The global warming news is grim. Just two recent headlines: Acid oceans need urgent action  and Irreversible climate change due to carbon dioxide emissions . If you follow anybody’s writing on the topic (e.g. mine 2005  and 2007 ) you know all too much about the grimness. But where we make our mistake, you and me, is assuming that once the slower people finally recognize the facts, they’ll want to stop poisoning the planet.
Now that they’re finally noticing that we’re headed to a hot place in a handbasket, they have a better answer. Geoengineering ! We’re so good at controlling planetary processes, the best thing to do is mess with them!
Here, just for kicks, are some of the bright ideas, ranging in light level from black hole to guttering-candle-in-the-darkness. (To be fair to some of the scientists involved, they’re perfectly aware that the best of these are stopgaps, not solutions.)
Air pollution. No, really, there are people proposing this in all seriousness. Sulfur-based aerosols belching out of smokestacks have many nasty consequences, including acid rain for instance, but they also generate smog and cut down on how much sunlight reaches the ground. Carbon dioxide pollution has been mitigated by sulfate pollution. Since global warming is a bad problem, it’s obviously a good idea to kill forests, reduce crop yields, make the ozone problems worse, and increase asthma. Also  “it would change winds and precipitation as well, in ways that are not yet foreseeable. As less sunlight reached the earth’s surface, there would be less evaporation, particularly in the tropics, which would probably make rain and freshwater scarcer than they are today.” If it turns out to be a disaster, there’s no way to remove the sulfates from the air quickly. And the neatest thing about it? Sulfate geoengineering is “cheap enough that single actors could do it and bear the cost themselves.” No international treaties (or restraint) needed. Reducing pollution is for hippie wusses.
Seeding iron into low nutrient areas of the ocean, especially the South Pacific near Antarctica. When plants grow they take carbon out of the air to do it. Phytoplankton are tiny plants, and in some parts of the ocean the only thing holding them back is a lack of iron. Fertilize the ocean with iron and, presto, the phytoplankton grow like mad, die, and settle to the bottom taking their carbon down with them. Sounds good, until you apply a bit of common sense. This is the same process we see in a stagnant pond. Excess nutrients lead to an algal bloom which then dies and sinks to the bottom. The dead plant material is digested by microbes which use oxygen. Since there’s a lot of dead stuff, there are so many microbes they use up all the dissolved oxygen in the water. That means everything else in there dies. This is not good. Just because the ocean is a big place does not make the problem smaller. Furthermore, calculations show  that until you turn lots of ocean into a scum pond, it doesn’t capture enough carbon to make a dent. And it is not reversible.
Space-based solar screen 1. The first version involves lofting millions of small spacecraft that would form a sun shield swarm. Unlike the previous two ideas, this one could, technically speaking, work. A thorough review of the feasibility of various geoengineering methods published by a group at the University of East Anglia  has the numbers. (Link is to a popular summary. Abstract  with link to (for pay) original.) It would take around 135,000 launches per year for years to loft the required number of satellites. That’s about 15 per hour, one every four minutes. It couldn’t be done by conventional rockets because the pollution would cause more problems than they solve. Electromagnetic rail guns firing more or less continuously would be needed, and, obviously, that technology hasn’t been used outside of small-scale lab projects. It uses a lot of power. If the power production generates carbon, it becomes a three steps forward, two back type of thing.
And then, there’s this small problem: “Any interruption in the particle deployment (if, for example, we fell behind on the 135,000 space launches per year required to maintain an effective sunshade) would unleash extremely rapid warming.”
We don’t know much about how plants will react to the change in light. That includes the oceans’ phytoplankton which generate over half the world’s oxygen.
On the plus side, this method could be reversible if each little spacecraft could self-destruct on command.
Price tag: around 3 to 5 trillion dollars.
