Irrespective of whether you believe in anthropogenic climate change, the facts are simple and incontrovertible: The world is getting warmer, and if it continues to get much warmer we will soon be in a lot of trouble. Low-lying nations will flood, many species will go extinct as their climates are destroyed, it will become even harder to grow crops in Africa, and it will yet again be possible to make wine in England.

There are two possible escape routes that would allow us to maintain the status quo. The easiest solution is to very, very rapidly reduce greenhouse gas emissions — but really, at this point, it looks like this isn’t going to happen. The second path, which has been shunned for decades by scientists and plebs alike, but which is now looking more and more like the only viable option, is geoengineering.

Geoengineering is the act of deliberately altering the world’s climate, with the purpose of controlling global warming. Basically, instead of kindly asking humans to alter their behavior and reduce greenhouse emissions, geoengineering is the nuclear, carpet-bombing approach to global warming.

There are two main schools of geoengineering: solar radiation management (SRM), and carbon dioxide removal.

Carbon dioxide removal generally revolves around the use of simple organisms, such as phytoplankton, to capture carbon dioxide from the air — and then burying that organism underground or undersea. It is very easy to encourage a phytoplankton bloom by adding iron to the ocean (pictured right). We’d need to do this on a very large scale, but it could significantly reduce the greenhouse effect.

Solar radiation management is as awesome as it sounds: It’s basically a bunch of techniques that blot out the sky, preventing sunlight from entering our atmosphere, and thus lowering the Earth’s temperature. One (theoretical) SRM approach actually involves blocking out the sun with a space-based sunshade, just like Mr. Burns in The Simpsons. The most cost effective SRM techniques, however, are stratospheric albedo modification, or in plain English: Increasing the reflectiveness of clouds.

In much the same way that a large volcano eruption kicks up enough dust into the atmosphere to block sunlight, these approaches involve the pumping of millions of tons of dust (aerosol) into the atmosphere every year, effectively creating a new Earth atmosphere that blocks more of the Sun’s radiation. In a recent paper titled “Cost analysis of stratospheric albedo modification delivery systems,” three American researchers discuss six different ways of launching dust into the atmosphere — and some of the approaches are rather interesting.

The first three are humdrum: Modified 747s (they have to reach 18km/11mi high); new planes specifically designed to dump dust in the stratosphere; and rockets. The other three are much more exciting: guns (as in, huge, battleship guns); airships; and a “floating platform with slurry pipe” (i.e. a low-level space elevator that constantly pumps dust into the atmosphere).

According to the researchers, using specialized airplanes is the cheapest method, costing about $10 billion to get off the ground and then $2 billion a year to fly a few metric tons of dust into the atmosphere. The floating slurry pipe is cheaper in the long term, but significantly more expensive to get up and running. Rockets, unsurprisingly, are completely unfeasible ($2.3 trillion initial outlay, and $400 billion per year). Guns would be cheap to convert, but operational costs would be a very dear $137 billion per year.

Rather worryingly, the paper doesn’t discuss the fact that Earth’s last extinction event — the event that wiped out the dinosaurs — was caused by a massive asteroid or comet colliding with Earth and kicking up so much dust that the Sun was almost completely blocked out, causing temperatures to plummeted low enough to kill off many complex lifeforms. But I’m sure we’ll get a grasp on our greenhouse gas emissions before we’re forced to pump that much dust into the atmosphere…

Research paper: doi:10.1088/1748-9326/7/3/034019 (free to read, for now)