Version One: 1000 Times More Powerful than Global Warming
You build a little balloon—my guess is the balloon needs to be somewhere between a millimeter and a centimeter in size. It has a very thin shell of diamond, maybe just a nanometer thick. It’s round, and it has inside it an equatorial plane that is a mirror. If you squished it flat, you would only have a few nanometers thick of material. Although you could build a balloon out of materials that we build balloons out of now, it would not be economical for what I’m going to use it for.
Given that we can build these balloons so that the total amount of material in a balloon is actually very, very small, you inflate them with hydrogen in such a way that they will stabilize about twenty miles up in the stratosphere. So you have these itty bitty balloons, and inside of them they have a mirror. They also have a tiny little control unit and just barely enough power, fans, or other actuators to tilt themselves to a preferred orientation. Now you make enough of them to cover the entire globe.
This is why the nanotechnology makes a big difference, because if they are as thick as I have described them, you only need about ten million tons of material to do that. To compare that with the stuff that we are used to, that is about the same amount of material that is used to make a hundred miles of freeway. This is nothing that our technology cannot handle, assuming that you can actually turn it into a high-tech gadget of the kind I described.
So you have this balloon and it floats up there twenty miles. They all have a little GPS and receiver so they can turn themselves. That’s all there is to it. What can you do with a machine like this? The machine is essentially a programmable greenhouse gas. If you set the mirrors facing the sun, it reflects all the sunlight back. If you set them sideways, it allows the sunlight to come through, and similarly for the longwave radiation coming from the back side of the earth at night.
This machines, which I call “the weather machine,” has a radiative forcing capability. For comparison, the radiative forcing capability for CO2, as generally mentioned in the global warming theories, is about one watt per square meter. This machine essentially has a kilowatt per square meter of radiative forcing capability. It completely trumps any natural influence of that kind that’s out there or that we can imagine. If you are worried about our world dying because of global warming, or if you are one of the people who is worried about our world falling into an ice age, we can fix that.
Version Two: Absorb/Transmit Any Frequency, Direction and Phase
You have the same balloon, but inside of it you have a kind of aerogel that is switchable antenna units with crosslinks. You can tune the thing to be an absorber or transmitter of radiation in any desired frequency, in any desired direction (and if you’re really good, with any desired phase).
Once you get that, essentially you’ve turned this layer in the stratosphere into an enormous hologram. Of course, the astronomers really hate it, because it screws up viewing, but what they do love is that it turns the entire earth into a telescope with the aperture of 8,000 miles. Of course, you can take that light and change it into any other wavelength you want and send it off into any other direction you want. You can control not only the climate as a single parameter, but you can probably get close to controlling local weather. We don’t come close to knowing enough about the whole weather system to say exactly what you could and couldn’t do, but I am fairly sure that you could do things like make Canada as warm as California. You could cool the tropics, you could warm up the polar regions if you wanted to.
Collecting the Concentrated Solar Power
If you wanted to use solar power, for example, you could build an array of photovoltaics out in the desert out there somewhere and you could take the area of about a thousand square kilometers above it and set the little mirrors in the first version, or charge your little antennas in the second, to focus the sunlight down onto your area. Instead of having to have a thousand square kilometers of solar collectors, you have one. You have just concentrated all that sunlight on it and it’s pretty much free, because you have already built a device to control the weather. What’s more, you have not changed the energy balance any, because you are shading all the areas that are otherwise under the thousand square kilometers. That gives you in broad daylight an energy flux that is approximately the same as a thousand nuclear reactors of a typical size. Of course, you have to cool the collectors fairly vigorously because they are not 100% efficient.
Full Kardashev Type I by Definition
You would be able to use all of the solar power hitting the earth. Once the collectors are built underneath then earth would be a full Kardashev Type I civilization.
Type I — a civilization that is able to harness all of the power available on a single planet. Earth has an available power of 1.74 ×10**17 W (174 petawatts).
Current world energy usage and generation is at about 17 terawatts. Getting all solar power means about 2000-5000 times current power levels. You still have to convert to electricity which is not perfectly efficient and solar energy still needs to go into the earth for normal biosphere processes.
If your nanotechnology is at this level then making spaceships and sending nanofactories to Venus and asteroids would be relatively simple. It would be about twenty million tons of material for the mirror bubbles and converters for each earth scale energy system. Then the electricity has to be transmitted and distributed to where it needs to be used (a super-grid which could be wireless)
Two billion of those systems turns humanity into a Kardashev Type II civilzation.
Type II — a civilization that is able to harness all of the power available from a single star, approximately 3.86 ×10**26 W.
40,000 trillion tons of nanotechnology produced material (mostly nanometer thick shells of millimeter to centimeter size filled with aerogel and some electronics) enables a Kardashev Type II civilization.
An earth type I civilization makes use of roughly 25 megatons of TNT equivalent a second. Sol type II civilization consumes 2 billion times more energy.
A civilization that controls thousands (type I) to a trillion times (type II) more power than our current civilization would have a lot of power for good or for destruction.
Update: for space based collection There was the Devon Crowe idea of large space bubbles cured by ultraviolet. Large space bubbles could be adapted for concentrating solar power with lightweight structures.