Blocking the Sun: Study Looks at Costs of 6 Geoengineering Schemes

As the planet warms and the world continues to emit greenhouse gases at a searing pace, some argue that geoengineering ideas are rapidly becoming attractive, if not downright necessary. For the uninitiated, the Royal Society defines geoengineering as (pdf) "The deliberate large-scale intervention in the Earth's climate system, in order to moderate global warming." In other words, hack the planet.

One of the two main categories of geoengineering is solar radiation management, or SRM. (The other is the direct removal of carbon dioxide from the atmosphere.) The idea is to mimic what volcanos do naturally, by putting aerosol particles into the stratosphere on a massive scale. For example, when Mount Pinatubo erupted (image, above) in 1991, the cloud that encircled the planet caused an overall cooling of about half a degree. An argument has been raging for years now about the wisdom of creating our own version of a volcanic eruption: Can it be done? Should it be done? What are the risks? What are the benefits? A few countries and research groups have tried to start demonstration projects; even these proof-of-concept exercises have garnered significant backlash from the scientific community as well as the public at large.

Most scientists would agree, though, that geoengineering ideas are at least worth looking into. And one of the primary questions is whether we can afford to do it. A new study published in the journal Environmental Research Letters has done a thorough cost analysis of the main techniques for SRM—importantly, this is not a cost-benefit analysis, where risks and benefits are included, but simply a look at the costs of putting enough aerosols into the atmosphere. What they found is either encouraging or terrifying, depending on one's feelings about geoengineering: it is, in the grand scheme of things, very, very cheap.

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.

The authors conclude, as others have in the past, that hacking the planet is "feasible from an engineering standpoint." They are quick to point out, though, the technical achievability and relative affordability "[do] not mean that SRM is a preferred strategy." There is still much work to be done on the risks of such large-scale science experiments, and critics often point out that blocking the sun's rays as a way to bring down temperatures does nothing to stop the rapid acidification of the oceans.

Still, the cost analysis and the continued international failure to act on climate change make geoengineering ever more intriguing. The authors point out that the estimated costs of unabated climate change range between $200 billion and $2 trillion per year by 2030 (and some estimates, like the Stern Review, lean even higher, toward 5 percent of global GDP per year). Cutting back on emissions is everyone's first choice for fighting back, but every year of inaction leads us closer to the geoengineering precipice.

Image via D Harlow/USGS

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