Engineering a cooler planet is both possible and affordable

10 September 2012
Posted by Alan Boyd.

What do aeroplanes, airships, rockets, guns and gas pipes have in common?  They could all help to cool the Earth by delivering millions of tonnes of global warming-busting aerosols into the Earth's stratosphere.

AeroplaneA group of researchers at Aurora Flight Sciences, Harvard University and Carnegie Mellon University conducted a study to predict the cost of using 6 possible systems to put 1-5 million tonnes of material into the atmosphere, at altitudes of 18-25 km in the Tropics.  The prediction of the costs involved was based on previous statistical models developed for use in the aeronautics industry.   The systems included retrofitting existing aircraft, designing new types of aircraft or airship, or shooting material into the sky using rockets or modified artillery guns.  The group even considered permanently suspending a 20km long pipe from a helium-filled floating platform in the stratosphere.

These systems would deliver a slurry of material into the atmosphere that would increase the reflectivity (or albedo) of the Earth by reflecting the Sun's rays in the same way as a mirror reflects light, resulting in a reduction in energy reaching the surface and heating up the planet.

The study, published in IOP Publishing's journal Environmental Research Letters, found that the design and deployment of new high-altitude aircraft was by far the cheapest possible option, with costs of around $1-2 billion dollars.  The most expensive options were the rocket and gun-based deployment systems, costing 10 or 100 times more than the other options due mainly to their lack of reusability.  This may sound extremely expensive, but the cost of reducing carbon dioxide emissions is currently estimated to reach between 0.2 and 2.5 per cent of U.S. Gross Domestic Product (GDP), which is the total value of the goods and services produced by a country in a year by the year 2030, or roughly $200 to $2000 billion.

The more original ideas, using an airship or suspended pipe system led to a high degree of uncertainty, due to the difficulty in predicting their cost of development from a basic idea to a fully functional system.  However, the predictions show that the suspended pipe would, if successfully implemented, give the cheapest recurring cost-per-kilogram of particles delivered of all the systems considered.

The authors of the paper stress that reducing incident sunlight using aerosols does not reduce concentrations of greenhouse gas in the atmosphere, nor does it combat the resulting rise in the acid content of the oceans, again due to the increase in greenhouse gases.  Rather, as co-author Professor Jay Apt of Carnegie Mellon University, comments, "If for some reason, we are unable to stop ourselves from putting greenhouse gasses in the atmosphere...then it's useful to have in our hip-pocket an understanding of what the emergency measures are that might quickly cool the planet."

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