This is (mostly) true, but the reason for it may not be clear to everyone. Let’s cover some basic thermodynamics:
[ol][li]In any process, the total energy of an isolated (adiabatic) system remains constant.[/li][li]No process can generate as much usable work as the thermodynamic energy that is input.[/li][li]As the temperature of the system becomes uniform, entropy is maximized.[/ol][/li]Heat is kinetic energy, just like a cannon ball, a lever and fulcrum, or a spinning flywheel. However, heat differs from these processes in that it is stochastic and has no inherent direction or vector. In order to extract heat, you have to direct its motion by creating a low temperature or low pressure region that it will flow toward. (Temperature and pressure are two components of the same concept (as expressed in the ideal gas law). Doing so allows you to use said motion to operate a heat engine, converting some of the thermal energy into mechanical work, at the cost of increasing entropy. (See Law #2). This increase in entropy is represented as the “smoothing out” of thermal differences (Law #3). In a closed system, or (in our particular case) one which has a maximum thermal throughput, anything you do beyond that throughput rating from within the system makes no difference; you’re still adding more heat that can be extracted.
The radiating energy via laser to space concept proposed by si_blakely is, technically, a way of increasing the emissivity to space. However, in order to operate this laser, you’re going to have to convert heat–which again, has no intrinsic preferred direction–to coherent light, which is highly directional and organized. Not only is this decrease in entropy going to require corresponding increases in entropy elsewhere in the system, but the heat engine process(es) you are going to have to perform in order to direct the energy is going to create even more entropy and waste heat. So, you’re creating more heat in order to direct the existing waste heat out to space.
Let’s say, for instance, that you’re going to use a thermal differential to drive a Stirling cycle engine (which, along with the Ericsson cycle is theoretically one of the most thermodynamically efficient heat engines with a real world application), the Stirling drives a dynamo, the dynamo charges up large banks of capacitors which in turn couple into a charged medium which excites electrons, pumping them up to an excited state from which they fall and emit photons of specific direction/orientation, frequency, and phase by stimulated emission. Each of these stages will have a certain, under-unity efficieny. Unless the compound product of all these efficiences exceeds the natural emissivity of the Earth, there’s no benefit to it. Even if it does demonstrate positive efficiency, you are relying on the use of natural thermal gradients to drive your heat engine; unless the low temperature reservoirs are effictively infinite in thermal mass (that is to say, they can absorb the waste heat indefinitely without increasing in temperature) you are using a limited resource to permit your heat engine to function; once you get close to “evening out” the heat distribution, i.e. achieved maximum entropy, your process will break down.
In short, it’s not a feasible solution for the problem of global heat saturation.
But you notice that the bulk of smog-producing processes (save for the inescabable automobile) have, in fact, moved out of urban areas as transportation has become cheaper. I would similiarly expect that, given an ability to perform heavy industry and energy production off-planet, there would be an impetus to minimize the impact on the habitat where people want to live.
Stranger