Blogging has been light, and will remain so through Sunday; I’m at a conference on energy and terrorism sponsored by the Foundation for Research on Economics and the Environment.
In today’s discussion about energy policy and global warming, Tom Schelling made a logical point that was new to me — though apparently it has been made in some of the technical literature — and seemed tremendously important.
The global temperature depends on how much radiation gets to the Earth from the Sun, and how much the Earth radiates back into space. If in fact (1) human activities are reducing the rate at which energy leaves the planet — which seems very likely — and (2) the resulting temperature increase and associated changes in climate and weather patterns will be disastrous — which seems plausible but is not certain — it is not the case that our only options for dealing with that problem involve reducing our contribution to the greenhouse effect. The alternative would be to take more actions that decrease incoming energy.
It turns out that the aerosols and particulates we emit tend to increase the reflectance (albedo) of the planet; if in fact there was more warming early in the 20th century than later in the century, the reason may be that late in the century we put more sulfur oxides into the atmosphere. That was a bad idea in terms of acid rain, but perhaps it moderated the warming effect.
So, Schelling asked, how much would it cost to increase the Earth’s albedo by enough to offset the damage from increased greenhouse-gas emissions? The necessary change involves a fraction of a percent of incident solar energy, not enough to be observable without precise instruments. Some apparently minor changes might do the trick: slightly degrading the performance of jet aircraft engines could put more carbon black into the statosphere. A higher-tech solution would be to put lots of reflective mylar in low-earth orbit; a lower-tech solution would be to scatter lots of ping-pong balls in tropical waters; an extremely cute solution, if practicable, would be to stimulate the formation of cirrus clouds over parts of the Pacific Ocean.
Of course any and all of these might turn out to have unwanted side effects. But any attempt to massively reduce greenhouse gas production would be certain to have big unwanted side effects. And, as Schelling pointed out, if we can find cheap means of increasing the albedo we avoid some horrendous diplomatic problems along with huge economic sacrifices.
It seems to me that, in political terms, those who want to resist calls for controls on GHG emissions would be better off pushing low-cost albedo-increasing measures than trying to deny that anthropogenic global warming is real or trying to pretend that letting the global temperature rise another couple of degrees Celsius represents a prudent risk.