I recently attended a weekend-long conference on climate change. Now, a week later, what sticks out in my memory are two comments. The former was by a U of T climatologist, Richard Peltier. During a question period after the panel where he had spoken, I asked about global dimming, expressing uncertainty as to which is more accurate, the original theory that particulates, clouds, and contrails actually are cooling the planet, but thereby masking the extent of the warming that otherwise would be attributable to greenhouse gases, or on the other hand, the newer notion that water vapor has a cooling effect, whereas soot from industrialization is having a warming effect. This second theory would be a happier one, since it would be easier to remove the soot than the greenhouse gases from the atmosphere.
Peltier replied rather too succinctly; he said that global dimming has been debunked. I wish he had spelled out what the current theory is about which atmospheric pollutants heat and which ones cool the planet. However, at my prompting he did say that this is good news. I’d like to make sure that I understand the situation more fully. As a fellow behind me pointed out, there is the awkward fact that Mt. Pinatubo cooled the planet with its particulates. So how does that square with the theory that particulates heat instead of cool? I haven’t got it clear in my head yet.
The other memorable comment was by Tad Homer-Dixon, who gave the longest address, spelling out the scientific facts about climate change. By now his message is old news to me. What did get my attention was his statement about “geo-engineering,” term that I have never heard before. Its meaning is obvious. It refers to the climate-management proposals that go beyond the reduction of greenhouse gases. These are expensive, often irreversible measures that should only be undertaken as a last desperate attempt to save the planet from catastrophe when it has become apparent that mitigation measures will fall short.
Geo-engineering includes such wild proposals as installing mirrors or foil reflectors in outer space to block the sun’s rays. Or building artificial trees that will absorb the carbon dioxide already ambient in the atmosphere. Or spraying sea water into the atmosphere to dim the incoming rays. Or sprinkling iron filings into the ocean to feed plankton, which will function as carbon sinks.
Homer-Dixon said that a couple of years ago he was horrified by such schemes, but now he has changed his mind. We have come to such a serious point now that all the proposals being entertained at present are inadequate. We must consider these draconian measures. Within two or three years, he says, everyone will be talking about some of these ideas. He is already planning to go to a conference at Harvard about geo-engineering solutions.
Oddly, I have never tipped, since I’d never felt any horror about such proposals from the outset. If anything, I find them encouraging. There are still some tricks up humanity's sleeve. We can pull it off! Immediately I wanted to talk about the practical considerations: expense, for example. And irreversibility. I wouldn’t be keen to put reflectors into outer space because someday we’d have to send up a big vacuum cleaner to suck them back again. Let’s start with something cheap and reversible, such as spraying water into the atmosphere – if indeed that has promise. I need to understand more about global dimming to know whether that is the way it actually works.