On the different kinds of geoengineering

Q. Could you offer a rough taxonomy of types of geoengineering? Which of them should we be taking seriously?

A. One of the first things I found out was, this is field of wacky ideas. I talked to a guy who thought it would be great to spread Special K out in the ocean to reflect sunlight and cool the earth’s temperature. People who want to launch nuclear bombs at the moon, to shoot moon dust into the outer space to reflect sunlight away. I try to focus on the serious ones. There are two distinct kinds.

One is what the British Royal Society, which did a big report on this last year, termed “solar radiation management” or “solar shielding.” It’s about blocking sunlight. In order to offset the temperature change from a doubling of CO2 emissions, you only have to reflect a small amount of sunlight away from the earth — one or two percent.

Of the solar radiation management technologies that can do this, there are two that people are thinking about seriously. One is spraying particles into the stratosphere — sulphate particles, similar to what comes out of coal plants except without all the dirty metallic toxins, or in the future, particles specifically engineered out of inert metals. So acid rain, pollution, inhaling them … you’re not going to have snow drops of this stuff raining down on your house or anything like that. It could potentially change the color of the sky somewhat. It could have aesthetic effects. But we don’t know of any health effects yet.

Another way is brightening clouds, which turns out to be the organic, homegrown version of solar radiation management. You can throw seawater into certain marine clouds that would act as cloud condensation nuclei and make the droplets smaller. Smaller droplets have more surface area, so they make the cloud a brighter color and it reflects away more sunlight. It’s a little difficult to imagine cloud writing used for the whole earth, but you could use it in specific areas, the Arctic or Greenland.

The other category is carbon dioxide removal — machines and technologies that can pull CO2 out of the atmosphere. These are far less problematic, politically and morally. One of the scientists I write about in the book is David Keith at the University of Calgary, who is starting a company to build enormous machines that can suck CO2 out of the atmosphere the way CO2 is sucked out of the stack of a power plant. There are some advantages to this because you can locate these machines anywhere. They are very expensive now, but there’s a lot of potential.

There are other ways of sucking up CO2. The most well known to many people is dumping iron slurry into the ocean to stimulate plankton blooms. The plankton absorb carbon and then, in theory, sink down to the bottom of the ocean and sequester it. Many problems with that — we don’t know how much is actually sucked up and how much makes it to the bottom. Another technique is biochar, a way of burning charcoal and burying it in the soil to increase the uptake of carbon in the soil.

There are lots of other ideas, but these are the main things that I talk about in the book.

Q. I noticed you left out white roofs and other small-scale efforts.

A. White roofs are a great example of things we are already doing to change the reflectivity, or albedo, of the earth. They have other benefits, like lowering the temperature of the house and reducing air-conditioning costs, but even if you whitened every roof on the planet, it still wouldn’t have much effect.