Re: More on global warming, etc

[DWhitfil@KDHE.STATE.KS.US]

Here is a fairly simple explanation from

http://liftoff.msfc.nasa.gov/academy/space/greenhouse.html:

                                                                

 Greenhouse gases-carbon dioxide, methane, nitrous oxide, and   

 others-are transparent to certain wavelengths of the Sun's     

 radiant energy, allowing them to penetrate deep into the       

 atmosphere or all the way to Earth's surface. Clouds, ice      

 caps, and particles in the air reflect about 30 percent of     

 this radiation, but oceans and land masses absorb the rest,    

 then release it back toward space as infrared radiation. The   

 greenhouse gases and clouds effectively prevent some of the    

 infrared radiation from escaping; they trap the heat near      

 Earth's surface where it warms the lower atmosphere. If this   

 natural barrier of atmospheric gases were not present, the     

 heat would escape into space, and Earth's mean global          

 temperatures could be as much as 33 degrees Celsius cooler     

 [about -18 degrees Celsius as opposed to 15 degrees Celsius].  

                                                                







Here is another amongst the myriad found at

http://www.royal.okanagan.bc.ca/mpidwirn/atmosphereandclimate/greenhouse.html#b:



As energy from the sun passes through the atmosphere a number of things

take place (see Figure). A portion of the energy (26 % globally) is

reflected back to space by clouds and particles. About 19 % of the energy

available is absorbed by clouds, gases (like ozone), and particles in the

atmosphere. Of the remaining 55 % of the solar energy passing through the

Earth's atmosphere, 4 % is reflected from the surface back to space. On

average about 51 % of the sun's radiation reaches the surface. This energy

is then used in number of processes including: the heating of the ground

surface; the melting of ice and snow and the evaporation of water; and

plant photosynthesis.



The heating of the ground by sunlight causes the Earth's surface to become

a radiator of energy in the longwave band (sometimes called infrared

radiation). This emission of energy is generally directed to space (see

Figure). However, only a small portion of this energy actually makes it

back to space. The majority of the outgoing infrared radiation is absorbed

by a few naturally occurring atmospheric gases known as the greenhouse

gases. Absorption of this energy causes additional heat energy to be added

to the Earth's atmospheric system. The now warmer atmospheric greenhouse

gas molecules begin radiating longwave energy in all directions. Over 90 %

of this emission of longwave energy is directed back to the Earth's surface

where it once again is absorbed by the surface. The heating of the ground

by the longwave radiation causes the ground surface to once again radiate

repeating the cycle described above, again and again, until no more

longwave is available for absorption.



DJWhitfill



Opinions expressed are mine and do not reflect official policies or

positions of the Kansas Department of Health and Environment.





                                                                                                                             

                    Michael McNaughton                                                                                       

                    <mcnaught@LANL.GOV>            To:     RuthWeiner@AOL.COM, radsafe@list.vanderbilt.edu                   

                    Sent by:                       cc:                                                                       

                    owner-radsafe@list.vand        Subject:     Re: More on global warming, etc                              

                    erbilt.edu                                                                                               

                                                                                                                             

                                                                                                                             

                    04/26/01 08:43 AM                                                                                        

                    Please respond to                                                                                        

                    Michael McNaughton                                                                                       

                                                                                                                             

                                                                                                                             









At 09:13 AM 4/26/01 -0400, RuthWeiner@AOL.COM wrote:

>  Is the "global warming" effect

>preferential re-radiation back to the earth's surface, and if so, why?



Yes, because the spectrum (of photon energies) is different. The spectrum

is a Maxwell-Boltzmann distribution that depends on the temperature of the

radiating object. The earth is cooler than the sun so the photons radiated

by the earth have a lower energy than those from the sun.



mike

Mike McNaughton

Los Alamos National Lab.

email: mcnaught@LANL.gov or mcnaughton@LANL.gov

phone: (505)667-6130



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