Tomorrow is Today

New Study Reviews Economics of Geoengineering Proposals to Fight Global Warming

The Verdict? Safety concerns aside, the cost of Solar Radiation Management (SRM) using existing technologies is not prohibitive.

The authors, Justin McClellan, David Keith, and Jay Apt, found six main schemes for SRM:

1. Existing airplanes: Using aircraft to drop lots of aerosols into the stratosphere is the simplest method. Existing planes would require modification to fly high enough, which does increase the cost; still, putting one million metric tons of aerosols between 20 and 30 km into the air would require a mere $1 to $3 billion per year. 
2. New airplanes: Those modifications required for existing aircraft suggest that simply designing new ones for this purpose might be the way to go. The cost analysis indicates a slightly cheaper overall price, probably below $2 billion per year to provide the same output. 
3. Guns: This is, obviously, a radically different approach. Starting with a two-decade-old analysis of using a battleship-based 16” Mark 7 naval gun to distribute aerosols, the study also looked into newer ideas including electromagnetic and hydrogen gas-based gun systems. Perhaps not surprisingly, delivering the required payload by firing guns into the sky does not turn out to be the cheapest way to go ($137 billion per year, using the original Mark 7 gun; $19 billion per year with a modernized version of the gun). 
4. Rockets: Or more accurately, rocket-powered gliders. This sounds incredibly cool, but again, the costs go well beyond the stratosphere. Even using “off-the-shelf rocket engines” (I, for one, have never seen such a shelf) the cost to distribute enough aerosols would be a stunning $390 billion per year. 
5. Airships: The authors note that airships—i.e., blimps—are attractive because of a large payload capacity and long endurance potential. Getting them up high enough and into strong wind shears will be a problem, though; costs are similar to that for aircraft, in the $2 billion per year range, with much of that going toward high-altitude R&D. 
6. Pipes: The most far-fetched idea has arguably come closest to being implemented. Akin to “space elevator” schemes, this involves a 20-kilometer pipe running from the ground and suspended by helium balloons. Crazy, right? Well, one demonstration experiment planned in the United Kingdom was scrapped only after some patent conflict-of-interest issues were raised. In this analysis, the pipe method would cost a modest $4 to $10 billion per year.

(via Blocking the Sun: Study Looks at Costs of 6 Geoengineering Schemes - IEEE Spectrum)