Yesterday I talked about the phenomenon of "global dimming", where pollution particles suspended in the atmosphere reflect sunlight back into space. Because they cause less sunlight to hit the Earth, these particles also cool the planet.
So here's an idea for fighting global warming. Instead of trying to reduce greenhouse gas pollution – the root cause of the problem – why not use technology to counteract the effect of the pollution? For example, we could artificially add to the planet's reflectivity so that the warming is cancelled by the cooling.
Using planetary-scale engineering to counteract climate change is called "geo-engineering". A number of geo-engineering ideas have been put forward recently. You can find many of them in this special issue of Climatic Change. One idea would place large, highly-reflective rafts on the ocean. Another would position mirrors in orbit around the Earth.
Yet another idea is based on the phenomenon of global dimming – cool the earth by adding reflective particles to the atmosphere. Deliberately polluting the lower atmosphere, where we live and breathe, isn't such a good idea because of the nasty health consequences. But there is another way: add reflective particles to the upper atmosphere.
The idea is to fly airplanes into the stratosphere, 10 miles or more above the Earth’s surface, and release sulfur dioxide. The sulfur dioxide will be converted into tiny sulfate particles and, presto chango, you're cooling the planet.
Doing this in the stratosphere has two advantages: (1) The particles would be in the upper atmosphere and not in the air we breathe, and (2) While particles in the lower atmosphere remain suspended only for a couple of weeks, particles in the stratosphere stay there for years, so much less sulfur dioxide is needed.
This idea may seem far-fetched, but it has technical merit. One of its staunchest proponents is Paul Crutzen, winner of the Nobel Prize for Chemistry for his work on stratospheric ozone depletion (and also, incidentally, a colleague of mine). But although it has technical merit, and it's great that scientists like Paul are investigating every possibility, I think it's premature to contemplate such drastic measures. The technologies needed to reduce greenhouse gas pollution are already in hand (see my post on Green Technologies), and geo-engineering is a risky proposition.
For one thing, adding particles to the stratosphere may exacerbate stratospheric ozone depletion. Plus we just don’t know what may happen when we start tinkering with the planet. Ed Tenner has a great book on this subject titled Why Things Bite Back. One of the many examples he gives is refrigeration technology. We wanted to use something other than toxic ammonia for cooling so we turned to chlorofluorocarbons, but these turned out to have a dangerous effect on the ozone layer.
The most important reason, however, is this. Even if we could completely cancel the warming effects of greenhouse gas pollution, we would still have another profoundly dangerous consequence to contend with: ocean acidification. And that is the topic of my next post, so be sure to tune in.