'Geoengineering' is a new term, still seeking a definition. It seems t
o imply something global, intentional, and unnatural. For the radiatio
n balance, geoengineering may be fifty years in the future; today's me
ans may be out of date then, and the future means are not yet known. I
t might immensely simplify greenhouse policy, transforming it from an
exceedingly complicated regulatory regime to a problem in internationa
l cost sharing, a problem that we are familiar with. Putting things in
the stratosphere or in orbit can probably be done by 'exo-national' p
rograms, not depending on the behavior of populations, not requiring n
ational regulations or incentives, not dependent on universal particip
ation. It will involve merely deciding what to do, how much to do, and
who is to pay for it.