In today's catastrophic risks and resilience seminar, perhaps the most disturbing presentation was by J. Storrs (Josh) Hall, who gave a talk on “The Weather Machine: Nano-enabled Climate Control for the Earth.”
Josh offered a simple proposition: once molecular manufacturing is achieved, it should not be difficult to create a design so a nanofactory can produce a tiny transparent balloon fitted with GPS and radio (for sending data and receiving instructions) and a simple set of thrusters to maintain location and to control altitude.
So far, so good. But there are a few additions to this balloon that make its impacts pretty wild: first, it includes a mirror to be used either for reflecting sunlight back into space or directing it to a solar energy collector on earth; second, the mirror can be turned as instructed; and third, because the balloon is made by a nanofactory, as many of them as desired can produced and put into operation in a very short time.
Basic calculations suggest that, in maybe a week or less, ten million tons of raw materials could produce enough balloons to cover the entire earth at twenty miles altitude. That may sound like a lot of material, but in fact it's about the same amount that goes into building 100 miles of a modern highway -- so it's well within reach of even a small nation to acquire the materials if they have the hardware and software and a desire to control the weather of the earth.
Shifting mirrors inside balloons to make some areas warmer and others colder, to make some wetter and some drier gives at least rudimentary power for Josh's "Nano-enabled Climate Control for the Earth." These balloons may well be helpful in slowing, stopping, or even reversing the trend of global warming, as long as we recognize the very real danger of unforeseen, unintended, and possibly irreversible consequence.
Of course, having the means to control weather also allows controlling agricultural production, by improving or degrading climate conditions in growing areas. That implies using the balloons as a form of friendship or for hostile intent -- not to mention that aiming a set of mirrors at a city could instantly annihilate it.
However the capability is used, if the simple manufacture and deployment of a basically low-tech thing like a bunch of balloons can provide enough power to totally dominate the earth, then it seems we're only beginning to understand the implications of advanced nanotechnology.