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Tarmo ToikkanenSome scientists think climate change needs a more radical approach. As well as trying to curb greenhouse-gas emissions, they have plans to re-engineer the Earth
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When civilian flights over the United States stopped in the wake of the terrorist attacks of September 2001, the lack of sulphur-laden contrails led to a perceptible rise in temperature.
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16 Sep 08
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07 Sep 08
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05 Sep 08
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The Venusian atmosphere is too thick. It creates a large greenhouse effect and cooks a planet that is, in any case, closer to the sun than the Earth is to even higher temperatures than it would otherwise experience.
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One is to remove excess carbon dioxide from the atmosphere. The other is to compensate for the climate-warming greenhouse effect this carbon dioxide and other gases cause, by reducing the amount of sunlight reaching the ground.
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One widely discussed idea
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bloom when iron is added. What is not clear is what happens to the carbon.
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during recent ice ages the cold, dry conditions caused a lot of iron-rich dust to blow around. Supporters of the iron-fertilisation theory believe this dust produced blooms of oceanic algae that then sank to the seabed, taking large amounts of carbon with them, which helped to reduce temperatures still further.
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These are single-celled algae which seem to absorb almost all of the extra carbon dioxide captured when the ocean is fertilised with iron. The crucial question is what happens to these diatoms when they die. If enough of them sink to the ocean floor and stay buried there, the idea should work. If they do not, it won’t.
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The advantage of fertilising the oceans is that it could be done with existing technology. The disadvantage is the unknown knock-on effects. Planktonic algae are at the bottom of the food chain. If more of them are around, the rest of that chain will be affected. This could be a good thing, of course. More algae might mean more krill, and that might mean more whales and other large sea animals.
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shallow-water blooms caused by nitrate and phosphate pollution often swamp the local environment.
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genetically modified trees might grow faster. Such trees are being developed to help the lumber, pulp and biofuel industries. But fast-growing forests could also be planted in order to capture carbon dioxide quickly.
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recycling carbon dioxide from the atmosphere into fuel, by reacting it with hydrogen. Of course, that would require a supply of hydrogen, and producing hydrogen takes energy—which would have to be generated in a way that produces no carbon dioxide.
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eject carbon dioxide from the atmosphere at the Earth’s poles, using the planet’s magnetic field
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oxygen already leaks out this way
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using lasers to ionise molecules of carbon dioxide, and radio waves to get them to spin at the correct rate, would cause those molecules to spiral away from Earth along the lines of magnetic force until they were lost for ever in space.
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Reflecting sunlight back into outer space (increasing the Earth’s albedo
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to increase the amount of pollution in the atmosphere. Governments have spent the past half-century trying to reduce the amount of sulphur compounds in the air. These compounds are the main cause of acid rain. They also, however, have a tendency to form tiny particles that reflect sunlight back into space. That effect is most noticeable when a volcano erupts explosively, as Mount Pinatubo did in 1991, or Tambora did in 1815.
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The year after Tambora’s explosion was known for a long time as the “year without a summer”.
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When civilian flights over the United States stopped in the wake of the terrorist attacks of September 2001, the lack of sulphur-laden contrails led to a perceptible rise in temperature.
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the idea of deliberately polluting the stratosphere with sulphate
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To offset the rise in temperature expected by the middle of the century if things carry on as they are, the amount of sunlight reaching the Earth’s surface would have to be cut by just 1.1%.
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It would require the addition of about 10m tonnes of finely divided sulphate particles to the stratosphere each year.
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If aviation fuel were used in this way, and was 5% sulphur (between ten and 100 times today’s levels), it would require 1m flights a year to the middle of the stratosphere (between 15km and 25km up), assuming an average flight was four hours. Those flights alone would use up half as much fuel as civil aviation now consumes.
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you could achieve part of the effect by making civil aviation use dirty, high-sulphur fuel. It would not be a perfect solution. Civilian jets cruise at an altitude of 10km, the bottom of the stratosphere, and any sulphate they released would thus fall to earth faster.
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to tinker with cloud cover
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looking into how clouds might be made more reflective. Their answer is to spray them with seawater. Particles of salt formed by the evaporation of ocean spray act as nuclei around which the droplets of water that form clouds can condense.
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Increasing the number of particles increases the number of droplets. That does not change the total amount of cloud (which is controlled by the amount of water vapour in the atmosphere). But having more, smaller droplets does increase a cloud’s reflectivity.
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Their answer was that it could, but it would require 1.4 billion tonnes of seawater to be converted into spray each year.
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it would have the advantage of an almost instant off switch. Stop spraying, and things would revert to normal within a couple of days.
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carbon dioxide does not just warm the atmosphere. It also makes the oceans more acidic. That is bad because many marine creatures rely on shells made of calcium carbonate to protect themselves.
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The other fear is of moral hazard—the possibility that people would see the promise of geo-engineering their way out of trouble, despite its risks and uncertainties, as an excuse to continue to pollute the atmosphere as usual.
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the sort of geo-engineering schemes they describe might buy the world 20 to 30 years to adjust. That breathing space would be useful if something really bad, such as the collapse into the sea of part of the Greenland ice-shelf, was in imminent danger of happening
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Some tinkering to suit local needs may be possible.
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it may be feasible to place sulphates in the stratosphere near the poles and thus cool the Earth in a place where global warming manifests itself most strongly, though that would scarcely please the Russians and the Canadians.
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It would be a big experiment, but it would at least be a planned one—unlike the equally big, but unplanned experiment that is now being conducted by motor cars, power stations, cement factories and logging companies all across the planet.
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04 Sep 08
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