Space-based solar screen 2. In this version, silicon particles are lofted into the upper stratosphere. As Benford  (yes, the physicist who also write science fiction) says:
[Tiny particles of diatomaceous earth] about 80,000 feet up in the stratosphere [are]. . . . chemically inert, cheap as earth, and readily crushable to the size we want. . . . This could initially be tested over the Arctic, where . . . atmospheric circulation patterns would mostly confine the deployed particles around the North Pole. . . . . The fact that such an experiment is reversible is just as important as the fact that it’s regional. . . . “Applying these technologies in the Arctic zone or even over the whole planet would be so cheap that many private parties could do it on their own. . . . You could do this for a hundred million bucks a year. You could do the whole planet for a couple of billion. That’s amazingly cheap.”
I’m not sure how they plan to get the rocks up there — and these are rocks although individually they’re very small rocks. Rocks are heavy. They must not be planning on using rockets or aircraft, because the pollution would be huge and the cost high. But it sure would take an awful lot of balloons. I’m also not convinced that cheap is good (see Option 1 above). On the plus side, if enough silicon is up there, it is capable of creating noticeable cooling.
Small scale methods that don’t work. Albedo is the term for earth’s reflectivity. There are many ways to increase albedo besides putting silicon in the stratosphere. Unfortunately, the easy ones, like painting roofs and parking lots white, don’t cover enough area so they can’t make a dent in global warming . Another current favorite is biochar. Biomass burned at high temperatures, say in a power plant, creates charcoal which is then buried, taking its carbon out of the atmosphere. A fine idea, but the East Anglia people did the calculations for any practical amount of biomass processing and concluded it couldn’t make a difference. (Biochar may be useful in other contexts, just not to abate global warming.)
(Before anyone suggests nuclear power as a solution, please solve all these problems  first. Just a sampling: uranium is finite resource and practical stocks would run out in less than a century; radioactive pollution in mining, use, and disposal, even with the potential for new accelerated waste processing ; impractically long lead time even with a super-fast construction schedule; and — for all that — an inability to generate more than a small fraction of the power needed.)
Increasing marine albedo This is another idea, together with the one to float tiny rocks, that might be worth trying, but, again, ONLY as an assist to transition to rational energy production. Understanding it requires a bit of background. Salt spray in the oceans rises together with water evaporating. Marine clouds formed this way cover about 25% of the oceans. As the cloud droplets evaporate, the salt crystals remain and reflect more light than plain water.
The idea is to use automated ships to spray seawater using solar and wind power  and therefore increase the amount of salt spray evaporating into the atmosphere. The numbers indicate it could noticeably affect warming. And it’s reversible assuming that the ships are biodegradable. Like all the methods, it has its unknowns and downsides.
[The sprayers are] mounted on an unmanned, satellite-guided sailing ship. More specifically, the vessel would be a Flettner ship, which has tall, spinning cylinders that resemble smokestacks but act as sails, generating lift because one side is moving with the wind and the other side against it.
In Salter’s concept, turbines spun by water moving past the ship would generate the electricity to keep the cylinders spinning and also to spray seawater out the stacks in 0.8-micron droplets. Salter and Latham estimate that 1,500 ships, each spraying eight gallons a second—and each costing $2 million, for a total of $3 billion—could offset the global warming caused by a doubling of CO2. Half the job could be done, according to modeling results from the Met Office Hadley Center for Climate Prediction and Research in Exeter, England, by deploying ships over just 4 percent of the ocean.
Still, no one has modeled how evenly the cooling would spread around the planet. “You could end up with a polka-dotted world, where there are really cold places and really hot places,” Battisti says. Another concern is drought downwind of the spray vessels; clouds made of many small droplets last longer, which is desirable in a sunshade, but they also produce less rain.
The biggest problem with fixes isn’t even that people will use them as an excuse to keep making the problem worse. (“What, me, worry? We’ll just toss some iron at the South Pole!”) The biggest problem is applying a fix, getting used to it, and then having it fail. We’d get sudden, extreme warming, which is the only thing worse than our current gradual warming.
The sad thing is really that it’s all perseverance worthy of a better cause. As one of the scientists himself says,
It would “require such a Herculean effort, that maybe it’s easier to build wind turbines and solar power plants [and implement efficiency ].”
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