Now levels of greenhouse gases are rising, and roughly 380 TW less heat is escaping. Over the past few thousand years, Earth was roughly in equilibrium and the climate changed little. As it does so, it will begin to emit more and more heat until equilibrium is re-established at a higher If more heat arrives, or less is lost, the planet will warm. If as much heat leaves the top of the atmosphere as enters, a planet’s temperature remains the same. What matters, though, is the balance between how much heat arrives and how much leaves (see “Earth’s energy budget”). 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. 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. The rest gets turned into radio waves or light, which turn into heat when they are absorbed by other surfaces. Much of the electrical energy that powers your mobile phone or computer ends up heating the circuitry, for instance. Whatever you use energy for, it almost all ends up as waste heat. 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. We might be able to exploit them to geoengineer the climate and combat global warming. These effects are not necessarily a bad thing, though. 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. Nuclear power – including fusion – is not the long-term answer to our energy problems. While this kind of work is still at an early stage, some startling conclusions are already beginning to emerge. 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. But alternative power sources will affect the climate too. It is clear that continuing to rely on fossil fuels will have catastrophic results, because of the dramatic warming effect of carbon dioxide.
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