Engineering a Better Climate
Aerosol particles, seawater mist, and transparent screens in space-can these seemingly madcap geo-engineering ideas be the answer to global warming?Everybody talks about global warming but nobody does anything about it.Well, almost nobody.While world leaders bicker about how to slow the pace of global climate change, some scientists are proposing audacious global engineering schemes that would actually reverse the effects of global warming. The proposals sound like chapters from a half-baked science-fiction thriller, but today's science fiction may become tomorrow's global energy policy-particularly if the earth's climate system abruptly changes for the worse.The National Academy of Sciences and Britain's Royal Society are preparing reports on the possible benefits and dangers of global climate engineering, and the Obama administration has promised to at least consider such plans. One recent study, by researchers Dr. Eric J. Bickel and Lee Lane, contends that we could cancel out this century's global warming by spending about $9 billion on climate engineering, and that such an approach could benefit the planet as much as carbon cuts, at a fraction of the cost.But critics say that tinkering with the earth's climate could have unforeseen and disastrous consequences, and that such would-be climate "fixes" deflect attention from harder truths: the need to make sharp cuts in carbon emissions.Here's a look at some of the leading climate engineering proposals-and some possible of their problems:
Proposal: Release aerosol particles into the atmosphere to reflect solar radiation back into space.How It Would Work: A concentrated stream of sulfur dioxide particles released into the troposphere and lower stratosphere would reproduce the effects of volcanic eruptions such as that of Mount Pinatubo in 1991, which was followed by a global cooling of about 1 degree Fahrenheit. The effects of an aerosol release would gradually dissipate as the particles fell back to Earth, just as the sulphate from volcanoes eventually disperse. Keeping the planet cooled with aerosol releases would cost an estimated $30 billion per year if the particles were fired from military artillery guns, or $8 billion annually if delivered by aircraft, according to a recent report by a climate engineering study group sponsored by the nonprofit Novim Group. The study's authors say the aerosol scheme could be tested on a small scale-say, an experiment to cool a small portion of the Arctic-before being implemented globally.Possible Problems: The planet's climate system might be too complex-and the unintended consequences too dire-for the aerosol plan to be considered safe. Aerosol releases could make matters worse if the particles don't dissipate as quickly as anticipated. Even a closely monitored aerosol release would likely affect different areas of the planet in varying ways, greatly increasing international tensions between climate "winners" and "losers." An aerosol release program costing billions of dollars would be seen by some as a convenient substitute for reductions in greenhouse gas emission, undercutting efforts to deal with the root causes of the climate change problem. A small-scale experimental release of aerosols might not yield clear results, and would need to be observed for a long time in order to produce meaningful data.
Proposal: Spray seawater mist from ships into low-lying clouds to cool the Earth.How it Would Work: This scheme, sometimes called "marine cloud whitening," would shoot an extremely fine mist of sea spray into low clouds so that the clouds become brighter and reflect more sunlight away from Earth. This cloud-brightening technology was deemed the most promising form of climate engineering in the aforementioned study by Bickel and Lane. Preliminary calculations by the researchers show that marine cloud whitening could produce enough cooling to offset a doubling of atmospheric greenhouse gas concentrations, at a cost of no more than $9 billion. Compared to sulphur dioxide aerosol releases, marine cloud whitening is considered less risky, since it introduces natural sea spray into the air, and the particles would precipitate quickly.Possible Problems: Besides the danger of unintended consequences inherent in any planetary-scale climate engineering plan, marine cloud whitening faces potential technical and political problems. No one has come up with a practical way to produce a seawater aerosol of the required volume and concentration, or developed a reliable device to launch the spray into low-lying clouds. A large flotilla of ships numbering in the thousands would have to be deployed across the globe to spray the sea mist, and disputes are likely among countries over the coverage area and who gets to define what the optimum climate should be.
Proposal: Install arrays of pulsed lasers at mountain altitudes that would selectively destroy chlorofluorocarbons in the atmosphere and reduce the greenhouse effect.How it Would Work: A National Academy of Sciences study team looked into the laser idea in the 1990s. A large array of pulsed lasers deployed on mountain peaks would focus intense infrared beams into the troposphere. The lasers would selectively destroy chlorofluorocarbons through a process known as multiphoton dissociation, a technique that fragments gas molecules.Possible Problems: The laser proposal hasn't advanced much beyond the idea stage. No one has come up with a workable plan to build and install a laser array, or determined how many lasers would be needed and at what cost. The National Academy of Sciences study into climate engineering technologies couldn't put a price tag on the laser plan, and warned that climate-changing technologies should not be implemented "without careful assessment of their direct and indirect consequences."
Proposal: Deploy an array of space-based sun shields that would focus small amounts of the sun's light away from Earth.How it Would Work: The idea of using an array of screens in space has been kicking around for more than a decade. The latest proposal comes from the University of Arizona astronomer and optics expert Roger Angel, who suggests launching of a vast network of two-foot wide thin transparent disks into orbit above the earth. Each disk would act as lens, collecting a small amount of the sun's energy and focusing it away from Earth. The units would feature tilting reflecting panels and solar-powered positioning controls to help prevent collisions. Angel's proposed sun shield array-to be deployed if climate change takes a sudden turn for the worse-would cut incoming sunlight by an estimated 1.8 percent, and counteract the warming expected from a doubling of atmospheric carbon dioxide.Possible Problems: Even Angel admits that his plan would require a stupendous number of sun shields-as many as 16 trillion refractors flying in formation over an area of nearly 3 million square miles. Even if such an ambitious plan was successfully deployed, it would be almost impossible to ensure that some screens wouldn't fail and fall back to Earth. Such a technically complex array of reflectors would inevitably be funded and controlled by a few major powers, but everyone would suffer the consequences.
Proposal: Capture and remove carbon dioxide already in the air through a variety of "carbon scrubbing" techniques.How it Would Work: Carbon scrubbing is by far the most predictable form of climate engineering. It doesn't introduce foreign substances into the atmosphere, but rather aims to clean the air that's already there. One proposed carbon scrubbing technique is to build so-called "synthetic trees"-high-tech towers with specially designed resin filters that capture CO2 in the air and collect it for later processing or storage. Klaus Lackner, a geophysicist at Columbia, says that while the technology is expensive (about $30,000 per tower), the first synthetic trees could be up and running within about two years.Possible Problems: Capturing CO2 after it has been released into the atmosphere will never be as effective as capturing it at the source or preventing it from being emitted in the first place. A Royal Society scientist estimated that millions of CO2 scrubbers would have to be deployed to make a significant dent in global warming, at a cost of about $20 trillion. The enormous amount of money needed to scrub the atmosphere of considerable amounts of CO2 would be better spent on reducing or eliminating carbon emissions in the first place.
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