THE planet-wide industrial exhalation of previously fossilised
carbon is not the only way that humans are changing the Earth's
climate. There are other greenhouse gases, other atmospheric
pollutants, the effects of cutting down forests, and more:
together these things may contribute almost as much as carbon
emissions to global warming. In the face of an international
inability to put the sort of price on carbon use that would
drive its emission down, an increasing number of policy wonks,
and the politicians they advise, are taking a more serious look
at these other factors as possible ways of controlling climate
change.  Three things make these alternative approaches
attractive by comparison. The first is that the emission of
carbon dioxide is a fundamental part of today's industrial
infrastructure. The same is not true for, say, HFC-134a, a gas
with various industrial uses that delivers more than 1,000 times
more warming than carbon dioxide, mass for mass. Something
peripheral for which alternatives can be r