Darth Entropy eats the Space Cadets' lunch

The Breakdown Institute is quite famous for wanting us to wait for pie in the sky by and by, and indeed, their link to the Space Cadets of the Marshall institute is the Manchurian Senior Fellow Marty Hoffert whose reason for existing is space based power generation. The Marshall Institute likes this because there is a great deal of dual use technology linking space based power generation with Star Wars.

Darth Entropy, in the person of Eric Chaisson (arguably an opponent of Star Wars) points out that space based power generation is not a free lunch and he is not even talking about the cost of setting the system up. As he writes in a recent edition of EOS (the house journal of the American Geophysical Union. Join already, it's a bargain), power density in the universe has been increasing since the year dot, and a lot more since thee and me arrived on the scene.


As all young bunnies know, power in is soon reduced to heat out. If we get our power from the sun, then it comes in as thermal, goes out as thermal and we glom a bit of it off to do useful work. According to Chaisson, our prehistorical ancestors used about 0.05 kilowatts each, agriculture raised that by a factor of 10 and the average person on earth today uses about 2.5 KW. OTOH USAian bunnies use about another factor of five more, or 12.5 KW each.

The sun shines about 120,000 terrawatts on the Earth, and today we use about 18 TW(~0.015% of solar), but if you assume that everyone will reach the US standard usage and that population will grow to 9 billion, and throw a bit of growth of usage from 12.5 KW in you get about 100 TW (~0.08% of solar) for global power demand in the not so far future, say 2100. Any sources of energy except solar thus will contribute an extra heat load, which will raise the global temperature as surely as increasing CO2 would. The major difference would be that the CO2 heat load accumulates, e.g. once injected imposes a significant forcing over centuries, while the power dissipation heat load goes away as soon as civilization collapses from heat stroke or a bit longer as the satellites fall out of the sky on a new generation of hunter gatherers.

The addition of heat from fossil fuel derived, nuclear and fusion energy can be thought about in a straightforward manner. Space derived energy OTOH heats the Earth by effectively raising the amount of solar insolation. This, of course, is one of the things that has held back construction of Dyson spheres, where do you dump the heat load?

It takes about 4800 TW to raise the temperature of the Earth ~3 K (these are Chaisson's numbers, Eli is too lazy to calculate his own). Assuming energy equality at the high end reached by the mid-2100s and 1% growth in power needs thereafter, there would be a 3 K rise in global temperature in about three centuries or, thanks to the power of compound interest and economics, a 10 K rise in 450 years. It goes a lot faster, of course, if you are simultaneously raising the amount of greenhouse gases in the atmosphere.

As in most such things, assumptions about growth are driving this, still anyone claiming to think big and long should take it into account.