Post by northsphinx on Jun 17, 2009 23:21:13 GMT
There is a strong greenhouse effect even without greenhouse gasses.
I will here show why.
If the atmosphere where made of pure nitrogen without ANY vapor or any CO2 would the earth still be heated by the sun and the earth be cooled by the radiation heat balance to space..
Nitrogen is largely transparent to infrared and visible radiation. I make the assumption that it is completely transparent to ANY radiation. The atmosphere would not be heated or cooled by ANY radiation.
But there would be wind and convection due to temperature differences.
With a complete dry air would the temperature in the atmosphere try to follow the adiabatic lapse rate
en.wikipedia.org/wiki/Adiabatic_lapse_rate
A temperature decrease by about 10 K/km in altitude.
If now the rising sun start to heat the ground will there be wind. A wind that slow the heating of the surface because of heat transfer by convection to the atmosphere. The heated air will be rising because of the changed density. The surface will not be as hot as without any atmosphere in the evening. But it will have absorbed about the same amount of solar energy at the end of the day. The atmosphere will be heated by convection.
Cooling during night is very different.
The earth will see a cold space and drive heat out in space with radiation. Temperature difference will be surface temperature and temperature of empty space, say 1K. Between these two temperatures will a lot of heat be radiated.
But what will happened during cooling with the nitrogen atmosphere? The only way this can loose heat is by convection back to earth. Air cooled by the surface during the night will not rise because the air above is warmer. The wind will die out at night. As on planet earth now. This atmosphere is working as diode for heat. The surface cools just because of radiation not by convection during night.
Next day will the ground be heated again but now without wind until the surface is capable to make the air close to the surface warmer than the air above so the wind start again. A cooling wind from the surface perspective start little later the next day .
But the air temperature is higher than the previous day since the air is not cooled efficient by the surface during nights without wind.
This will result in a warmer airmass than average surface temperature.
A natural greenhouse effect for the atmosphere without any vapor or CO2.
How much warmer?
The atmosphere will approximately be in balance when it reach the average surface afternoon temperature with a adjustment for the adiabatic lapse rate for altitude. That would be very much in a atmosphere without latent heat and low heat capacity of the ground.
Example with the worst example, a earth with 100% water as surface:
When the water is heated by direct Sunshine in the upper water levels will the warmer water rise to the surface and induce a movement in the water body. Without any wind will this be very stable and not deep. Most energy is absorbed in the top level of water because hot water rise and stay at the surface.
If the surface get hot enough will the atmospheric convection start and a wind will occur.
Energy is passed over to the air and heat the atmosphere. By convection. And the atmosphere will still became warmer than the oceans as showed before after a time.
During night will radiation cool the surface and the top layer will sink according to its density.
Since it is cooled and heated from above will the daily temperature fluctuations depend on the thickness of mixed water which is depending on wind speed.
BUT we have seasons at earth.
This will make the atmosphere locally try to become as hot as the hottest period since it is not cooled efficiently. No outgoing infrared radiation from the atmosphere itself and little night wind for convection will make the atmosphere ending up in summer temperature maximums as the average temperatures.
The largest impact will this of course have on higher latitudes.
The atmosphere would be significant warmer than the ground with an IR inert atmosphere.
A green house effect without green house gasses.
And with vapor and CO2 in the atmosphere?
The CO2 and vapor cant have another temperature than the air it is in. That mean if these gases absorbs any heat by radiation will the air around it use that energy and heat itself. It is impossible to have some hotter gases inside a airmass. The temperature will be equaled. The radiation cant miss the first km of CO2 in the atmosphere and then all of a sudden find some low temperature CO2.
Temperature difference 10 K/km or 0,01 K/m for dry air inside the atmosphere is not sufficient to drive any significant heat flux by radiation through the air levels. Not with an atmosphere that absorb any heat by radiation.
It will work from the ”top” of atmosphere against cold space with that big temperature differences. But not inside a atmosphere between air masses with similar temperatures that absorbs and emits heat.
Basic.
The implication is that the cloud free atmosphere hardly absorb any heat by radiation to allow any the earths surface radiation to escape at the top of the atmosphere into cold space. And the heat needed to keep the temperature at the top of the atmosphere is not lifted by radiation .
Is the cloud free atmosphere absorbing any heat?
It it easy to measure the temperature signature of a cloud free sky at night in dry climate.
It is a very low temperature. The cloud free dry atmosphere absorbs very little heat.
But how can the atmosphere keep the lapse rate temperature drop with altitude without absorbing heat?
The gas temp follow the temperature of the lapse rate formula in height. The temperature inside the atmosphere are kept high despite a very low absorption. This shows clearly that the heat must be lifted by something else than radiation. That is convection by instable air. Not by radiation. The radiation temperature from tropopause is set by the lapse rate convection within the troposphere.
Despite how much the IR radiation the atmosphere itself absorb.
Does it matter if the atmosphere absorbs all radiated IR?
Lets assume we increase the amount of CO2 up to that we achieve 100% absorption.
Which effect would that have? It would be from IR perspective as fog. But as previously showed will the temperature gradient in the troposphere still be following the atmosphere lapse rate. The heat will still go up wards by convection and only convection. The radiation out in space will still be from top of the atmosphere but since cooling will be from ”above” instead from the surface will the atmosphere NOT be warmer than the ground. The natural green house effect will be lost.
The heat balance for earth will only be set by radiation from the top of the atmosphere temperature instead of radiation set by the average ground temperature. But without the warmer atmosphere relative to surface by the natural green house.
The earth surface temperature will be more even but average probably not higher because this effects balance each other very well.
Vapor, clouds, rain and snow will with its latent heat have a large impact of redistributing energy in place and time.
