Following the latest report of the United Nations climate change panel, there has been a flurry of renewed interest in so-called geo-engineering projects to counter the warming effects of rising CO2 levels.
Some wild-sounding schemes have been proposed over the years. Here is a sampling:
1. Pumping sulphur into the atmosphere. Injecting millions of tonnes of sulphur into the upper atmosphere would reflect 1% of sunlight back into space to keep the Earth cool, an idea proposed by Nobel-Prize-winning chemist Paul Crutzen. On the downside, it would increase acid rain and might cause respiratory problems, too.
2. Trillions of little sunshades in space (pictured). More like lenses than shades, these would bend sunlight away from Earth, reducing the light hitting the planet by about 2%. Although the shades would be simple and lightweight, it would still cost trillions of dollars to build and launch so many of them, according to astronomer Roger Angel of the University of Arizona, who is championing the idea.
3. A giant orbiting dust cloud. Vast quantities of dust obtained by vaporising a comet – or collecting lunar dust – could be injected into an orbit similar to the Moon's. The dust cloud would eclipse the Sun for several hours each month, cutting the total amount of sunlight reaching Earth per month by more than 1%, according to a proposal by astronomer Curtis Struck of Iowa State University. On the downside, the particles making up the cloud would eventually spiral towards Earth in huge numbers, hitting and possibly destroying satellites.
4. Painting the ground white. We could cover roads, oceans, deserts or other surfaces with reflective material, thereby increasing the amount of sunlight reflected back into space. On the downside, changing the amount of solar energy absorbed by the ground or oceans could have unanticipated effects on the weather.
Some of these ideas are discussed in the February issue of Physics World.
All of these would be vast undertakings requiring huge amounts of money. But I think option 4, especially if confined only to roads and other artificial surfaces, would be the most practical, with the least potential for bad side effects.
Of course, there is also the option of making serious efforts to reduce our reliance on fossil fuels. The world contains finite amounts of oil, so this is a habit we will have to kick eventually anyway. Aside from preventing the most extreme climate change, this would have some other benefits, such as reducing smog and removing a source of conflict in the world.
What do you think – does even entertaining these ideas take focus away from practical, if somewhat inconvenient, steps we will have to take to reduce greenhouse gas emissions, such as driving our cars less? Or is the problem so dire that we should consider every possible measure to reduce the impact of global warming?
David Shiga, online astronomy reporter (Illustration: Roger Angel/UA Steward Observatory)