"A better, richer and happier life for all our citizens." That's the American dream. In practice, it means living in a spacious, air-conditioned house, owning a car or three and maybe a boat or a holiday home, not to mention flying off to exotic destinations.
The trouble with this lifestyle is that it consumes a lot of power. If everyone in the world started living like wealthy Americans, we'd need to generate more than 10 times as much energy each year. And if, in a century or three, we all expect to be looked after by an army of robots and zoom up into space on holidays, we are going to need a vast amount more. Where are we going to get so much power from?
It is clear that continuing to rely on fossil fuels will have catastrophic results, because of the dramatic warming effect of carbon dioxide. But alternative power sources will affect the climate too. For now, the climatic effects of "clean energy" sources are trivial compared with those that spew out greenhouse gases, but if we keep on using ever more power over the coming centuries, they will become ever more significant.
While this kind of work is still at an early stage, some startling conclusions are already beginning to emerge. Nuclear power - including fusion - is not the long-term answer to our energy problems. Even renewable energies such as wind power will have to be used with caution, because large-scale extraction could have both local and global effects. These effects are not necessarily a bad thing, though. We might be able to exploit them to geoengineer the climate and combat global warming.
There is a fundamental problem facing any planet-bound civilisation, as Eric Chaisson of the Harvard Smithsonian Center for Astrophysics in Cambridge, Massachusetts, points out. Whatever you use energy for, it almost all ends up as waste heat.
Much of the electrical energy that powers your mobile phone or computer ends up heating the circuitry, for instance. The rest gets turned into radio waves or light, which turn into heat when they are absorbed by other surfaces. The same is true when you use a mixer in the kitchen, or a drill, or turn on a fan - unless you're trying to beam radio signals to aliens, pretty much all of the energy you use will end up heating the Earth.
We humans use a little over 16 terawatts (TW) of power at any one moment, which is nothing compared with the 120,000 TW of solar power absorbed by the Earth at the same time. What matters, though, is the balance between how much heat arrives and how much leaves (see "Earth's energy budget") . If as much heat leaves the top of the atmosphere as enters, a planet's temperature remains the same. If more heat arrives, or less is lost, the planet will warm. As it does so, it will begin to emit more and more heat until equilibrium is re-established at a higher temperature.