It is all about the clouds.
I will here show why.
If the atmosphere where made of pure nitrogen without ANY vapor or any CO2 would the earth still be heated by the sun and the earth be cooled by the radiation heat balance to space..
Nitrogen is largely transparent to infrared and visible radiation. I make the assumption that it is completely transparent to ANY radiation. The atmosphere would not be heated or cooled by ANY radiation.
But there would be wind and convection due to temperature differences.
With a complete dry air would the temperature in the atmosphere try to follow the adiabatic lapse rate
en.wikipedia.org/wiki/Adiabatic_lapse_rate
A temperature decrease by about 10 K/km in altitude.
If now the rising sun start to heat the ground will there be wind. A wind that slow the heating of the surface because of heat transfer by convection to the atmosphere. The heated air will be rising because of the changed density. The surface will not be as hot as without any atmosphere in the evening. But it will have absorbed about the same amount of solar energy at the end of the day. The atmosphere will be heated by convection.
Cooling during night is very different.
The earth will see a cold space and drive heat out in space with radiation. Temperature difference will be surface temperature and temperature of empty space, say 1K. Between these two temperatures will a lot of heat be radiated.
But what will happened during cooling with the nitrogen atmosphere? The only way this can loose heat is by convection back to earth. Air cooled by the surface during the night will not rise because the air above is warmer. The wind will die out at night. As on planet earth now. This atmosphere is working as diode for heat. The surface cools just because of radiation not by convection during night.
Next day will the ground be heated again but now without wind until the surface is capable to make the air close to the surface warmer than the air above so the wind start again. A cooling wind from the surface perspective start little later the next day .
But the air temperature is higher than the previous day since the air is not cooled efficient by the surface during nights without wind.
This will result in a warmer airmass than average surface temperature.
A natural greenhouse effect for the atmosphere without any vapor or CO2.
How much warmer?
The atmosphere will approximately be in balance when it reach the average surface afternoon temperature with a adjustment for the adiabatic lapse rate for altitude. That would be very much in a atmosphere without latent heat and low heat capacity of the ground.
Example with the worst example, a earth with 100% water as surface:
When the water is heated by direct Sunshine in the upper water levels will the warmer water rise to the surface and induce a movement in the water body. Without any wind will this be very stable and not deep. Most energy is absorbed in the top level of water because hot water rise and stay at the surface.
If the surface get hot enough will the atmospheric convection start and a wind will occur.
Energy is passed over to the air and heat the atmosphere. By convection. And the atmosphere will still became warmer than the oceans as showed before after a time.
During night will radiation cool the surface and the top layer will sink according to its density.
Since it is cooled and heated from above will the daily temperature fluctuations depend on the thickness of mixed water which is depending on wind speed.
BUT we have seasons at earth.
This will make the atmosphere locally try to become as hot as the hottest period since it is not cooled efficiently. No outgoing infrared radiation from the atmosphere itself and little night wind for convection will make the atmosphere ending up in summer temperature maximums as the average temperatures.
The largest impact will this of course have on higher latitudes.
The atmosphere would be significant warmer than the ground with an IR inert atmosphere.
A green house effect without green house gasses.
And with vapor and CO2 in the atmosphere?
The CO2 and vapor cant have another temperature than the air it is in. That mean if these gases absorbs any heat by radiation will the air around it use that energy and heat itself. It is impossible to have some hotter gases inside a airmass. The temperature will be equaled. The radiation cant miss the first km of CO2 in the atmosphere and then all of a sudden find some low temperature CO2.
Temperature difference 10 K/km or 0,01 K/m for dry air inside the atmosphere is not sufficient to drive any significant heat flux by radiation through the air levels. Not with an atmosphere that absorb any heat by radiation.
It will work from the ”top” of atmosphere against cold space with that big temperature differences. But not inside a atmosphere between air masses with similar temperatures that absorbs and emits heat.
Basic.
The implication is that the cloud free atmosphere hardly absorb any heat by radiation to allow any the earths surface radiation to escape at the top of the atmosphere into cold space. And the heat needed to keep the temperature at the top of the atmosphere is not lifted by radiation .
Is the cloud free atmosphere absorbing any heat?
It it easy to measure the temperature signature of a cloud free sky at night in dry climate.
It is a very low temperature. The cloud free dry atmosphere absorbs very little heat.
But how can the atmosphere keep the lapse rate temperature drop with altitude without absorbing heat?
The gas temp follow the temperature of the lapse rate formula in height. The temperature inside the atmosphere are kept high despite a very low absorption. This shows clearly that the heat must be lifted by something else than radiation. That is convection by instable air. Not by radiation. The radiation temperature from tropopause is set by the lapse rate convection within the troposphere.
Despite how much the IR radiation the atmosphere itself absorb.
Does it matter if the atmosphere absorbs all radiated IR?
Lets assume we increase the amount of CO2 up to that we achieve 100% absorption.
Which effect would that have? It would be from IR perspective as fog. But as previously showed will the temperature gradient in the troposphere still be following the atmosphere lapse rate. The heat will still go up wards by convection and only convection. The radiation out in space will still be from top of the atmosphere but since cooling will be from ”above” instead from the surface will the atmosphere NOT be warmer than the ground. The natural green house effect will be lost.
The heat balance for earth will only be set by radiation from the top of the atmosphere temperature instead of radiation set by the average ground temperature. But without the warmer atmosphere relative to surface by the natural green house.
The earth surface temperature will be more even but average probably not higher because this effects balance each other very well.
Vapor, clouds, rain and snow will with its latent heat have a large impact of redistributing energy in place and time.
It is all about the clouds.
