-A reaches the ground.
Wake wrote:
The lower frequency UV-A and UV-B so make it through and is why you wear sunscreen on summer days.

UV-A will tan you, but it will not burn you. Sunscreen is not necessary for UV-A. It is only used for the small amount of UV-B that does reach the ground. It's intensity is greatest from 10am to 2pm, local standard time. Sunburns appear an hour or two after exposure, which is why most people don't notice the burn until 2-4pm.
Wake wrote:
Approximately half of all of the heat from the Sun absorbed by the Earth is conducted into the Tropopause and then far more slowly into the Stratopause.

WRONG. Most of the energy absorbed from the Sun is radiated by the surface into space. See the Stefan-Boltzmann law. You keep denying this law.
Wake wrote:
At this point it becomes very complicated but we needn't address that here.

Nope. Complexity argument fallacy. See the Stefan-Boltzmann law.
Wake wrote:
So while technically there is no such thing as a "greenhouse gas",

There is utterly no such thing as a 'greenhouse' gas, Wake.
Wake wrote:
what has become normal usage for that term should stress that CO2 is so slight a greenhouse gas that it cannot be counted as one at any levels above 200 ppm. THE "greenhouse gas" is H2O in its three phases that exist in the atmosphere. Nothing else in the quantities available is 100th the levels that H2O is. Any increases in CO2 above 200 ppm has no corresponding effect on temperature slowing of radiant energy.

No gas or vapor is capable of warming the Earth using light emitted from the surface, Wake. See the 1st and 2nd laws of thermodynamics and the Stefan-Boltzmann law.
Wake wrote:
What's more, there is so much humbuggery about the several gases that can absorb IR that the people making claims about these should be held up to public ridicule at every opportunity.

Absorption of surface emitted IR does not warm the Earth, Wake. I am holding you up to public ridicule, as you requested.


The Parrot Killer




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