Hi Robin, ----- Original Message ----- From: "Robin van Spaandonk" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Sunday, August 13, 2006 4:20 AM Subject: Re: [Vo]: Re: Ratio of solar to manmade energy > In reply to Michel Jullian's message of Sun, 13 Aug 2006 02:58:42 > +0200: > Hi, > [snip] >>That's what I said, "unlimited cheap energy of non solar origin for the >>masses will necessarily promote global warming", but I had no idea the effect >>was that significant! The tenfold increase in global energy consumption you >>evoke would only mean >>1.2E14/1E10 W = 12 kW >>for each of the ~10 billion humans the planet will bear in a few years, >>that's about the consumption per average US citizen _today_ isn't it? >> >>It seems this is a real problem. Have you worked out the amplitude of the >>global temperature increase in this scenario? > > First, even a ten fold increase in energy use would only equal > 1/1000 of the normal solar flux,
agreed > so our influence would be minor. > In the second instance, this is compensated for by an increase in > temperature resulting in an increase in radiation. indeed thermal equilibrium implies that radiated power is equal to collected + generated power, so a 1/1000 increase in the latter results in a 1/1000 inscrease in the former > Since radiation > goes as the fourth power of temperature, right, Stefan-Boltzmann law P=Constant*T^4, cf http://en.wikipedia.org/wiki/Black_body > even an extremely small > increase in temperature would be enough to dump the excess energy. > (If memory serves, and I didn't get the arithmetic wrong the first > time around, about 1/50 ºC would suffice). Let's see, P=Constant*T^4 => dP/dT=4*Constant*T^3=4*P/T => dT=dP*T/(4*P)=(dP/P)*T/4 In the present scenario DP/P=1/1000 and T ~= 300K so dT ~= 300/4000 = 0.075 °C i.e. about 4 times your estimate if I got it right, even so it is much smaller than the ~6°C global cooling due to elimination of greenhouse gases by converting to CF (or any nuclear energy) as you said, so it's not a problem in fact. Even a 100 fold increase in primary energy use would be OK if we switch to all-nuke , as it would only raise global temp by 10*0.075 °C = 0.75°C. It would take a 1000 fold increase roughly for the P increase warming to compensate the CO2 decrease cooling (about 6°C). Michel
