RE: More on global warming, etc

["Dukelow, James S Jr" <jim.dukelow@PNL.GOV>]

See response below:

-----Original Message-----

From: Michael McNaughton [mailto:mcnaught@LANL.GOV]

Sent: Thursday, April 26, 2001 6:44 AM

To: RuthWeiner@AOL.COM; radsafe@list.vanderbilt.edu

Subject: Re: More on global warming, etc





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



=================



Mike,



I understand Ruth to be asking a different question than the one you answered.

I believe she asked if the long-wave energy absorbed by CO2 and other greenhouse

gases is somehow preferentially re-radiated back toward the earth's surface.



The answer to that question is "No".  The reemission from CO2, etc. is

isotropic, so roughly half of the emitted photons will be directed downward,

tending to warm the earth's surface.



To give the physicist's something to shoot at, a first-order energy balance

might look like:



Long-wave energy emitted from surface = Q = Q1 + Q2, where Q1 passes through the

atmosphere unabsorbed to deep space, Q2 is absorbed and alpha*Q2 re-emitted with

0.5*alpha*Q2 directed downward.



Now suppose everything is unchanged except that concentrations of greenhouse

gases have increased, absorbing an additional quantity, df, of long-wave energy.

Now the balance is 



Q = (Q1 - df) + (Q2 + df)



and  0.5*alpha*(Q2 + df) is re-emitted directed downward and available for

warming the surface.  In this case, there is an additional amount of energy,

0.5*alpha*df, available to warm the surface. 



A full equilibrium analysis would have to pursue 1) the effect of the warming of

the surface on Q, 2) the effect of absorption at different levels in the

atmosphere on alpha, and 3) the effect of multiple absorptions in the atmosphere

on the value 0.5 for the fraction of re-emitted energy directed downward, on

convergence to a new energy balance.  What's probably more relevant for the

current situation is a transient analysis, considering energy storage in land,

ocean, and atmosphere, with resultant impact on temperature and climate futures,

in general.  Perhaps more than coincidently, that's what the coupled general

climate models are trying to do.



Best regards.



Jim Dukelow

Pacific Northwest National Laboratory

Richland, WA

jim.dukelow@pnl.gov



These comments are mine and have not been reviewed and/or approved by my

management or by the U.S. Department of Energy.

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