What does the word "renewable" mean?
Last week the Intergovernmental Panel on Climate Change released a thousand-page report on the future of renewable energy, which it defined as solar, hydro, wind, tidal, wave, geothermal and biomass. These energy sources, said the IPCC, generate about 13.8% of our energy and, if encouraged to grow, could eventually displace most fossil fuel use.
It turns out that the great majority of this energy, 10.2% out of the 13.8% share, comes from biomass, mainly wood (often transformed into charcoal) and dung. Most of the rest is hydro; less than 0.5% of the world's energy comes from wind, tide, wave, solar and geothermal put together. Wood and dung are indeed renewable, in the sense that they reappear as fast as you use them. Or do they? It depends on how fast you use them.
One of the greatest threats to rain forests is the cutting of wood for fuel by impoverished people. Haiti meets about 60% of its energy needs with charcoal produced from forests. Even bakeries, laundries, sugar refineries and rum distilleries run on the stuff. Full marks to renewable Haiti, the harbinger of a sustainable future! Or maybe not: Haiti has felled 98% of its tree cover and counting; it's an ecological disaster compared with its fossil-fuel burning neighbor, the Dominican Republic, whose forest cover is 41% and stable. Haitians are now burning tree roots to make charcoal.
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You can likewise question the green and clean credentials of other renewables. The wind may never stop blowing, but the wind industry depends on steel, concrete and rare-earth metals (for the turbine magnets), none of which are renewable. Wind generates 0.2% of the world's energy at present. Assuming that energy needs double in coming decades, we would have to build 100 times as many wind farms as we have today just to get to a paltry 10% from wind. We'd run out of non-renewable places to put them.
You may think I'm splitting hairs. Iron ore for making steel is unlikely to run out any time soon. True, but you can say the same about fossil fuels. The hydrocarbons in the earth's crust amount to more than 500,000 exajoules of energy. (This includes methane clathrates—gas on the ocean floor in solid, ice-like form—which may or may not be accessible as fuel someday.) The whole planet uses about 500 exajoules a year, so there may be a millennium's worth of hydrocarbons left at current rates.
Contrast that with blue whales, cod and passenger pigeons, all of which plainly renew themselves by breeding. But exploiting them caused their populations to collapse or disappear in just a few short decades. It's a startling fact that such "renewable" resources keep running short, while no non-renewable resource has yet run out: not oil, gold, uranium or phosphate. The stone age did not end for lack of stone (a remark often attributed to the former Saudi oil minister Sheikh Ahmed Zaki Yamani).
Guano, a key contributor to 19th-century farming, was renewable fertilizer, made from seabird dung harvested off Peruvian and Namibian islands, but it soon ran out. Modern synthetic fertilizer is made from the air and returns to the air via denitrifying bacteria, yet few would call it a renewable resource. Even fossil fuels are renewable in the sense that they are still being laid down somewhere in the world—not nearly as fast as we use them, of course, but then that's true of Haiti's forests and Newfoundland's cod as well.
And then there is nuclear power. Uranium is not renewable, but plutonium is, in the sense that you can "breed" it in the right kind of reactor. Given how much we dislike plutonium and breeder reactors, it seems that the more renewable nuclear fuel is, the less we like it.
All in all, once you examine it closely, the idea that "renewable" energy is green and clean looks less like a deduction than a superstition.