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Old 10th July 2010, 07:01 AM   #67
Critical Thinker
Join Date: Apr 2007
Posts: 334
Originally Posted by macdoc View Post
Read the second paragraph from the link above

You should tutor those who actually need further education of the basics.

From your reference:
"Figure 1: The shortwave rays from the sun are scattered in a cloud. Many of the rays return to space. The resulting cloud albedo forcing, taken by itself, tends to cause a cooling of the Earth."
To my remark
"The high albedo on Venus is due to its clouds"
CapelDodger responded:
"Yes, and irrelevant. Solar radiation that is reflected away from Venus does not influence its temperature." (#54)
To Warming Early Mars with Carbon Dioxide Clouds That Scatter Infrared Radiation he objected:
"Irrelevant, since scattering is very different from reflection." (#63)
By the way, clouds do reflect (or scatter back) thermal radiation. A quote from Longwave Multiple Scattering in Clouds: Climatic Implications:
"In most global climate models, the multiple scattering of longwave radiation by particles like clouds has been neglected. As the single scattering albedoes of both ice and water clouds are between 0.4 to 0.7, the mutipple scattering of longwave radiation by cloud droplets increases the effective absorption path length."
Or from Longwave multiple scattering by clouds:
" and the albedo R increases monotonically with optical depth. Of note in the thermal part of the spectrum is the rather large reflectivity exhibited in the 10 20 μm region by the smaller size (5μm) particles which shifts toward longer wavelengths for larger (25μm) particles. Accordingly, a substantial amount of longwave radiation is reflected by clouds reducing the cirrus emissivity at these wavelengths by a (1 R) factor."
Originally Posted by macdoc View Post
Do you understand the difference between inside the box reflections which you discuss and albedo reflection in the long wave IR range?

Can your question be interpreted as more than a coward insinuation?

Let us assume a planet with fully transparent atmosphere and a universal cloud deck. Then a thermal-radiation cloud-albedo of 100% would mean that the cloud deck reflects (i.e. scatters back) the whole thermal surface radiation, resulting in no heat loss of the surface by thermal radiation.

And a cloud-albedo of 70% would mean, that at every moment, 70% of the amount of emitted thermal radiation comes in from the cloud deck. This obviously entails that the heat loss of the surface by thermal radiation is reduced by 70%.

Anyway, I should return to the essential, and avoid pointless sideshow quarrels.


Sometimes the wrong is more instructive than the right
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